Re: [lwip-users] Required accuracy of timers

[H. Peter Anvin]

Jonathan Larmour wrote:
> In practice I don't think there are any timers which require better than
> 100ms granularity, and I doubt a little inaccuracy delaying a timeout by up
> to 55ms would really affect much (as long as it isn't up to 55ms _early_).
>
> Although in any case, PC hardware is actually pretty standard - with
> backward compatibility still present for obscenely ancient devices. Usually
> you can use the Periodic Interval Timer anywhere. You can see a usage
> example in eCos here(hal_pc_clock_initialize and hal_pc_clock_read):
> http://ecos.sourceware.org/cgi-bin/cvsweb.cgi/ecos/packages/hal/i386/pcmb/current/src/pcmb_misc.c?rev=1.9&content-type=text/x-cvsweb-markup&cvsroot=ecos
> with some info from:
> http://ecos.sourceware.org/cgi-bin/cvsweb.cgi/ecos/packages/hal/i386/pcmb/current/include/pcmb_intr.h?rev=1.5&content-type=text/x-cvsweb-markup&cvsroot=ecos
>
> It uses interrupt IRQ0 i.e. 32.

IRQ 0 is INT 8 in the BIOS environment, not 32.

And yes, PC hardware is pretty standard... but there isn't a whole lot 
of arbitration (who owns what resources) in the pre-OS environment.  As 
such, you risk finding something else trying to play the same tricks.

Once the OS boots, the OS is resource manager, and that particular 
problem doesn't exist in the same way.

Sounds like 55 ms is adequate resolution, so doing more advanced PIT 
hackage is probably not necessary.

        -hpa