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SubjectRe: Microsecond resolution timers - final word
Hi David.

>>> Incidentally, the dos version does its timing using the
>>> hardware timer at 0x40-0x5f...

>> Presumably via a driver that plugs itself in there, then resets
>> the timer to spin faster and only passes through every 100th (or
>> whatever) tick to the routine behind it...

> RTLinux periodic scheduler... Unless you absolutely refuse to
> use it! ;-)

Not up to me - I'm not the one in need of it. RedHat 6.0 upgraded to
kernel 2.2.10 does everything I currently need...

>>> ...though I don't think I'm allowed to do that.

>> Nope, but you might wish to have a look at the various patches
>> that raise Linux's HZ rate as those also allow suchlike
>> increases to take place in a compatible manner...

> Hmmm... So we're patching the kernel anyway... Why not do it
> real, and get solid, reliable timing as an extra bonus? :-)

The patches in question are NOT currently under consideration for the
distribution kernel, at least not as I understand it. Basically,
various people have implemented various patches that enable the kernel
HZ rate to be set to various speeds other than 100 Hz, and have made
their patches available for downloading on various sites. However, as
I understand it, the various patches are (A) incompatible with each
other, and (B) largely untested other than by the author.

However, I understand that those patches have brought to light certain
other kernel problems which have been fixed as a result...

Best wishes from Riley.

| There is something frustrating about the quality and speed of Linux |
| development, ie., the quality is too high and the speed is too high, |
| in other words, I can implement this XXXX feature, but I bet someone |
| else has already done so and is just about to release their patch. |

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