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libpayload: Change the measurement interval for get_cpu_speed to 2 ms. 

The interval used to be about 55 ms which is excessively long. Coreboot only
waits for 2 ms and gets a reasonable answer. That should be good enough for us
as well.

Change-Id: I4d4e8b25b6ba540c9e9839ed0bbaa1f04f67cce1
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: http://review.coreboot.org/2520
Tested-by: build bot (Jenkins)
Reviewed-by: Anton Kochkov <anton.kochkov@gmail.com>
This commit is contained in:
Gabe Black 2012-11-21 01:01:50 -08:00 committed by Anton Kochkov
parent 502533f656
commit b4523bb691
1 changed files with 9 additions and 7 deletions
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16
payloads/libpayload/arch/x86/timer.c
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@ -49,6 +49,8 @@ u32 cpu_khz;
unsigned int get_cpu_speed(void)
{
unsigned long long start, end;
const uint32_t clock_rate = 1193182; // 1.193182 MHz
const uint16_t interval = (2 * clock_rate) / 1000; // 2 ms
/* Set up the PPC port - disable the speaker, enable the T2 gate. */
outb((inb(0x61) & ~0x02) | 0x01, 0x61);
@ -56,9 +58,9 @@ unsigned int get_cpu_speed(void)
/* Set the PIT to Mode 0, counter 2, word access. */
outb(0xB0, 0x43);
/* Load the counter with 0xffff. */
outb(0xff, 0x42);
outb(0xff, 0x42);
/* Load the interval into the counter. */
outb(interval & 0xff, 0x42);
outb((interval >> 8) & 0xff, 0x42);
/* Read the number of ticks during the period. */
start = rdtsc();
@ -66,11 +68,11 @@ unsigned int get_cpu_speed(void)
end = rdtsc();
/*
* The clock rate is 1193180 Hz, the number of milliseconds for a
* period of 0xffff is 1193180 / (0xFFFF * 1000) or .0182.
* Multiply that by the number of measured clocks to get the kHz value.
* The number of milliseconds for a period is
* clock_rate / (interval * 1000). Multiply that by the number of
* measured clocks to get the kHz value.
*/
cpu_khz = (unsigned int)((end - start) * 1193180U / (1000 * 0xffff));
cpu_khz = (end - start) * clock_rate / (1000 * interval);
return cpu_khz;
}