[ECOS] how to handle missed interrupt issue?

Dave Milter davemilter@gmail.com
Fri Feb 6 11:48:00 GMT 2009

On Thu, Feb 5, 2009 at 9:29 PM, Paul D. DeRocco <pderocco@ix.netcom.com> wrote:
> @ix.netcom.com
>> From: Dave Milter
>> Some days ago I started development of ecos's driver for some device
>> which compatible with ARINC 429.
>> Processor is belong to ARM9 family, freq is 200Mhz.
>> The logic is simple. Driver has circular buffer, and when it receive
>> from device interrupt, which means that it ready
>> to go, driver send to device next 32bit word, then it recieves next
>> interrupt and send next word and so on.
>> When driver sends all characters from circular buffer, it start from
>> begining of buffer.
>> Now I want implement function to change circular buffer pointer,
>> but if I do such simple thing:
>> cyg_drv_isr_lock()
>> change pointer
>> cyg_drv_isr_unlock()
>> there is probability that I lost interrupt between cyg_drv_isr_lock()
>> and cyg_drv_isr_unlock(),
>> and this of cause a problem, I willl wait interrupt and it never happens.
>> I imagine such scheme:
>> isr handler each time call dsr handler (via return value),
>> dsr signal via condition variable about interrupt,
>> when I want to change pointer to circular buffer, I do
>> wait on condition variable, and then disable interrupt, change my
>> pointer and enable interrupt.
>> This will works, because of maximum bit rate  of ARINC 429 is 100Kb/s, and
>> before next interrupt I have many time to disable/enable interrupts.
>> But may be there is more clever way to handle such case?
> This shouldn't happen. Is it possible that your interrupt source generates a
> pulse, and your interrupt input is level-sensitive? That's a recipe for lost
> interrupts.
> I have no idea why you need to change the buffer pointer, but one
> alternative is to have the interrupt handler do that for you, in response to
> setting some request flag in the application.

you think that settting flag on arm9 is atomic thing?

I look at code atomic in linux kernel, in case of arm9 (armv5 core) it
disable interrupts
set flag and then enable interrupts.

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