Re: register sets

On Wed, 16 Apr 2025 23:42:20 -0400, Robert Finch wrote:

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.

I had to re-read this to understand it.

Some architectures in the past did speed up context-switching between
user programs and the operating system by giving the operating system
its own set of registers.

And the operating system doesn't need to do floating-point math, only
user programs that do calculations. So what could go wrong with this
great idea?

The first thing that comes to mind is that even a computer with a GUI,
not merely a time-sharing mainframe, may have multiple user programs
running at once. So when a real-time clock interrupt hits, and it's
time to rotate from one compute-bound user program to another, those
floating-point registers *also* need to be saved to memory.

So you will probably need an outer ring of the OS that doesn't use
the special OS-specific set of registers.

John Savard