Sorry for spelling mistake, it should be "250ns" instead of "250".
The PM timer is based on a 24 or 32 bits counter with a "3.579545 MHz" input signal bits. So the precision is around 1000/3.579545=280ns. Another issue is that it will wrap around about every 4s with 24 bits counter. Li, Aubrey <> wrote: > Liu, Jiang wrote: > >> Li, Aubrey <> wrote: >>> Bill.Holler wrote: >>> >>>>> Oh, oh..., that's right, we should use TSC. >>>>> But since we will support platform on which TSC is not reliable in >>>>> deep c-state, I suggest we use PM timer to make code a bit easier >>>>> to readable, :- >>>> >>>> Do you recommend the HPET timer or the ACPI PM timer as a >>>> reliable timer? We are currently investigating the HPET timer. >>>> >>> ACPI PM timer is already supported in the ACPICA. >>> Take a look at $(SRC)/uts/intel/io/acpica/hardware/hwtimer.c >>> PM timer is recommended in ACPI spec for deep c-state. >>> But I think both can be used as a reliable source. >> >> If so, PM timer should be a better choice because it's more >> standardized than HPET and PM timer with 250 precision should be >> enough for C-state. >> > > What 250 precision means here? > > Thanks, > -Aubrey
