diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/00-INDEX | 2 | ||||
| -rw-r--r-- | Documentation/timers/00-INDEX | 10 | ||||
| -rw-r--r-- | Documentation/timers/hpet.txt (renamed from Documentation/hpet.txt) | 43 |
3 files changed, 31 insertions, 24 deletions
diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX index 7306081..4382778 100644 --- a/Documentation/00-INDEX +++ b/Documentation/00-INDEX @@ -159,8 +159,6 @@ hayes-esp.txt - info on using the Hayes ESP serial driver. highuid.txt - notes on the change from 16 bit to 32 bit user/group IDs. -hpet.txt - - High Precision Event Timer Driver for Linux. timers/ - info on the timer related topics hw_random.txt diff --git a/Documentation/timers/00-INDEX b/Documentation/timers/00-INDEX new file mode 100644 index 0000000..397dc35 --- /dev/null +++ b/Documentation/timers/00-INDEX @@ -0,0 +1,10 @@ +00-INDEX + - this file +highres.txt + - High resolution timers and dynamic ticks design notes +hpet.txt + - High Precision Event Timer Driver for Linux +hrtimers.txt + - subsystem for high-resolution kernel timers +timer_stats.txt + - timer usage statistics diff --git a/Documentation/hpet.txt b/Documentation/timers/hpet.txt index 6ad52d9..e7c09ab 100644 --- a/Documentation/hpet.txt +++ b/Documentation/timers/hpet.txt @@ -1,21 +1,32 @@ High Precision Event Timer Driver for Linux -The High Precision Event Timer (HPET) hardware is the future replacement -for the 8254 and Real Time Clock (RTC) periodic timer functionality. -Each HPET can have up to 32 timers. It is possible to configure the -first two timers as legacy replacements for 8254 and RTC periodic timers. -A specification done by Intel and Microsoft can be found at -<http://www.intel.com/technology/architecture/hpetspec.htm>. +The High Precision Event Timer (HPET) hardware follows a specification +by Intel and Microsoft which can be found at + + http://www.intel.com/technology/architecture/hpetspec.htm + +Each HPET has one fixed-rate counter (at 10+ MHz, hence "High Precision") +and up to 32 comparators. Normally three or more comparators are provided, +each of which can generate oneshot interupts and at least one of which has +additional hardware to support periodic interrupts. The comparators are +also called "timers", which can be misleading since usually timers are +independent of each other ... these share a counter, complicating resets. + +HPET devices can support two interrupt routing modes. In one mode, the +comparators are additional interrupt sources with no particular system +role. Many x86 BIOS writers don't route HPET interrupts at all, which +prevents use of that mode. They support the other "legacy replacement" +mode where the first two comparators block interrupts from 8254 timers +and from the RTC. The driver supports detection of HPET driver allocation and initialization of the HPET before the driver module_init routine is called. This enables platform code which uses timer 0 or 1 as the main timer to intercept HPET initialization. An example of this initialization can be found in -arch/i386/kernel/time_hpet.c. +arch/x86/kernel/hpet.c. -The driver provides two APIs which are very similar to the API found in -the rtc.c driver. There is a user space API and a kernel space API. -An example user space program is provided below. +The driver provides a userspace API which resembles the API found in the +RTC driver framework. An example user space program is provided below. #include <stdio.h> #include <stdlib.h> @@ -286,15 +297,3 @@ out: return; } - -The kernel API has three interfaces exported from the driver: - - hpet_register(struct hpet_task *tp, int periodic) - hpet_unregister(struct hpet_task *tp) - hpet_control(struct hpet_task *tp, unsigned int cmd, unsigned long arg) - -The kernel module using this interface fills in the ht_func and ht_data -members of the hpet_task structure before calling hpet_register. -hpet_control simply vectors to the hpet_ioctl routine and has the same -commands and respective arguments as the user API. hpet_unregister -is used to terminate usage of the HPET timer reserved by hpet_register. |