NFC documentation overhaul.

Change-Id: I45dca95a24b2d0327e080436fbcc7b1dad79de02

10 files changed, 711 insertions, 301 deletions

diff --git a/core/java/android/nfc/tech/IsoDep.java b/core/java/android/nfc/tech/IsoDep.java
index 774982e..2a132f9 100644
--- a/core/java/android/nfc/tech/IsoDep.java
+++ b/core/java/android/nfc/tech/IsoDep.java
@@ -24,18 +24,14 @@ import android.util.Log;
 import java.io.IOException;
 
 /**
- * A low-level connection to a {@link Tag} using the ISO-DEP technology, also known as
- * ISO1443-4.
+ * Provides access to ISO-DEP (ISO 14443-4) properties and I/O operations on a {@link Tag}.
  *
- * <p>You can acquire this kind of connection with {@link #get}.
- * Use this class to send and receive data with {@link #transceive transceive()}.
- *
- * <p>Applications must implement their own protocol stack on top of
- * {@link #transceive transceive()}.
- *
- * <p class="note"><strong>Note:</strong>
- * Use of this class requires the {@link android.Manifest.permission#NFC}
- * permission.
+ * <p>Acquire a {@link IsoDep} object using {@link #get}.
+ * <p>The primary ISO-DEP I/O operation is {@link #transceive}. Applications must
+ * implement their own protocol stack on top of {@link #transceive}.
+ * <p>Tags that enumerate the {@link IsoDep} technology in {@link Tag#getTechList}
+ * will also enumerate
+ * {@link NfcA} or {@link NfcB} (since IsoDep builds on top of either of these).
  */
 public final class IsoDep extends BasicTagTechnology {
     private static final String TAG = "NFC";
@@ -49,10 +45,13 @@ public final class IsoDep extends BasicTagTechnology {
     private byte[] mHistBytes = null;
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link IsoDep} for the given tag.
+     * <p>Does not cause any RF activity and does not block.
+     * <p>Returns null if {@link IsoDep} was not enumerated in {@link Tag#getTechList}.
+     * This indicates the tag does not support ISO-DEP.
      *
-     * @param tag The tag to get the tech from
+     * @param tag an ISO-DEP compatible tag
+     * @return ISO-DEP object
      */
     public static IsoDep get(Tag tag) {
         if (!tag.hasTech(TagTechnology.ISO_DEP)) return null;
@@ -62,7 +61,7 @@ public final class IsoDep extends BasicTagTechnology {
             return null;
         }
     }
-    
+
     /** @hide */
     public IsoDep(Tag tag)
             throws RemoteException {
@@ -75,13 +74,13 @@ public final class IsoDep extends BasicTagTechnology {
     }
 
     /**
-     * Sets the timeout of an IsoDep transceive transaction in milliseconds.
-     * If the transaction has not completed before the timeout,
-     * any ongoing {@link #transceive} operation will be
-     * aborted and the connection to the tag is lost. This setting is applied
-     * only to the {@link Tag} object linked to this technology and will be
-     * reset when {@link IsoDep#close} is called.
-     * The default transaction timeout is 300 milliseconds.
+     * Set the timeout of {@link #transceive} in milliseconds.
+     * <p>The timeout only applies to ISO-DEP {@link #transceive}, and is
+     * reset to a default value when {@link #close} is called.
+     * <p>Setting a longer timeout may be useful when performing
+     * transactions that require a long processing time on the tag
+     * such as key generation.
+     * @param timeout timeout value in milliseconds
      */
     public void setTimeout(int timeout) {
         try {
@@ -102,29 +101,51 @@ public final class IsoDep extends BasicTagTechnology {
     }
 
     /**
-     * Return the historical bytes if the tag is using {@link NfcA}, null otherwise.
+     * Return the ISO-DEP historical bytes for {@link NfcA} tags.
+     * <p>Does not cause any RF activity and does not block.
+     * <p>The historical bytes can be used to help identify a tag. They are present
+     * only on {@link IsoDep} tags that are based on {@link NfcA} RF technology.
+     * If this tag is not {@link NfcA} then null is returned.
+     * <p>In ISO 14443-4 terminology, the historical bytes are a subset of the RATS
+     * response.
+     *
+     * @return ISO-DEP historical bytes, or null if this is not a {@link NfcA} tag
      */
     public byte[] getHistoricalBytes() {
         return mHistBytes;
     }
 
     /**
-     * Return the hi layer response bytes if the tag is using {@link NfcB}, null otherwise.
+     * Return the higher layer response bytes for {@link NfcB} tags.
+     * <p>Does not cause any RF activity and does not block.
+     * <p>The higher layer response bytes can be used to help identify a tag.
+     * They are present only on {@link IsoDep} tags that are based on {@link NfcB}
+     * RF technology. If this tag is not {@link NfcB} then null is returned.
+     * <p>In ISO 14443-4 terminology, the higher layer bytes are a subset of the
+     * ATTRIB response.
+     *
+     * @return ISO-DEP historical bytes, or null if this is not a {@link NfcB} tag
      */
     public byte[] getHiLayerResponse() {
         return mHiLayerResponse;
     }
 
     /**
-     * Send data to a tag and receive the response.
-     * <p>
-     * This method will block until the response is received. It can be canceled
-     * with {@link #close}.
-     * <p>Requires {@link android.Manifest.permission#NFC} permission.
+     * Send raw ISO-DEP data to the tag and receive the response.
+     *
+     * <p>Applications must only send the INF payload, and not the start of frame and
+     * end of frame indicators. Applications do not need to fragment the payload, it
+     * will be automatically fragmented and defragmented by {@link #transceive} if
+     * it exceeds FSD/FSC limits.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
      *
-     * @param data bytes to send
-     * @return bytes received in response
-     * @throws IOException if the target is lost or connection closed
+     * @param data command bytes to send, must not be null
+     * @return response bytes received, will not be null
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or this operation is canceled
      */
     public byte[] transceive(byte[] data) throws IOException {
         return transceive(data, true);
diff --git a/core/java/android/nfc/tech/MifareClassic.java b/core/java/android/nfc/tech/MifareClassic.java
index d337ead..268fe95 100644
--- a/core/java/android/nfc/tech/MifareClassic.java
+++ b/core/java/android/nfc/tech/MifareClassic.java
@@ -25,32 +25,61 @@ import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 
 /**
- * Technology class representing MIFARE Classic tags (also known as MIFARE Standard).
+ * Provides access to MIFARE Classic properties and I/O operations on a {@link Tag}.
  *
- * <p>Support for this technology type is optional. If the NFC stack doesn't support this technology
- * MIFARE Classic tags will still be scanned, but will only show the NfcA technology.
+ * <p>Acquire a {@link MifareClassic} object using {@link #get}.
  *
- * <p>MIFARE Classic tags have sectors that each contain blocks. The block size is constant at
- * 16 bytes, but the number of sectors and the sector size varies by product. MIFARE has encryption
- * built in and each sector has two keys associated with it, as well as ACLs to determine what
- * level acess each key grants. Before operating on a sector you must call either
- * {@link #authenticateSectorWithKeyA(int, byte[])} or
- * {@link #authenticateSectorWithKeyB(int, byte[])} to gain authorization for your request.
+ * <p>MIFARE Classic is also known as MIFARE Standard.
+ * <p>MIFARE Classic tags are divided into sectors, and each sector is sub-divided into
+ * blocks. Block size is always 16 bytes ({@link #BLOCK_SIZE}. Sector size varies.
+ * <ul>
+ * <li>MIFARE Classic Mini are 320 bytes ({@link #SIZE_MINI}), with 5 sectors each of 4 blocks.
+ * <li>MIFARE Classic 1k are 1024 bytes ({@link #SIZE_1K}), with 16 sectors each of 4 blocks.
+ * <li>MIFARE Classic 2k are 2048 bytes ({@link #SIZE_2K}), with 32 sectors each of 4 blocks.
+ * <li>MIFARE Classic 4k} are 4096 bytes ({@link #SIZE_4K}). The first 32 sectors contain 4 blocks
+ * and the last 8 sectors contain 16 blocks.
+ * </ul>
+ *
+ * <p>MIFARE Classic tags require authentication on a per-sector basis before any
+ * other I/O operations on that sector can be performed. There are two keys per sector,
+ * and ACL bits determine what I/O operations are allowed on that sector after
+ * authenticating with a key. {@see #authenticateSectorWithKeyA} and
+ * {@see #authenticateSectorWithKeyB}.
+ *
+ * <p>Three well-known authentication keys are defined in this class:
+ * {@link #KEY_DEFAULT}, {@link #KEY_MIFARE_APPLICATION_DIRECTORY},
+ * {@link #KEY_NFC_FORUM}.
+ * <ul>
+ * <li>{@link #KEY_DEFAULT} is the default factory key for MIFARE Classic.
+ * <li>{@link #KEY_MIFARE_APPLICATION_DIRECTORY} is the well-known key for
+ * MIFARE Classic cards that have been formatted according to the
+ * MIFARE Application Directory (MAD) specification.
+ * <li>{@link #KEY_NFC_FORUM} is the well-known key for MIFARE Classic cards that
+ * have been formatted according to the NFC
+ *
+ * <p>Implementation of this class on a Android NFC device is optional.
+ * If it is not implemented, then
+ * {@link MifareClassic} will never be enumerated in {@link Tag#getTechList}.
+ * If it is enumerated, then all {@link MifareClassic} I/O operations will be supported,
+ * and {@link Ndef#MIFARE_CLASSIC} NDEF tags will also be supported. In either case,
+ * {@link NfcA} will also be enumerated on the tag, because all MIFARE Classic tags are also
+ * {@link NfcA}.
  */
 public final class MifareClassic extends BasicTagTechnology {
     /**
-     * The well-known default MIFARE read key. All keys are set to this at the factory.
-     * Using this key will effectively make the payload in the sector public.
+     * The default factory key.
      */
     public static final byte[] KEY_DEFAULT =
             {(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF,(byte)0xFF};
     /**
-     * The well-known, default MIFARE Application Directory read key.
+     * The well-known key for tags formatted according to the
+     * MIFARE Application Directory (MAD) specification.
      */
     public static final byte[] KEY_MIFARE_APPLICATION_DIRECTORY =
             {(byte)0xA0,(byte)0xA1,(byte)0xA2,(byte)0xA3,(byte)0xA4,(byte)0xA5};
     /**
-     * The well-known, default read key for NDEF data on a MIFARE Classic
+     * The well-known key for tags formatted according to the
+     * NDEF on Mifare Classic specification.
      */
     public static final byte[] KEY_NFC_FORUM =
             {(byte)0xD3,(byte)0xF7,(byte)0xD3,(byte)0xF7,(byte)0xD3,(byte)0xF7};
@@ -64,19 +93,19 @@ public final class MifareClassic extends BasicTagTechnology {
     /** A MIFARE Pro tag */
     public static final int TYPE_PRO = 2;
 
-    /** The tag contains 16 sectors, each holding 4 blocks. */
+    /** Tag contains 16 sectors, each with 4 blocks. */
     public static final int SIZE_1K = 1024;
-    /** The tag contains 32 sectors, each holding 4 blocks. */
+    /** Tag contains 32 sectors, each with 4 blocks. */
     public static final int SIZE_2K = 2048;
     /**
-     * The tag contains 40 sectors. The first 32 sectors contain 4 blocks and the last 8 sectors
+     * Tag contains 40 sectors. The first 32 sectors contain 4 blocks and the last 8 sectors
      * contain 16 blocks.
      */
     public static final int SIZE_4K = 4096;
-    /** The tag contains 5 sectors, each holding 4 blocks. */
+    /** Tag contains 5 sectors, each with 4 blocks. */
     public static final int SIZE_MINI = 320;
 
-    /** Size of a Mifare Classic block (in bytes) */
+    /** Size of a MIFARE Classic block (in bytes) */
     public static final int BLOCK_SIZE = 16;
 
     private static final int MAX_BLOCK_COUNT = 256;
@@ -87,10 +116,14 @@ public final class MifareClassic extends BasicTagTechnology {
     private int mSize;
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link MifareClassic} for the given tag.
+     * <p>Does not cause any RF activity and does not block.
+     * <p>Returns null if {@link MifareClassic} was not enumerated in {@link Tag#getTechList}.
+     * This indicates the tag is not MIFARE Classic compatible, or this Android
+     * device does not support MIFARE Classic.
      *
-     * @param tag The tag to get the tech from
+     * @param tag an MIFARE Classic compatible tag
+     * @return MIFARE Classic object
      */
     public static MifareClassic get(Tag tag) {
         if (!tag.hasTech(TagTechnology.MIFARE_CLASSIC)) return null;
@@ -160,17 +193,31 @@ public final class MifareClassic extends BasicTagTechnology {
         }
     }
 
-    /** Returns the type of the tag, determined at discovery time */
+    /**
+     * Return the type of this MIFARE Classic compatible tag.
+     * <p>One of {@link #TYPE_UNKNOWN}, {@link #TYPE_CLASSIC}, {@link #TYPE_PLUS} or
+     * {@link #TYPE_PRO}.
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return type
+     */
     public int getType() {
         return mType;
     }
 
-    /** Returns the size of the tag in bytes, determined at discovery time */
+    /**
+     * Return the size of the tag in bytes
+     * <p>One of {@link #SIZE_MINI}, {@link #SIZE_1K}, {@link #SIZE_2K}, {@link #SIZE_4K}.
+     * These constants are equal to their respective size in bytes.
+     * <p>Does not cause any RF activity and does not block.
+     * @return size in bytes
+     */
     public int getSize() {
         return mSize;
     }
 
-    /** Returns true if the tag is emulated, determined at discovery time.
+    /**
+     * Return true if the tag is emulated, determined at discovery time.
      * These are actually smart-cards that emulate a Mifare Classic interface.
      * They can be treated identically to a Mifare Classic tag.
      * @hide
@@ -179,7 +226,11 @@ public final class MifareClassic extends BasicTagTechnology {
         return mIsEmulated;
     }
 
-    /** Returns the number of sectors on this tag, determined at discovery time */
+    /**
+     * Return the number of MIFARE Classic sectors.
+     * <p>Does not cause any RF activity and does not block.
+     * @return number of sectors
+     */
     public int getSectorCount() {
         switch (mSize) {
         case SIZE_1K:
@@ -195,12 +246,21 @@ public final class MifareClassic extends BasicTagTechnology {
         }
     }
 
-    /** Returns the total block count, determined at discovery time */
+    /**
+     * Return the total number of MIFARE Classic blocks.
+     * <p>Does not cause any RF activity and does not block.
+     * @return total number of blocks
     public int getBlockCount() {
         return mSize / BLOCK_SIZE;
     }
 
-    /** Returns the block count for the given sector, determined at discovery time */
+    /**
+     * Return the number of blocks in the given sector.
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @param sectorIndex index of sector, starting from 0
+     * @return number of blocks in the sector
+     */
     public int getBlockCountInSector(int sectorIndex) {
         validateSector(sectorIndex);
 
@@ -211,7 +271,13 @@ public final class MifareClassic extends BasicTagTechnology {
         }
     }
 
-    /** Return the sector index of a given block */
+    /**
+     * Return the sector that contains a given block.
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @param blockIndex index of block to lookup, starting from 0
+     * @return sector index that contains the block
+     */
     public int blockToSector(int blockIndex) {
         validateBlock(blockIndex);
 
@@ -222,7 +288,13 @@ public final class MifareClassic extends BasicTagTechnology {
         }
     }
 
-    /** Return the first block of a given sector */
+    /**
+     * Return the first block of a given sector.
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @param sectorIndex index of sector to lookup, starting from 0
+     * @return block index of first block in sector
+     */
     public int sectorToBlock(int sectorIndex) {
         if (sectorIndex < 32) {
             return sectorIndex * 4;
@@ -231,22 +303,51 @@ public final class MifareClassic extends BasicTagTechnology {
         }
     }
 
-    // Methods that require connect()
     /**
-     * Authenticate a sector.
-     * <p>Every sector has an A and B key with different access privileges,
-     * this method attempts to authenticate against the A key.
-     * <p>This requires a that the tag be connected.
+     * Authenticate a sector with key A.
+     *
+     * <p>Successful authentication of a sector with key A enables other
+     * I/O operations on that sector. The set of operations granted by key A
+     * key depends on the ACL bits set in that sector. For more information
+     * see the MIFARE Classic specification on {@see http://www.nxp.com}.
+     *
+     * <p>A failed authentication attempt causes an implicit reconnection to the
+     * tag, so authentication to other sectors will be lost.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param sectorIndex index of sector to authenticate, starting from 0
+     * @param key 6-byte authentication key
+     * @return true on success, false on authentication failure
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public boolean authenticateSectorWithKeyA(int sectorIndex, byte[] key) throws IOException {
         return authenticate(sectorIndex, key, true);
     }
 
     /**
-     * Authenticate a sector.
-     * <p>Every sector has an A and B key with different access privileges,
-     * this method attempts to authenticate against the B key.
-     * <p>This requires a that the tag be connected.
+     * Authenticate a sector with key B.
+     *
+     * <p>Successful authentication of a sector with key B enables other
+     * I/O operations on that sector. The set of operations granted by key B
+     * depends on the ACL bits set in that sector. For more information
+     * see the MIFARE Classic specification on {@see http://www.nxp.com}.
+     *
+     * <p>A failed authentication attempt causes an implicit reconnection to the
+     * tag, so authentication to other sectors will be lost.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param sectorIndex index of sector to authenticate, starting from 0
+     * @param key 6-byte authentication key
+     * @return true on success, false on authentication failure
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public boolean authenticateSectorWithKeyB(int sectorIndex, byte[] key) throws IOException {
         return authenticate(sectorIndex, key, false);
@@ -291,8 +392,15 @@ public final class MifareClassic extends BasicTagTechnology {
 
     /**
      * Read 16-byte block.
-     * <p>This requires a that the tag be connected.
-     * @throws IOException
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param blockIndex index of block to read, starting from 0
+     * @return 16 byte block
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public byte[] readBlock(int blockIndex) throws IOException {
         validateBlock(blockIndex);
@@ -304,8 +412,15 @@ public final class MifareClassic extends BasicTagTechnology {
 
     /**
      * Write 16-byte block.
-     * <p>This requires a that the tag be connected.
-     * @throws IOException
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param blockIndex index of block to write, starting from 0
+     * @param data 16 bytes of data to write
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public void writeBlock(int blockIndex, byte[] data) throws IOException {
         validateBlock(blockIndex);
@@ -323,9 +438,16 @@ public final class MifareClassic extends BasicTagTechnology {
     }
 
     /**
-     * Increment a value block, and store the result in temporary memory.
-     * @param blockIndex
-     * @throws IOException
+     * Increment a value block, storing the result in the temporary block on the tag.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param blockIndex index of block to increment, starting from 0
+     * @param value non-negative to increment by
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public void increment(int blockIndex, int value) throws IOException {
         validateBlock(blockIndex);
@@ -342,9 +464,16 @@ public final class MifareClassic extends BasicTagTechnology {
     }
 
     /**
-     * Decrement a value block, and store the result in temporary memory.
-     * @param blockIndex
-     * @throws IOException
+     * Decrement a value block, storing the result in the temporary block on the tag.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param blockIndex index of block to decrement, starting from 0
+     * @param value non-negative to decrement by
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public void decrement(int blockIndex, int value) throws IOException {
         validateBlock(blockIndex);
@@ -361,9 +490,15 @@ public final class MifareClassic extends BasicTagTechnology {
     }
 
     /**
-     * Copy from temporary memory to value block.
-     * @param blockIndex
-     * @throws IOException
+     * Copy from the temporary block to a value block.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param blockIndex index of block to copy to
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public void transfer(int blockIndex) throws IOException {
         validateBlock(blockIndex);
@@ -375,9 +510,15 @@ public final class MifareClassic extends BasicTagTechnology {
     }
 
     /**
-     * Copy from value block to temporary memory.
-     * @param blockIndex
-     * @throws IOException
+     * Copy from a value block to the temporary block.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param blockIndex index of block to copy from
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public void restore(int blockIndex) throws IOException {
         validateBlock(blockIndex);
@@ -390,15 +531,16 @@ public final class MifareClassic extends BasicTagTechnology {
 
     /**
      * Send raw NfcA data to a tag and receive the response.
-     * <p>
-     * This method will block until the response is received. It can be canceled
-     * with {@link #close}.
-     * <p>Requires {@link android.Manifest.permission#NFC} permission.
-     * <p>This requires a that the tag be connected.
      *
-     * @param data bytes to send
-     * @return bytes received in response
-     * @throws IOException if the target is lost or connection closed
+     * <p>This is equivalent to connecting to this tag via {@link NfcA}
+     * and calling {@link NfcA#transceive}. Note that all MIFARE Classic
+     * tags are based on {@link NfcA} technology.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @see NfcA#transceive
      */
     public byte[] transceive(byte[] data) throws IOException {
         return transceive(data, true);
diff --git a/core/java/android/nfc/tech/MifareUltralight.java b/core/java/android/nfc/tech/MifareUltralight.java
index b514f1c..5971708 100644
--- a/core/java/android/nfc/tech/MifareUltralight.java
+++ b/core/java/android/nfc/tech/MifareUltralight.java
@@ -17,6 +17,7 @@
 package android.nfc.tech;
 
 import android.nfc.Tag;
+import android.nfc.TagLostException;
 import android.os.RemoteException;
 
 import java.io.IOException;
@@ -24,14 +25,13 @@ import java.io.IOException;
 //TOOD: Ultralight C 3-DES authentication, one-way counter
 
 /**
- * Technology class representing MIFARE Ultralight and MIFARE Ultralight C tags.
+ * Provides access to MIFARE Ultralight properties and I/O operations on a {@link Tag}.
  *
- * <p>Support for this technology type is optional. If the NFC stack doesn't support this technology
- * MIFARE Ultralight class tags will still be scanned, but will only show the NfcA technology.
+ * <p>Acquire a {@link MifareUltralight} object using {@link #get}.
  *
- * <p>MIFARE Ultralight compatible tags have 4 byte pages. The read command
- * returns 4 pages (16 bytes) at a time, for speed. The write command operates
- * on a single page (4 bytes) to minimize EEPROM write cycles.
+ * <p>MIFARE Ultralight compatible tags have 4 byte pages {@link #PAGE_SIZE}.
+ * The primary operations on an Ultralight tag are {@link #readPages} and
+ * {@link #writePage}.
  *
  * <p>The original MIFARE Ultralight consists of a 64 byte EEPROM. The first
  * 4 pages are for the OTP area, manufacturer data, and locking bits. They are
@@ -44,6 +44,13 @@ import java.io.IOException;
  * and authentication configuration and are readable. The final 4 pages are for
  * the authentication key and are not readable. For more information see the
  * NXP data sheet MF0ICU2.
+ *
+ * <p>Implementation of this class on a Android NFC device is optional.
+ * If it is not implemented, then
+ * {@link MifareUltralight} will never be enumerated in {@link Tag#getTechList}.
+ * If it is enumerated, then all {@link MifareUltralight} I/O operations will be supported.
+ * In either case, {@link NfcA} will also be enumerated on the tag,
+ * because all MIFARE Ultralight tags are also {@link NfcA} tags.
  */
 public final class MifareUltralight extends BasicTagTechnology {
     /** A MIFARE Ultralight compatible tag of unknown type */
@@ -62,10 +69,15 @@ public final class MifareUltralight extends BasicTagTechnology {
     private int mType;
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link MifareUltralight} for the given tag.
+     * <p>Returns null if {@link MifareUltralight} was not enumerated in
+     * {@link Tag#getTechList} - this indicates the tag is not MIFARE
+     * Ultralight compatible, or that this Android
+     * device does not implement MIFARE Ultralight.
+     * <p>Does not cause any RF activity and does not block.
      *
-     * @param tag The tag to get the tech from
+     * @param tag an MIFARE Ultralight compatible tag
+     * @return MIFARE Ultralight object
      */
     public static MifareUltralight get(Tag tag) {
         if (!tag.hasTech(TagTechnology.MIFARE_ULTRALIGHT)) return null;
@@ -93,53 +105,72 @@ public final class MifareUltralight extends BasicTagTechnology {
         }
     }
 
-    /** Returns the type of the tag.
-     * <p>It is very hard to always accurately classify a MIFARE Ultralight
-     * compatible tag as Ultralight original or Ultralight C. So consider
-     * {@link #getType} a hint. */
+    /**
+     * Return the MIFARE Ultralight type of the tag.
+     * <p>One of {@link #TYPE_ULTRALIGHT} or {@link #TYPE_ULTRALIGHT_C} or
+     * {@link #TYPE_UNKNOWN}.
+     * <p>Depending on how the tag has been formatted, it can be impossible
+     * to accurately classify between original MIFARE Ultralight and
+     * Ultralight C. So treat this method as a hint.
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return the type
+     */
     public int getType() {
         return mType;
     }
 
-    // Methods that require connect()
     /**
      * Read 4 pages (16 bytes).
-     * <p>The MIFARE Ultralight protocol always reads 4 pages at a time.
-     * <p>If the read spans past the last readable block, then the tag will
+     *
+     * <p>The MIFARE Ultralight protocol always reads 4 pages at a time, to
+     * reduce the number of commands required to read an entire tag.
+     * <p>If a read spans past the last readable block, then the tag will
      * return pages that have been wrapped back to the first blocks. MIFARE
      * Ultralight tags have readable blocks 0x00 through 0x0F. So a read to
      * block offset 0x0E would return blocks 0x0E, 0x0F, 0x00, 0x01. MIFARE
      * Ultralight C tags have readable blocks 0x00 through 0x2B. So a read to
      * block 0x2A would return blocks 0x2A, 0x2B, 0x00, 0x01.
-     * <p>This requires that the tag be connected.
      *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param pageIndex index of first page to read, starting from 0
      * @return 4 pages (16 bytes)
-     * @throws IOException
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
-    public byte[] readPages(int pageOffset) throws IOException {
-        validatePageOffset(pageOffset);
+    public byte[] readPages(int pageIndex) throws IOException {
+        validatePageIndex(pageIndex);
         checkConnected();
 
-        byte[] cmd = { 0x30, (byte) pageOffset};
+        byte[] cmd = { 0x30, (byte) pageIndex};
         return transceive(cmd, false);
     }
 
     /**
      * Write 1 page (4 bytes).
-     * <p>The MIFARE Ultralight protocol always writes 1 page at a time.
-     * <p>This requires that the tag be connected.
      *
-     * @param pageOffset The offset of the page to write
-     * @param data The data to write
-     * @throws IOException
+     * <p>The MIFARE Ultralight protocol always writes 1 page at a time, to
+     * minimize EEPROM write cycles.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param pageIndex index of page to write, starting from 0
+     * @param data 4 bytes to write
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
-    public void writePage(int pageOffset, byte[] data) throws IOException {
-        validatePageOffset(pageOffset);
+    public void writePage(int pageIndex, byte[] data) throws IOException {
+        validatePageIndex(pageIndex);
         checkConnected();
 
         byte[] cmd = new byte[data.length + 2];
         cmd[0] = (byte) 0xA2;
-        cmd[1] = (byte) pageOffset;
+        cmd[1] = (byte) pageIndex;
         System.arraycopy(data, 0, cmd, 2, data.length);
 
         transceive(cmd, false);
@@ -147,28 +178,29 @@ public final class MifareUltralight extends BasicTagTechnology {
 
     /**
      * Send raw NfcA data to a tag and receive the response.
-     * <p>
-     * This method will block until the response is received. It can be canceled
-     * with {@link #close}.
-     * <p>Requires {@link android.Manifest.permission#NFC} permission.
-     * <p>This requires a that the tag be connected.
      *
-     * @param data bytes to send
-     * @return bytes received in response
-     * @throws IOException if the target is lost or connection closed
+     * <p>This is equivalent to connecting to this tag via {@link NfcA}
+     * and calling {@link NfcA#transceive}. Note that all MIFARE Classic
+     * tags are based on {@link NfcA} technology.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @see NfcA#transceive
      */
     public byte[] transceive(byte[] data) throws IOException {
         return transceive(data, true);
     }
 
-    private static void validatePageOffset(int pageOffset) {
+    private static void validatePageIndex(int pageIndex) {
         // Do not be too strict on upper bounds checking, since some cards
         // may have more addressable memory than they report.
         // Note that issuing a command to an out-of-bounds block is safe - the
         // tag will wrap the read to an addressable area. This validation is a
         // helper to guard against obvious programming mistakes.
-        if (pageOffset < 0 || pageOffset >= MAX_PAGE_COUNT) {
-            throw new IndexOutOfBoundsException("page out of bounds: " + pageOffset);
+        if (pageIndex < 0 || pageIndex >= MAX_PAGE_COUNT) {
+            throw new IndexOutOfBoundsException("page out of bounds: " + pageIndex);
         }
     }
 }
diff --git a/core/java/android/nfc/tech/Ndef.java b/core/java/android/nfc/tech/Ndef.java
index 39ff282..0467473 100644
--- a/core/java/android/nfc/tech/Ndef.java
+++ b/core/java/android/nfc/tech/Ndef.java
@@ -22,6 +22,7 @@ import android.nfc.INfcTag;
 import android.nfc.NdefMessage;
 import android.nfc.NfcAdapter;
 import android.nfc.Tag;
+import android.nfc.TagLostException;
 import android.os.Bundle;
 import android.os.RemoteException;
 import android.util.Log;
@@ -29,11 +30,41 @@ import android.util.Log;
 import java.io.IOException;
 
 /**
- * A high-level connection to a {@link Tag} using one of the NFC type 1, 2, 3, or 4 technologies
- * to interact with NDEF data. MiFare Classic cards that present NDEF data may also be used
- * via this class. To determine the exact technology being used call {@link #getType()}
+ * Provides access to NDEF content and operations on a {@link Tag}.
  *
- * <p>You can acquire this kind of connection with {@link #get}.
+ * <p>Acquire a {@link Ndef} object using {@link #get}.
+ *
+ * <p>NDEF is an NFC Forum data format. The data formats are implemented in
+ * {@link android.nfc.NdefMessage} and
+ * {@link android.nfc.NdefRecord}. This class provides methods to
+ * retrieve and modify the {@link android.nfc.NdefMessage}
+ * on a tag.
+ *
+ * <p>There are currently four NFC Forum standardized tag types that can be
+ * formatted to contain NDEF data.
+ * <ul>
+ * <li>NFC Forum Type 1 Tag ({@link #NFC_FORUM_TYPE_1}), such as the Innovision Topaz
+ * <li>NFC Forum Type 2 Tag ({@link #NFC_FORUM_TYPE_2}), such as the NXP Mifare Ultralight
+ * <li>NFC Forum Type 3 Tag ({@link #NFC_FORUM_TYPE_3}), such as Sony Felica
+ * <li>NFC Forum Type 4 Tag ({@link #NFC_FORUM_TYPE_4}), such as NXP MIFARE Desfire
+ * </ul>
+ * It is mandatory for all Android devices with NFC to correctly enumerate
+ * {@link Ndef} on NFC Forum Tag Types 1-4, and implement all NDEF operations
+ * as defined in this class.
+ *
+ * <p>Some vendors have there own well defined specifications for storing NDEF data
+ * on tags that do not fall into the above categories. Android devices with NFC
+ * should enumerate and implement {@link Ndef} under these vendor specifications
+ * where possible, but it is not mandatory. {@link #getType} returns a String
+ * describing this specification, for example {@link #MIFARE_CLASSIC} is
+ * <code>com.nxp.ndef.mifareclassic</code>.
+ *
+ * <p>Android devices that support MIFARE Classic must also correctly
+ * implement {@link Ndef} on MIFARE Classic tags formatted to NDEF.
+ *
+ * <p>For guaranteed compatibility across all Android devices with NFC, it is
+ * recommended to use NFC Forum Types 1-4 in new deployments of NFC tags
+ * with NDEF payload. Vendor NDEF formats will not work on all Android devices.
  *
  * <p class="note"><strong>Note:</strong>
  * Use of this class requires the {@link android.Manifest.permission#NFC}
@@ -77,14 +108,15 @@ public final class Ndef extends BasicTagTechnology {
     /** @hide */
     public static final String UNKNOWN = "android.ndef.unknown";
 
+    /** NFC Forum Tag Type 1 */
     public static final String NFC_FORUM_TYPE_1 = "org.nfcforum.ndef.type1";
-
+    /** NFC Forum Tag Type 2 */
     public static final String NFC_FORUM_TYPE_2 = "org.nfcforum.ndef.type2";
-
+    /** NFC Forum Tag Type 4 */
     public static final String NFC_FORUM_TYPE_3 = "org.nfcforum.ndef.type3";
-
+    /** NFC Forum Tag Type 4 */
     public static final String NFC_FORUM_TYPE_4 = "org.nfcforum.ndef.type4";
-
+    /** NDEF on MIFARE Classic */
     public static final String MIFARE_CLASSIC = "com.nxp.ndef.mifareclassic";
 
     private final int mMaxNdefSize;
@@ -93,11 +125,19 @@ public final class Ndef extends BasicTagTechnology {
     private final int mNdefType;
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link Ndef} for the given tag.
+     *
+     * <p>Returns null if {@link Ndef} was not enumerated in {@link Tag#getTechList}.
+     * This indicates the tag is not NDEF formatted, or that this tag
+     * is NDEF formatted but under a vendor specification that this Android
+     * device does not implement.
      *
-     * @param tag The tag to get the tech from
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @param tag an MIFARE Classic compatible tag
+     * @return MIFARE Classic object
      */
+
     public static Ndef get(Tag tag) {
         if (!tag.hasTech(TagTechnology.NDEF)) return null;
         try {
@@ -126,22 +166,29 @@ public final class Ndef extends BasicTagTechnology {
     }
 
     /**
-     * Get the primary NDEF message on this tag. This data is read at discovery time
-     * and does not require a connection.
+     * Get the {@link NdefMessage} that was read from the tag at discovery time.
+     *
+     * <p>If the NDEF Message is modified by an I/O operation then it
+     * will not be updated here, this function only returns what was discovered
+     * when the tag entered the field.
+     * <p>Does not cause any RF activity and does not block.
+     * @return NDEF Message read from the tag at discovery time
      */
     public NdefMessage getCachedNdefMessage() {
         return mNdefMsg;
     }
 
     /**
-     * Get NDEF tag type.
+     * Get the NDEF tag type.
+     *
      * <p>Returns one of {@link #NFC_FORUM_TYPE_1}, {@link #NFC_FORUM_TYPE_2},
      * {@link #NFC_FORUM_TYPE_3}, {@link #NFC_FORUM_TYPE_4},
-     * {@link #MIFARE_CLASSIC} or another NDEF tag type that is not yet in the
-     * Android API.
-     * <p>Android devices with NFC support must always correctly enumerate
-     * NFC Forum tag types, and may optionally enumerate
-     * {@link #MIFARE_CLASSIC} since it requires proprietary technology.
+     * {@link #MIFARE_CLASSIC} or another NDEF tag type that has not yet been
+     * formalized in this Android API.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return a string representing the NDEF tag type
      */
     public String getType() {
         switch (mNdefType) {
@@ -161,25 +208,44 @@ public final class Ndef extends BasicTagTechnology {
     }
 
     /**
-     * Get maximum NDEF message size in bytes
+     * Get the maximum NDEF message size in bytes.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return size in bytes
      */
     public int getMaxSize() {
         return mMaxNdefSize;
     }
 
     /**
-     * Provides a hint on whether writes are likely to succeed.
+     * Determine if the tag is writable.
+     *
+     * <p>NFC Forum tags can be in read-only or read-write states.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
      * <p>Requires {@link android.Manifest.permission#NFC} permission.
-     * @return true if write is likely to succeed
+     *
+     * @return true if the tag is writable
      */
     public boolean isWritable() {
         return (mCardState == NDEF_MODE_READ_WRITE);
     }
 
-    // Methods that require connect()
     /**
-     * Get the primary NDEF message on this tag. This data is read actively
-     * and requires a connection.
+     * Read the current {@link android.nfc.NdefMessage} on this tag.
+     *
+     * <p>This always reads the current NDEF Message stored on the tag.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @return the NDEF Message, never null
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
+     * @throws FormatException if the NDEF Message on the tag is malformed
      */
     public NdefMessage getNdefMessage() throws IOException, FormatException {
         checkConnected();
@@ -212,8 +278,16 @@ public final class Ndef extends BasicTagTechnology {
     }
 
     /**
-     * Overwrite the primary NDEF message
-     * @throws IOException
+     * Overwrite the {@link NdefMessage} on this tag.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param msg the NDEF Message to write, must not be null
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
+     * @throws FormatException if the NDEF Message to write is malformed
      */
     public void writeNdefMessage(NdefMessage msg) throws IOException, FormatException {
         checkConnected();
@@ -244,8 +318,11 @@ public final class Ndef extends BasicTagTechnology {
     }
 
     /**
-     * Indicates whether a tag can be made read-only with
-     * {@link #makeReadOnly()}
+     * Indicates whether a tag can be made read-only with {@link #makeReadOnly()}.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return true if it is possible to make this tag read-only
      */
     public boolean canMakeReadOnly() {
         if (mNdefType == TYPE_1 || mNdefType == TYPE_2) {
@@ -256,11 +333,20 @@ public final class Ndef extends BasicTagTechnology {
     }
 
     /**
-     * Sets the CC field to indicate this tag is read-only
-     * and permanently sets the lock bits to prevent any further NDEF
-     * modifications.
-     * This is a one-way process and can not be reverted!
-     * @throws IOException
+     * Make a tag read-only.
+     *
+     * <p>This sets the CC field to indicate the tag is read-only,
+     * and where possible permanently sets the lock bits to prevent
+     * any further modification of the memory.
+     * <p>This is a one-way process and cannot be reverted!
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @return true on success, false if it is not possible to make this tag read-only
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
      */
     public boolean makeReadOnly() throws IOException {
         checkConnected();
diff --git a/core/java/android/nfc/tech/NdefFormatable.java b/core/java/android/nfc/tech/NdefFormatable.java
index e2828b5..84bda87 100644
--- a/core/java/android/nfc/tech/NdefFormatable.java
+++ b/core/java/android/nfc/tech/NdefFormatable.java
@@ -22,15 +22,24 @@ import android.nfc.INfcTag;
 import android.nfc.NdefMessage;
 import android.nfc.NfcAdapter;
 import android.nfc.Tag;
+import android.nfc.TagLostException;
 import android.os.RemoteException;
 import android.util.Log;
 
 import java.io.IOException;
 
 /**
- * An interface to a {@link Tag} allowing to format the tag as NDEF.
+ * Provide access to NDEF format operations on a {@link Tag}.
  *
- * <p>You can acquire this kind of connection with {@link #get}.
+ * <p>Acquire a {@link NdefFormatable} object using {@link #get}.
+ *
+ * <p>Android devices with NFC must only enumerate and implement this
+ * class for tags for which it can format to NDEF.
+ *
+ * <p>Unfortunately the procedures to convert unformated tags to NDEF formatted
+ * tags are not specified by NFC Forum, and are not generally well-known. So
+ * there is no mandatory set of tags for which all Android devices with NFC
+ * must support {@link NdefFormatable}.
  *
  * <p class="note"><strong>Note:</strong>
  * Use of this class requires the {@link android.Manifest.permission#NFC}
@@ -40,10 +49,13 @@ public final class NdefFormatable extends BasicTagTechnology {
     private static final String TAG = "NFC";
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link NdefFormatable} for the given tag.
+     * <p>Does not cause any RF activity and does not block.
+     * <p>Returns null if {@link NdefFormatable} was not enumerated in {@link Tag#getTechList}.
+     * This indicates the tag is not NDEF formatable by this Android device.
      *
-     * @param tag The tag to get the tech from
+     * @param tag an NDEF formatable tag
+     * @return NDEF formatable object
      */
     public static NdefFormatable get(Tag tag) {
         if (!tag.hasTech(TagTechnology.NDEF_FORMATABLE)) return null;
@@ -63,23 +75,43 @@ public final class NdefFormatable extends BasicTagTechnology {
     }
 
     /**
-     * Formats a tag as NDEF, if possible. You may supply a first
-     * NdefMessage to be written on the tag.
-     * <p>Either all steps succeed, or an IOException is thrown if any one step
-     * fails.
+     * Format a tag as NDEF, and write a {@link NdefMessage}.
+     *
+     * <p>This is a multi-step process, an IOException is thrown
+     * if any one step fails.
+     * <p>The card is left in a read-write state after this operation.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param msg the NDEF message to write after formatting
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
+     * @throws FormatException if the NDEF Message to write is malformed
      */
-    public void format(NdefMessage firstMessage) throws IOException, FormatException {
-        format(firstMessage, false);
+    public void format(NdefMessage msg) throws IOException, FormatException {
+        format(msg, false);
     }
 
     /**
-     * Formats a tag as NDEF, if possible. You may supply a first
-     * NdefMessage to be written on the tag.
-     * <p>Either all steps succeed, or an IOException is thrown if any one step
-     * fails.
+     * Formats a tag as NDEF, write a {@link NdefMessage}, and make read-only.
+     *
+     * <p>This is a multi-step process, an IOException is thrown
+     * if any one step fails.
+     * <p>The card is left in a read-only state if this method returns successfully.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
+     *
+     * @param msg the NDEF message to write after formatting
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or the operation is canceled
+     * @throws FormatException if the NDEF Message to write is malformed
      */
-    public void formatReadOnly(NdefMessage firstMessage) throws IOException, FormatException {
-        format(firstMessage, true);
+    public void formatReadOnly(NdefMessage msg) throws IOException, FormatException {
+        format(msg, true);
     }
 
     /*package*/ void format(NdefMessage firstMessage, boolean makeReadOnly) throws IOException,
diff --git a/core/java/android/nfc/tech/NfcA.java b/core/java/android/nfc/tech/NfcA.java
index 24badc4..93d8510 100644
--- a/core/java/android/nfc/tech/NfcA.java
+++ b/core/java/android/nfc/tech/NfcA.java
@@ -23,18 +23,11 @@ import android.os.RemoteException;
 import java.io.IOException;
 
 /**
- * A low-level connection to a {@link Tag} using the NFC-A technology, also known as
- * ISO1443-3A.
+ * Provides access to NFC-A (ISO 14443-3A) properties and I/O operations on a {@link Tag}.
  *
- * <p>You can acquire this kind of connection with {@link #get}.
- * Use this class to send and receive data with {@link #transceive transceive()}.
- *
- * <p>Applications must implement their own protocol stack on top of
- * {@link #transceive transceive()}.
- *
- * <p class="note"><strong>Note:</strong>
- * Use of this class requires the {@link android.Manifest.permission#NFC}
- * permission.
+ * <p>Acquire a {@link NfcA} object using {@link #get}.
+ * <p>The primary NFC-A I/O operation is {@link #transceive}. Applications must
+ * implement their own protocol stack on top of {@link #transceive}.
  */
 public final class NfcA extends BasicTagTechnology {
     /** @hide */
@@ -46,10 +39,13 @@ public final class NfcA extends BasicTagTechnology {
     private byte[] mAtqa;
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link NfcA} for the given tag.
+     * <p>Returns null if {@link NfcA} was not enumerated in {@link Tag#getTechList}.
+     * This indicates the tag does not support NFC-A.
+     * <p>Does not cause any RF activity and does not block.
      *
-     * @param tag The tag to get the tech from
+     * @param tag an NFC-A compatible tag
+     * @return NFC-A object
      */
     public static NfcA get(Tag tag) {
         if (!tag.hasTech(TagTechnology.NFC_A)) return null;
@@ -69,29 +65,44 @@ public final class NfcA extends BasicTagTechnology {
     }
 
     /**
-     * Returns the ATQA/SENS_RES bytes discovered at tag discovery.
+     * Return the ATQA/SENS_RES bytes from tag discovery.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return ATQA/SENS_RES bytes
      */
     public byte[] getAtqa() {
         return mAtqa;
     }
 
     /**
-     * Returns the SAK/SEL_RES discovered at tag discovery.
+     * Return the SAK/SEL_RES bytes from tag discovery.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return SAK bytes
      */
     public short getSak() {
         return mSak;
     }
 
     /**
-     * Send data to a tag and receive the response.
-     * <p>
-     * This method will block until the response is received. It can be canceled
-     * with {@link #close}.
-     * <p>Requires {@link android.Manifest.permission#NFC} permission.
+     * Send raw NFC-A commands to the tag and receive the response.
+     *
+     * <p>Applications must not append the EoD (CRC) to the payload,
+     * it will be automatically calculated.
+     * <p>Applications must only send commands that are complete bytes,
+     * for example a SENS_REQ is not possible (these are used to
+     * manage tag polling and initialization).
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
      *
      * @param data bytes to send
      * @return bytes received in response
-     * @throws IOException if the target is lost or connection closed
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or this operation is canceled
      */
     public byte[] transceive(byte[] data) throws IOException {
         return transceive(data, true);
diff --git a/core/java/android/nfc/tech/NfcB.java b/core/java/android/nfc/tech/NfcB.java
index abeef32..29246ee 100644
--- a/core/java/android/nfc/tech/NfcB.java
+++ b/core/java/android/nfc/tech/NfcB.java
@@ -23,18 +23,11 @@ import android.os.RemoteException;
 import java.io.IOException;
 
 /**
- * A low-level connection to a {@link Tag} using the NFC-B technology, also known as
- * ISO1443-3B.
+ * Provides access to NFC-B (ISO 14443-3B) properties and I/O operations on a {@link Tag}.
  *
- * <p>You can acquire this kind of connection with {@link #get}.
- * Use this class to send and receive data with {@link #transceive transceive()}.
- *
- * <p>Applications must implement their own protocol stack on top of
- * {@link #transceive transceive()}.
- *
- * <p class="note"><strong>Note:</strong>
- * Use of this class requires the {@link android.Manifest.permission#NFC}
- * permission.
+ * <p>Acquire a {@link NfcB} object using {@link #get}.
+ * <p>The primary NFC-B I/O operation is {@link #transceive}. Applications must
+ * implement their own protocol stack on top of {@link #transceive}.
  */
 public final class NfcB extends BasicTagTechnology {
     /** @hide */
@@ -46,10 +39,13 @@ public final class NfcB extends BasicTagTechnology {
     private byte[] mProtInfo;
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link NfcB} for the given tag.
+     * <p>Returns null if {@link NfcB} was not enumerated in {@link Tag#getTechList}.
+     * This indicates the tag does not support NFC-B.
+     * <p>Does not cause any RF activity and does not block.
      *
-     * @param tag The tag to get the tech from
+     * @param tag an NFC-B compatible tag
+     * @return NFC-B object
      */
     public static NfcB get(Tag tag) {
         if (!tag.hasTech(TagTechnology.NFC_B)) return null;
@@ -69,31 +65,43 @@ public final class NfcB extends BasicTagTechnology {
     }
 
     /**
-     * Returns the Application Data bytes from the ATQB/SENSB_RES
-     * bytes discovered at tag discovery.
+     * Return the Application Data bytes from ATQB/SENSB_RES at tag discovery.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return Application Data bytes from ATQB/SENSB_RES bytes
      */
     public byte[] getApplicationData() {
         return mAppData;
     }
 
     /**
-     * Returns the Protocol Info bytes from the ATQB/SENSB_RES
-     * bytes discovered at tag discovery.
+     * Return the Protocol Info bytes from ATQB/SENSB_RES at tag discovery.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return Protocol Info bytes from ATQB/SENSB_RES bytes
      */
     public byte[] getProtocolInfo() {
         return mProtInfo;
     }
 
     /**
-     * Send data to a tag and receive the response.
-     * <p>
-     * This method will block until the response is received. It can be canceled
-     * with {@link #close}.
-     * <p>Requires {@link android.Manifest.permission#NFC} permission.
+     * Send raw NFC-B commands to the tag and receive the response.
+     *
+     * <p>Applications must not append the EoD (CRC) to the payload,
+     * it will be automatically calculated.
+     * <p>Applications must not send commands that manage the polling
+     * loop and initialization (SENSB_REQ, SLOT_MARKER etc).
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
      *
      * @param data bytes to send
      * @return bytes received in response
-     * @throws IOException if the target is lost or connection closed
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or this operation is canceled
      */
     public byte[] transceive(byte[] data) throws IOException {
         return transceive(data, true);
diff --git a/core/java/android/nfc/tech/NfcF.java b/core/java/android/nfc/tech/NfcF.java
index f617739..27d1b57 100644
--- a/core/java/android/nfc/tech/NfcF.java
+++ b/core/java/android/nfc/tech/NfcF.java
@@ -23,18 +23,11 @@ import android.os.RemoteException;
 import java.io.IOException;
 
 /**
- * A low-level connection to a {@link Tag} using the NFC-F technology, also known as
- * JIS6319-4.
+ * Provides access to NFC-F (JIS 6319-4) properties and I/O operations on a {@link Tag}.
  *
- * <p>You can acquire this kind of connection with {@link #get}.
- * Use this class to send and receive data with {@link #transceive transceive()}.
- *
- * <p>Applications must implement their own protocol stack on top of
- * {@link #transceive transceive()}.
- *
- * <p class="note"><strong>Note:</strong>
- * Use of this class requires the {@link android.Manifest.permission#NFC}
- * permission.
+ * <p>Acquire a {@link NfcF} object using {@link #get}.
+ * <p>The primary NFC-F I/O operation is {@link #transceive}. Applications must
+ * implement their own protocol stack on top of {@link #transceive}.
  */
 public final class NfcF extends BasicTagTechnology {
     /** @hide */
@@ -46,10 +39,13 @@ public final class NfcF extends BasicTagTechnology {
     private byte[] mManufacturer = null;
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link NfcF} for the given tag.
+     * <p>Returns null if {@link NfcF} was not enumerated in {@link Tag#getTechList}.
+     * This indicates the tag does not support NFC-F.
+     * <p>Does not cause any RF activity and does not block.
      *
-     * @param tag The tag to get the tech from
+     * @param tag an NFC-F compatible tag
+     * @return NFC-F object
      */
     public static NfcF get(Tag tag) {
         if (!tag.hasTech(TagTechnology.NFC_F)) return null;
@@ -70,24 +66,42 @@ public final class NfcF extends BasicTagTechnology {
         }
     }
 
+    /**
+     * Return the System Code bytes from tag discovery.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return System Code bytes
+     */
     public byte[] getSystemCode() {
       return mSystemCode;
     }
 
+    /**
+     * Return the Manufacturer bytes from tag discovery.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return Manufacturer bytes
+     */
     public byte[] getManufacturer() {
       return mManufacturer;
     }
 
     /**
-     * Send data to a tag and receive the response.
-     * <p>
-     * This method will block until the response is received. It can be canceled
-     * with {@link #close}.
-     * <p>Requires {@link android.Manifest.permission#NFC} permission.
+     * Send raw NFC-F commands to the tag and receive the response.
+     *
+     * <p>Applications must not append the SoD (length) or EoD (CRC) to the payload,
+     * it will be automatically calculated.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
      *
      * @param data bytes to send
      * @return bytes received in response
-     * @throws IOException if the target is lost or connection closed
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or this operation is canceled
      */
     public byte[] transceive(byte[] data) throws IOException {
         return transceive(data, true);
diff --git a/core/java/android/nfc/tech/NfcV.java b/core/java/android/nfc/tech/NfcV.java
index 8e1f066..99dc318 100644
--- a/core/java/android/nfc/tech/NfcV.java
+++ b/core/java/android/nfc/tech/NfcV.java
@@ -23,18 +23,11 @@ import android.os.RemoteException;
 import java.io.IOException;
 
 /**
- * A low-level connection to a {@link Tag} using NFC vicinity technology, also known as
- * ISO15693.
+ * Provides access to NFC-V (ISO 15693) properties and I/O operations on a {@link Tag}.
  *
- * <p>You can acquire this kind of connection with {@link #get}.
- * Use this class to send and receive data with {@link #transceive transceive()}.
- *
- * <p>Applications must implement their own protocol stack on top of
- * {@link #transceive transceive()}.
- *
- * <p class="note"><strong>Note:</strong>
- * Use of this class requires the {@link android.Manifest.permission#NFC}
- * permission.
+ * <p>Acquire a {@link NfcV} object using {@link #get}.
+ * <p>The primary NFC-V I/O operation is {@link #transceive}. Applications must
+ * implement their own protocol stack on top of {@link #transceive}.
  */
 public final class NfcV extends BasicTagTechnology {
     /** @hide */
@@ -47,10 +40,13 @@ public final class NfcV extends BasicTagTechnology {
     private byte mDsfId;
 
     /**
-     * Returns an instance of this tech for the given tag. If the tag doesn't support
-     * this tech type null is returned.
+     * Get an instance of {@link NfcV} for the given tag.
+     * <p>Returns null if {@link NfcV} was not enumerated in {@link Tag#getTechList}.
+     * This indicates the tag does not support NFC-V.
+     * <p>Does not cause any RF activity and does not block.
      *
-     * @param tag The tag to get the tech from
+     * @param tag an NFC-V compatible tag
+     * @return NFC-V object
      */
     public static NfcV get(Tag tag) {
         if (!tag.hasTech(TagTechnology.NFC_V)) return null;
@@ -69,24 +65,43 @@ public final class NfcV extends BasicTagTechnology {
         mDsfId = extras.getByte(EXTRA_DSFID);
     }
 
+    /**
+     * Return the Response Flag bytes from tag discovery.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return Response Flag bytes
+     */
     public byte getResponseFlags() {
         return mRespFlags;
     }
 
+    /**
+     * Return the DSF ID bytes from tag discovery.
+     *
+     * <p>Does not cause any RF activity and does not block.
+     *
+     * @return DSF ID bytes
+     */
     public byte getDsfId() {
         return mDsfId;
     }
 
     /**
-     * Send data to a tag and receive the response.
-     * <p>
-     * This method will block until the response is received. It can be canceled
-     * with {@link #close}.
-     * <p>Requires {@link android.Manifest.permission#NFC} permission.
+     * Send raw NFC-V commands to the tag and receive the response.
+     *
+     * <p>Applications must not append the CRC to the payload,
+     * it will be automatically calculated. The application does
+     * provide FLAGS, CMD and PARAMETER bytes.
+     *
+     * <p>This is an I/O operation and will block until complete. It must
+     * not be called from the main application thread. A blocked call will be canceled with
+     * {@link IOException} if {@link #close} is called from another thread.
      *
      * @param data bytes to send
      * @return bytes received in response
-     * @throws IOException if the target is lost or connection closed
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or this operation is canceled
      */
     public byte[] transceive(byte[] data) throws IOException {
         return transceive(data, true);
diff --git a/core/java/android/nfc/tech/TagTechnology.java b/core/java/android/nfc/tech/TagTechnology.java
index 50df865..be6ccd0 100644
--- a/core/java/android/nfc/tech/TagTechnology.java
+++ b/core/java/android/nfc/tech/TagTechnology.java
@@ -21,6 +21,61 @@ import android.nfc.Tag;
 import java.io.Closeable;
 import java.io.IOException;
 
+/**
+ * {@link TagTechnology} is an interface to a technology in a {@link Tag}.
+ * <p>
+ * Obtain a {@link TagTechnology} implementation by calling the static method <code>get()</code>
+ * on the implementation class.
+ * <p>
+ * NFC tags are based on a number of independently developed technologies and offer a
+ * wide range of capabilities. The
+ * {@link TagTechnology} implementations provide access to these different
+ * technologies and capabilities. Some sub-classes map to technology
+ * specification (for example {@link NfcA}, {@link IsoDep}, others map to
+ * pseudo-technologies or capabilities (for example {@link Ndef}, {@link NdefFormatable}).
+ * <p>
+ * It is mandatory for all Android NFC devices to provide the following
+ * {@link TagTechnology} implementations.
+ * <ul>
+ * <li>{@link NfcA} (also known as ISO 14443-3A)
+ * <li>{@link NfcB} (also known as ISO 14443-3B)
+ * <li>{@link NfcF} (also known as JIS 6319-4)
+ * <li>{@link NfcV} (also known as ISO 15693)
+ * <li>{@link IsoDep}
+ * <li>{@link Ndef} on NFC Forum Type 1, Type 2, Type 3 or Type 4 compliant tags
+ * </ul>
+ * It is optional for Android NFC devices to provide the following
+ * {@link TagTechnology} implementations. If it is not provided, the
+ * Android device will never enumerate that class via {@link Tag#getTechList}.
+ * <ul>
+ * <li>{@link MifareClassic}
+ * <li>{@link MifareUltralight}
+ * <li>{@link NdefFormatable} must only be enumerated on tags for which this Android device
+ * is capable of formatting. Proprietary knowledge is often required to format a tag
+ * to make it NDEF compatible.
+ * </ul>
+ * <p>
+ * {@link TagTechnology} implementations provide methods that fall into two classes:
+ * <em>cached getters</em> and <em>I/O operations</em>.
+ * <h4>Cached getters</h4>
+ * These methods (usually prefixed by <code>get</code> or <code>is</code>) return
+ * properties of the tag, as determined at discovery time. These methods will never
+ * block or cause RF activity, and do not require {@link #connect} to have been called.
+ * They also never update, for example if a property is changed by an I/O operation with a tag
+ * then the cached getter will still return the result from tag discovery time.
+ * <h4>I/O operations</h4>
+ * I/O operations may require RF activity, and may block. They have the following semantics.
+ * <ul>
+ * <li>{@link #connect} must be called before using any other I/O operation.
+ * <li>{@link #close} must be called after completing I/O operations with a
+ * {@link TagTechnology}, and it will cancel all other blocked I/O operations on other threads
+ * (including {@link #connect} with {@link IOException}.
+ * <li>Only one {@link TagTechnology} can be connected at a time. Other calls to
+ * {@link #connect} will return {@link IOException}.
+ * <li>I/O operations may block, and should never be called on the main application
+ * thread.
+ * </ul>
+ */
 public interface TagTechnology extends Closeable {
     /**
      * This technology is an instance of {@link NfcA}.
@@ -90,22 +145,22 @@ public interface TagTechnology extends Closeable {
     public static final int MIFARE_ULTRALIGHT = 9;
 
     /**
-     * Get the {@link Tag} object this technology came from.
+     * Get the {@link Tag} object backing this {@link TagTechnology} object.
+     * @return the {@link Tag} backing this {@link TagTechnology} object.
      */
     public Tag getTag();
 
     /**
-     * Opens a connection to the {@link Tag} enabling interactive commands. The command set
-     * varies by the technology type.
-     *
-     * <p>This method blocks until the connection has been established.
-     *
-     * <p>A call to {@link #close} from another thread will cancel a blocked call and cause an
-     * IOException to be thrown on the thread that is blocked.
+     * Enable I/O operations to the tag from this {@link TagTechnology} object.
+     * <p>May cause RF activity and may block. Must not be called
+     * from the main application thread. A blocked call will be canceled with
+     * {@link IOException} by calling {@link #close} from another thread.
+     * <p>Only one {@link TagTechnology} object can be connected to a {@link Tag} at a time.
+     * <p>Applications must call {@link #close} when I/O operations are complete.
      *
-     * @see #reconnect()
      * @see #close()
-     * @throws IOException if the target is lost, or connect canceled
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or connect is canceled
      */
     public void connect() throws IOException;
 
@@ -113,40 +168,34 @@ public interface TagTechnology extends Closeable {
      * Re-connect to the {@link Tag} associated with this connection. Reconnecting to a tag can be
      * used to reset the state of the tag itself.
      *
-     * <p>This method blocks until the connection is re-established.
-     *
-     * <p>A call to {@link #close} from another thread will cancel a blocked call and cause an
-     * IOException to be thrown on the thread that is blocked.
+     * <p>May cause RF activity and may block. Must not be called
+     * from the main application thread. A blocked call will be canceled with
+     * {@link IOException} by calling {@link #close} from another thread.
      *
      * @see #connect()
      * @see #close()
-     * @throws IOException
+     * @throws TagLostException if the tag leaves the field
+     * @throws IOException if there is an I/O failure, or connect is canceled
      * @hide
      */
     public void reconnect() throws IOException;
 
     /**
-     * Closes the connection to the {@link Tag}. This call is non-blocking and causes all blocking
-     * operations such as {@link #connect} to be canceled and immediately throw
-     * {@link java.io.IOException} on the thread that is blocked.
-     *
-     * <p>
-     * Once this method is called, this object cannot be re-used and should be discarded. Further
-     * calls to {@link #connect} will fail.
+     * Disable I/O operations to the tag from this {@link TagTechnology} object, and release resources.
+     * <p>Also causes all blocked I/O operations on other thread to be canceled and
+     * return with {@link IOException}.
      *
      * @see #connect()
-     * @see #reconnect()
      */
     public void close() throws IOException;
 
     /**
-     * Helper to indicate if {@link #connect} has succeeded.
-     * <p>
-     * Does not cause RF activity, and does not block.
-     * @return true if {@link #connect} has completed successfully and the {@link Tag} is believed
-     * to be within range. Applications must still handle {@link java.io.IOException}
-     * while using methods that require a connection in case the connection is lost after this
-     * method returns.
+     * Helper to indicate if I/O operations should be possible.
+     *
+     * <p>Returns true if {@link #connect} has completed, and {@link #close} has not been
+     * called, and the {@link Tag} is not known to be out of range.
+     * <p>Does not cause RF activity, and does not block.
+     * @return true if I/O operations should be possible
      */
     public boolean isConnected();
 }