On Mon, 12 May 2008 09:33:54 -0700 Colin D Bennett <[EMAIL PROTECTED]> wrote:
> I think that using the TSC (w/ RDTSC instruction) and calibrating it
> with a quick 2-3 RTC tick loop at startup might be the easiest option.
Just wondered if something like this would be a practical way to go:
/*******************************************************************/
/* How many ticks to use for calibration loop. (>= 1) */
#define CALIBRATION_TICKS 2
/* Output: Number of TSC cycles per second. */
grub_uint64_t tsc_cycles_per_second;
void grub_timer_tsc_calibrate(void)
{
/* Calibrate to real time (relative, not absolute). */
grub_uint64_t start_tsc;
grub_uint64_t end_tsc;
grub_uint32_t initial_tick;
grub_uint32_t start_tick;
grub_uint32_t end_tick;
/* Wait for the start of the next tick;
we'll base out timing off this edge. */
initial_tick = grub_get_rtc();
do
{
start_tick = grub_get_rtc();
}
while (start_tick == initial_tick);
start_tsc = rdtsc();
/* Wait for the start of the next tick. This will
be the end of the 1-tick period. */
do
{
end_tick = grub_get_rtc();
}
while (end_tick - start_tick < CALIBRATION_TICKS);
end_tsc = rdtsc();
tsc_cycles_per_second =
(end_tsc - start_tsc) / (end_tick - start_tick)
* GRUB_TICKS_PER_SEC;
}
/*******************************************************************/
Colin
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