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From: Robert Finch <robfi680@gmail.com>
Newsgroups: comp.arch
Subject: Re: register sets
Date: Wed, 16 Apr 2025 23:42:20 -0400
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Working on the Qupls3/StarkCPU core it looks like there will be enough 
resources to support two sets of registers. The extra set of registers 
comes for free for the register file as the BRAMs can support them. The 
only increase is in the RAT. The issue I have to trade-off on now is 
which of the four operating modes gets its own set of registers while 
the other three share a set. However, the first eight registers will be 
shared between all modes so that arguments can be passed between them. 
The ARM does this. My thought is that the application /  user  mode gets 
its own register set, and the rest of the system shares the other set. 
That way there is no need to save and restore the app registers when 
calling the system.

Another thought is to not include float registers for anything other 
than apps. It would save 32 regs per mode, possibly allowing three 
register sets to be provided.