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diff --git a/docs/html/ndk/guides/cpu-features.jd b/docs/html/ndk/guides/cpu-features.jd new file mode 100644 index 0000000..b031909 --- /dev/null +++ b/docs/html/ndk/guides/cpu-features.jd @@ -0,0 +1,210 @@ +page.title=The cpufeatures Library +@jd:body + +<div id="qv-wrapper"> + <div id="qv"> + <h2>On this page</h2> + + <ol> + <li><a href="#usage">Usage</a></li> + <li><a href="#functions">Functions</a></li> + <li><a href="#ch">Change History</a></li> + </ol> + </div> + </div> + +<p>The NDK provides a small library named {@code cpufeatures} that your app can use at runtime to +detect the target device's CPU family and the optional features it supports. It is designed to work +as-is on all official Android platform versions.</p> + +<h2 id="usage">Usage</h2> +<p>The {@code cpufeatures} library is available as an import module. To use it, follow the procedure +below:</p> + +<ol> +<li>List {@code cpufeatures} in your list of static library dependencies. For example: + +<pre class="no-pretty-print"> +LOCAL_STATIC_LIBRARIES := cpufeatures +</pre> +</li> + +<li>In your source code, include the {@code <cpu-features.h>} header file.</li> + +<li>At the end of your <a href="{@docRoot}ndk/guides/android_mk.html">{@code Android.mk}</a> file, +insert an instruction to import the {@code android/cpufeatures} module. For example: + +<pre class="no-pretty-print"> +$(call import-module,android/cpufeatures) +</pre> + +<p>Here is a simple example of an {@code Android.mk} file that imports the {@code cpufeatures} +library:</p> + +<pre class="no-pretty-print"> +<project-path>/jni/Android.mk: +LOCAL_PATH := $(call my-dir) + +include $(CLEAR_VARS) +LOCAL_MODULE := <your-module-name> +LOCAL_SRC_FILES := <your-source-files> +LOCAL_STATIC_LIBRARIES := cpufeatures +include $(BUILD_SHARED_LIBRARY) + +$(call import-module,android/cpufeatures) +</pre> +</li> +</ol> + +<h2 id="functions">Functions</h2> +<p>The {@code cpufeatures} library provides two functions. The first function returns the family to +which the device's CPU belongs. Declare it as follows:</p> + +<pre class="no-pretty-print"> +AndroidCpuFamily android_getCpuFamily(); +</pre> + +<p>The function returns one of the following enums, representing the CPU family/architecture that +the device supports.</p> +<ul> +<li>{@code ANDROID_CPU_FAMILY_ARM}</li> +<li>{@code ANDROID_CPU_FAMILY_X86}</li> +<li>{@code ANDROID_CPU_FAMILY_MIPS}</li> +<li>{@code ANDROID_CPU_FAMILY_ARM64}</li> +<li>{@code ANDROID_CPU_FAMILY_X86_64}</li> +<li>{@code ANDROID_CPU_FAMILY_MIPS64}</li> +</ul> + +<p>For a 32-bit executable on a 64-bit system, this function returns only the 32-bit value.</p> + +<p>The second function returns the set of optional features that the device's CPU supports. Declare +it as follows: + +<pre class="no-pretty-print"> +uint64_t android_getCpuFeatures(); +</pre> + +<p>The return value takes the form of a set of bit flags, each flag representing one +CPU-family-specific feature. The rest of this section provides information on features for +the respective families.</p> + +<h4>32-bit ARM CPU family</h4> + +<p>The following flags are available for the 32-bit ARM CPU family:</p> +<dl> +<dt>{@code ANDROID_CPU_ARM_FEATURE_VFPv2}</dt> +<dd>Indicates that the device's CPU supports the VFPv2 instruction set. Most ARMv6 CPUs support +this instruction set.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_ARMv7}</dt> +<dd>Indicates that the device's CPU supports the ARMv7-A instruction set as supported by the +<a href="{@docRoot}ndk/guides/abis.html#v7a">armeabi-v7a</a> ABI. This instruction set supports both +Thumb-2 and VFPv3-D16 instructions. This return value also indicates support for the VFPv3 hardware +FPU instruction-set extension.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_VFPv3}</dt> +<dd>Indicates that the device's CPU supports the VFPv3 hardware FPU instruction-set extension. +<p>This value is equivalent to the {@code VFPv3-D16} instruction set, which provides provides only +16 hardware double-precision FP registers.</p></dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_VFP_D32}</dt> +<dd> Indicates that the device's CPU supports 32 hardware double-precision FP registers instead of +16. Even when there are 32 hardware double-precision FP registers, there are still only 32 +single-precision registers mapped to the same register banks.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_NEON}</dt> +<dd>Indicates that the device's CPU supports the ARM Advanced SIMD (NEON) vector instruction set +extension. Note that ARM mandates that such CPUs also implement VFPv3-D32, which provides 32 +hardware FP registers (shared with the NEON unit).</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_VFP_FP16}</dt> +<dd>Indicates that the device's CPU supports instructions to perform floating-point operations on +16-bit registers. This feature is part of the VFPv4 specification.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_VFP_FMA}</dt> +<dd>Indicates that the device's CPU supports the fused multiply-accumulate extension for the VFP +instruction set. Also part of the VFPv4 specification.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_NEON_FMA}</dt> +<dd>Indicates that the device's CPU supports the fused multiply-accumulate extension for the NEON +instruction set. Also part of the VFPv4 specification.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_IDIV_ARM}</dt> +<dd>Indicates that the device's CPU supports integer division in ARM mode. Only available on later- +model CPUs, such as Cortex-A15.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_IDIV_THUMB2}</dt> +<dd>Indicates that the device's CPU supports Integer division in Thumb-2 mode. Only available on +later-model CPUs, such as Cortex-A15.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_iWMMXt}</dt> +<dd>Indicates that the device's CPU supports an instruction-set extension that adds MMX registers +and instructions. This feature is only available on a few XScale- based CPUs.</dd> + +<dt>{@code ANDROID_CPU_ARM_FEATURE_LDREX_STREX}</dt> +<dd>Indicates that the device's CPU supports LDREX and STREX instructions available since ARMv6. +Together, these instructions provide atomic updates on memory with the help of exclusive +monitor.</dd> +</dl> + +<h4>64-bit ARM CPU family</h4> + +<p>The following flags are available for the 64-bit ARM CPU family:</p> +<dl> +<dt>{@code ANDROID_CPU_ARM64_FEATURE_FP}</dt> +<dd>Indicates that the device's CPU has a Floating Point Unit (FPU). All Android ARM64 devices must +support this feature.</dd> +<dt>{@code ANDROID_CPU_ARM64_FEATURE_ASIMD}</dt> +<dd>Indicates that the device's CPU has an Advanced SIMD (ASIMD) unit. All Android ARM64 devices +must support this feature.</dd> +<dt>{@code ANDROID_CPU_ARM64_FEATURE_AES}</dt> +<dd>Indicates that the device's CPU supports {@code AES} instructions.</dd> +<dt>{@code ANDROID_CPU_ARM64_FEATURE_CRC32}</dt> +<dd>Indicates that the device's CPU supports {@code CRC32} instructions.</dd> +<dt>{@code ANDROID_CPU_ARM64_FEATURE_SHA1}</dt> +<dd>Indicates that the device's CPU supports {@code SHA1} instructions.</dd> +<dt>{@code ANDROID_CPU_ARM64_FEATURE_SHA2}</dt> +<dd>Indicates that the device's CPU supports {@code SHA2} instructions.</dd> +<dt>{@code ANDROID_CPU_ARM64_FEATURE_PMULL}</dt> +<dd>Indicates that the device's CPU supports 64-bit {@code PMULL} and {@code PMULL2} +instructions.</dd> +</dl> + +<h4>32-bit x86 CPU family</h4> + +<p>The following flags are available for the 32-bit x86 CPU family.<p> +<dl> +<dt>{@code ANDROID_CPU_X86_FEATURE_SSSE3}</dt> +Indicates that the device's CPU supports the SSSE3 instruction extension set.</dd> + +<dt>{@code ANDROID_CPU_X86_FEATURE_POPCNT}</dt> +<dd>Indicates that the device's CPU supports the {@code POPCNT} instruction.</dd> + +<dt>{@code ANDROID_CPU_X86_FEATURE_MOVBE}</dt> +<dd>Indicates that the device's CPU supports the {@code MOVBE} instruction. This instruction is +specific to some Intel IA-32 CPUs, such as Atom.</dd> +<dl> + +<p>{@code android_getCpuFeatures()} returns {@code 0} for CPU families for which there are no +listed extensions.</p> + +<p>The following function returns the maximum number of CPU cores on the target device: </p> + +<pre class="no-pretty-print"> +int android_getCpuCount(void); +</pre> + +<h4>MIPS CPU family</h4> + +<dl> +<dt>{@code ANDROID_CPU_MIPS_FEATURE_R6}</dt> +<dd>Indicates that the CPU executes MIPS Release 6 instructions natively, and supports obsoleted R1..R5 instructions only via kernel traps.</dd> + +<dt>{@code ANDROID_CPU_MIPS_FEATURE_MSA}</dt> +<dd>Indicates that the CPU supports MIPS SIMD Architecture instructions.</dd> +</dl> + +<h2 id="ch">Change History</h2> +<p>For the complete change history of this library, see the comments in +{@code $NDK/sources/android/cpufeatures/cpu-features.c}, where {@code $NDK} is the root of your +NDK installation.</p>
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