* George Spelvin <li...@horizon.com> wrote:
> Ingo Molnar wrote:
> > - Alternatively, I also tried a different method: to set up the RTC
> > periodic IRQ during early boot, but not have an IRQ handler, polling
> > RTC_PF in the rtc_cmos_read(RTC_INTR_FLAGS) IRQ status byte.
> >
> > Unfortunately when I do this then PIO based RTC accesses can take
> > tens of thousands of cycles, and the resulting jitter is pretty bad
> > and hard to filter:
>
> Did you use rtc_cmos_read()? [...]
Yeah, so initially I did, but then after I noticed the overhead I introduced:
+unsigned char rtc_cmos_read_again(void)
+{
+ return inb(RTC_PORT(1));
+}
+
which compiles to a single INB instruction.
This didn't change the delay/cost behavior.
The numbers I cited, with tens of thousands of cycles per iteration, were from
such an optimized poll loop already.
Thanks,
Ingo
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