[ntp:questions] Kernel PPS programs.

unruh unruh at invalid.ca
Tue Jan 24 18:30:50 UTC 2012


On 2012-01-24, DaveB <g8kbv at uko2.co.uk> wrote:
> In article <VUBSq.3384$%x7.3294 at newsfe10.iad>, unruh at invalid.ca says...
>> > 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.
>> 
>> >
>
> When you program that I/O bit to "turn off" interupts on that port, it 
> probably clears a latch too, so that it is ready for the next change in 
> input level to trigger another IRQ.
>
> See if you can find some original IBM PC schematics and bios listings on 
> t'interweb somewhere.  We all learnt a lot back in the day from them.

The problem is that these parallel cards are different from the original
parallel cards. There use level triggered interrupts so that they can
share interrupts with other devices. The PC parallel used edge triggered
interrupts which also were unsharable. 

A sharable interrupt should allow you to switch off the interrupt until
the clear edge occurs, at which point the interrupt should switch on
again. 


>
> Just about all the plugin cards and adapters since then, were designed 
> to behave in much the same way, if not using the same circuitry, just 
> integrated all into one small bit of plastic.

Nope. they are not. They use totally different interrupt numbers, and
logic. 

>
> Have Fun.
>
> Dave B.
>
> PS:	Anyone remember Data General's "Busy" and "Done" flags?



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