Programmable Interval Timer

[Astaelan]

A Programmable Interval Timer device abstraction that supports at least 1MS precision callbacks. Must follow the unified device driver model described by issue #4.

Must support the following:

• PIT Base Class (100% Complete)
• Millisecond Caching (100% Complete)

Must provide support for the following system calls:

• sleep (Postponed)
• usleep (Postponed)
• gettimeofday (100% Complete)

[retep998]

Ideally we should get at least 0.1 ms precision. Windows 7 uses exactly 1 ms precision, so we need to at least be better at timing.

[Astaelan]

At 1ghz, 1 instruction takes about 1 nanosecond. 0.1 millisecond = 100 microseconds 1 microsecond = 1000 nanoseconds For 100 microsecond precision, we have approximately 100,000 instructions between interrupts on a 1ghz. On a better 3ghz, approximately 300,000 instructions between interrupts. On a lesser 200mhz, approximately 20,000 instructions between interrupts. This level of granularity is acceptable, but should be carefully tested for approximate cost of the interruption handler.

[Astaelan]

Most of the functionality is now working, support for sleep potentially requires code that will be dealt with later for hardware threading.

[Astaelan]

Postponing sleep and usleep until a later point when threading model can be determined.