static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap)
{
int count;
- u64 tsc = 0;
+ u64 tsc = 0, prev_tsc = 0;
for (count = 0; count < 50000; count++) {
if (!pit_verify_msb(val))
break;
+ prev_tsc = tsc;
tsc = get_cycles();
}
- *deltap = get_cycles() - tsc;
+ *deltap = get_cycles() - prev_tsc;
*tscp = tsc;
/*
* How many MSB values do we want to see? We aim for
* a maximum error rate of 500ppm (in practice the
* real error is much smaller), but refuse to spend
- * more than 25ms on it.
+ * more than 50ms on it.
*/
-#define MAX_QUICK_PIT_MS 25
+#define MAX_QUICK_PIT_MS 50
#define MAX_QUICK_PIT_ITERATIONS (MAX_QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256)
static unsigned long quick_pit_calibrate(void)
*
* As a result, we can depend on there not being
* any odd delays anywhere, and the TSC reads are
- * reliable (within the error). We also adjust the
- * delta to the middle of the error bars, just
- * because it looks nicer.
+ * reliable (within the error).
*
* kHz = ticks / time-in-seconds / 1000;
* kHz = (t2 - t1) / (I * 256 / PIT_TICK_RATE) / 1000
* kHz = ((t2 - t1) * PIT_TICK_RATE) / (I * 256 * 1000)
*/
- delta += (long)(d2 - d1)/2;
delta *= PIT_TICK_RATE;
do_div(delta, i*256*1000);
printk("Fast TSC calibration using PIT\n");