[ntp:questions] Kernel PPS programs.

unruh unruh at invalid.ca
Wed Feb 8 17:45:50 UTC 2012

On 2012-01-21, Hal Murray <hal-usenet at ip-64-139-1-69.sjc.megapath.net> wrote:
> In article <X5nSq.1459$kp5.81 at newsfe18.iad>,
>  unruh <unruh at invalid.ca> writes:
>>Further to my kernel pps problems. I have now managed to get pps-ldisc
>>which is supposed to timestamp the serial port DCD transition interrupt,
>>and the pps_parport. In the case of the latter I was wondering if anyone
>>has any idea of how it works. The on board parallel port interface on
>>old motherboards used the edge transition to signal the interrupt. This
>>would mean that once the routine had serviced the interrupt, no other
>>one would occur until that next edge. However, for the add in parallal
>>cards, they use shareable, level triggered interrupts. Since the input pulse is
>>many ms long, this means that the interrupt keeps triggering about once
>>every usec as long as the ack line is up. 
>>Does anyone know if the pps_parport module treats such shareable
>>interrupts correctly?
> Usually, that sort of hardware has a way to turn off the interrupt.
> It's something like you write a bit in a register to "ACK" that
> interrupt.  When the external signal turns off, it clears that bit.
> The info should be in the fine print if you can get a good data sheet.

I have looked carefully, and can onlyfind a bit for turning off
interrupts (which of course does not turn on again). That would be fine
if it were edge triggered, but not for level triggered.


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