Hi
On Thu, Jan 8, 2009 at 9:43 PM, Bruce Rowen <bro...@aoc.nrao.edu> wrote:
> Hello,
>
> I've been deferring a problem I ran into a few months back and I figure a
> new year is a good time to readdress it.
>
> I have a loadable module that controls some hardware. Within this hardware
> are various bits that need to be strobed (i.e set for a minimum specified
> time and then reset). I have several ioctl() functions set to do this, but
> when I tried using a usleep() to force a minimum delay, the system hanged. I
> did a work around by using the CPU internal register timer rdtscl(), but
> this has the side effect of tying up the CPU instead of allowing a
> reschedule as (hopefully) a usleep() would do.
>
> An example of what I'd like to do is:
>
> ...
>
> case STROBE_RESET:
> {
> hwRegister |= RESET_MASK;
> usleep (10000L); // hold bit high for at least 10ms
> hwRegister &= ~RESET_MASK;
> break;
> }
> ...
>
>
> Some delays are shorter (i.e. 20us).
>
> What (if any) taboos exist for using sleep() in a kernel ioctl call and what
> alternatives exist?
it's not a taboo. In your case, i think it's simply because you can
not reschedule because it will screw something (are you holding a lock
or something? probably some sequences of inb/outb must be done in
sequence ?). If yes, then busy wait is probably your only way to
delay.
> Kernel is 2.6.13 w/preemption, soon to be moving to a later version,
regards,
Mulyadi.
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