When is more than one PIT needed?

Hello,

I need to be able to put a process to sleep for 100-1000 microseconds 
(until now, I've been using a generic Linux kernel on a low-voltage x86 
CPU). AFAIU, the x86 platform comes with several timers[*] and I had 
hoped one of them would prove useful in my situation.

[*] I tried to list all the timers in:
http://groups.google.com/group/comp.arch/msg/6be4741f4f92be6
(I found PIT, RTC, (L?)APIC timer, ACPI timer, HPET, TSC.)

At some point, I was convinced that the simplest solution would be to 
purchase a PCI card with multiple Programmable Interval Timers, such as 
ADLINK's PCI-8554:

http://www.adlinktech.com/PD/web/PD_detail.php?pid=27

Then I ran into the relatively new hrtimers infrastructure[*] which 
seems to let me do what I need. (I'm not sure how, though.)

[*] http://www.tglx.de/hrtimers.html

I'm confused. It seems a generic Linux kernel can indeed provide 
high-resolution timers without any additionnal hardware.

Then when is a card with multiple PITs needed? Have any of you ever been 
in a situation where software came up short, and the multiple PITs were 
mandatory? What are the typical uses of such a card?

Regards.

Spoon wrote:

> I need to be able to put a process to sleep for 100-1000 microseconds 
> (until now, I've been using a generic Linux kernel on a low-voltage x86 
> CPU). AFAIU, the x86 platform comes with several timers[*] and I had 
> hoped one of them would prove useful in my situation.
> 
> [*] I tried to list all the timers in:
> http://groups.google.com/group/comp.arch/msg/6be4741f4f92be6
> (I found PIT, RTC, (L?)APIC timer, ACPI timer, HPET, TSC.)
> 
> At some point, I was convinced that the simplest solution would be to 
> purchase a PCI card with multiple Programmable Interval Timers, such as 
> ADLINK's PCI-8554:
> 
> http://www.adlinktech.com/PD/web/PD_detail.php?pid=27
> 
> Then I ran into the relatively new hrtimers infrastructure[*] which 
> seems to let me do what I need. (I'm not sure how, though.)
> 
> [*] http://www.tglx.de/hrtimers.html
> 
> I'm confused. It seems a generic Linux kernel can indeed provide 
> high-resolution timers without any additionnal hardware.
> 
> Then when is a card with multiple PITs needed? Have any of you ever been 
> in a situation where software came up short, and the multiple PITs were 
> mandatory? What are the typical uses of such a card?

Perhaps there is a more appropriate newsgroup for this query?

On Tue, 05 Sep 2006 16:31:25 +0200, Spoon <root@127.0.0.1> wrote:

This may not be what you want but you might want to look at rtai
linux. It's basically a real time kernel with linux riding on top. I
assume you are working on one of the small board form factor  pentium
2 or up?

Wulf wrote:

> I assume you are working on one of the small board form factor
> pentium 2 or up?

You assume correctly.

(Low-voltage Pentium 3 in a �ATX motherboard.)