Re: How to handle very fast repeating interrupts?

["Martin Laabs" <martin.laabs@mailbox.tu-dresden.de>]

Hi,

On Mon, 16 Feb 2009 13:48:22 +0100, Chris Zimman <czimman@bloomberg.com> wrote:

>> Is the FIQ interrupt disabled while scheduling? (And if so - is it
>> disabled that long time?) I hope it isn't ...
>> The only RT requirement is to read the data from the memory bus
>> 12us after the interrupt at the latest. The processing afterwards
>> can be done in non-RT.
>
> Interrupts have to be disabled while you're in an ISR, and since the
> scheduler is typically driven from a timer interrupt, you are going to run
> into that.

There is an option to allow nested interrupts. Since the FIQ priority
is higher than that of the timer (typical priority 0) it would interrupt
it.

> Not being familiar with your project, I can't really say, but if I were to
> design something that needed this level of RT performance, I would probably
> use a faster processor or a small CPLD/FPGA to help with the data
> acquisition.

There is a cpld already do deserialize the data. However - it has not enought
flipflops/macrocells to provide a buffer. (And no external or dualport memory.)

I will try the FIQ and nested interrupt aproach this evening and report the
results.

Greetings,
 Martin L.