On Tue, 15 Sep 2020 13:04:15 +0100, The Natural Philosopher
 declaimed the following:


>Bugger. I really wanted to be in and around 25uS total time to service
>the interrupt.
>
>Kernel driver at least on i/o to achieve buffering to carry past that
>delay  looks needful..
>
>
...
>
>Hmm. So its either code device drivers to get speed, or code your own
>network drivers and write a minimal real time kernel.
>
>Many thanks for all that. It narrows the options down enough to be of
>use in deciding whether to use a pi at all.

 Perhaps you want to explore a Beaglebone Black, putting the interrupt
stuff on one of the two PRU-ICSS (Programmable Realtime Unit - Industrial
Communication SubSystem) modules. The PRU is basically a microcontroller
with a fixed instruction cycle time. It does not have what most would call
interrupts -- one has to poll the "interrupt bit".

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwip5ca
owevrAhVEbKwKHQItDsgQFjADegQIAhAB&url=https%3A%2F%2Felinux.org%2Fimages%2Fd%2Fd
a%2FAm335xPruReferenceGuide.pdf&usg=AOvVaw1ki8nYyvKFQ7P-YKGoD2QD
(note: there is now a C compiler for the PRU, that document is old enough
to only mention PASM)


--
 Wulfraed                 Dennis Lee Bieber         AF6VN
 wlfraed@ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/

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