Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Robert Finch <robfi680@gmail.com>
Newsgroups: comp.arch
Subject: Re: MSI interrupts - Instructions
Date: Wed, 26 Mar 2025 06:56:00 -0400
Organization: A noiseless patient Spider
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In-Reply-To: <vrf712$1h233$1@dont-email.me>

Working on a simple OS I thought it might be useful to be able to poll 
for interrupts when interrupts are disabled. I think there may be times 
where it is acceptable to process certain kinds of interrupts even if 
they were disable. So, I added a poll-for-interrupt instruction to the 
architecture. Which just checks for interrupts and continues if there is 
not one. I have seen wait-for-interrupt instructions before, but not 
sure about polling.

I also added a two-up-level return from interrupt instruction. I have 
not seen this in other architectures, but I needed it at one point. 
Interrupt information is stored on an internal stack, and it is tricky 
(slow) to manipulate it for a two-up-level return. It is an eight level 
stack with two or three words of information per level. It was a bit 
much to copy it all in software, so I added the hardware return. But it 
is a lot of extra hardware for a very rare occurrence.

Finding this discussion on interrupts informative. I have only done a 
modicum of work on an OS; tried to get things working with spinlocks.