Re: tricky challenge for getting round level-driven interrupt problem: help!

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Mer, 2005-05-04 at 21:58, Luke Kenneth Casson Leighton wrote:
>  i believe i get it: you raise a level-triggered interrupt which _stays_
>  raised until such time as your fifo is empty.

Bingo. It only goes away when the chip really has nothing left to say.

>  all - that sometimes (frequently, in fact - about 1 in every
>  50 times) it hasn't got round to clearing the level-driven
>  interrupt by the time we come out of the ARM ISR (!)

So you'll poll again and find there is no pending work to do.

>  hence the redesign to do alternate read-write-read-write, and making
>  reads exclusive of writes, etc.

and maybe even turn the IRQ off and use a timer if its slow and not
sensitive to latency.. ?

>  ... so - in your opinion, alan, is the old approach we had
>  actually _on_ the right lines?

level triggered IRQ does sort of expect the other end responds promptly
to be efficient as opposed to merely reliable.

>  also, are you going to ukuug in august, it being _in_
>  aberystwyth and all :)

Its not in Aberystwyth, but I might be. Its in Swansea 8)


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