S12 / MagniV MicrocontrollersのトピックXGATE ISR size question

XGATE ISR size question

roberthiebert — Mon, 03 Nov 2025 17:15:27 GMT

From what I've read in the manuals and application notes, XGATE is designed to service ISRs to take some load off of the CPU. It also states that these ISRs should be kept as short as possible, so I have 2 questions.

First, how short is short? Is there a guide line for the number of instructions that the ISR should be limited to?

Second, why is it necessary to keep these ISRs short, and what happens if they get too long?

Regards,

Robert

Re: XGATE ISR size question

kef2 — Tue, 04 Nov 2025 07:23:55 GMT

That's just a standard to make Interrupt Service Routines taking as short as possible. ISR's taking longer lead to longer interrupt latency and other potential application issues.
Smaller code often means faster code (small loopy code of some may take very long).
XGATE ISR code is limited by XGATE memory space, which is 64k.
Regarding shortness of ISR, you may decide to not use XGATE interrupts at all and instead trigger one (software) interrupt and never exit from its ISR.