Re: What is an N-bit machine?

On 11/30/24 3:38 PM, Michael S wrote:

On Sat, 30 Nov 2024 19:40:17 -0000 (UTC)
John Levine <johnl@taugh.com> wrote:

[snip]

I get the impression that we will have 32 bit architectures for a very
long time, since they are smaller and cheaper to implement than 64 bit
and for a lot of embedded applications they are more than adequate.
Examples are ARM Cortex-R4 and -R5, high performance 32 bit realtime
chips.
>

 I agree with conclusions, but not with your examples.
IMHO, the whole ARM Cortex-R series is solution looking for problem. It
could be quite easily replaced by 64-bit A series cores.
Now Cortex-M is completely different story. Here 64-bit cores would not
be appropriate.

I wonder if a 32-bit version of AArch64 would have been
appropriate for the Cortex-R series. The area and power difference
might not have been sufficient to justify "backporting" AArch64 to
32-bit. In addition to the extra development costs, providing yet
another 32-bit architecture would have introduced marketing costs
not only to communicate the tradeoffs for the new products but
also to provide confidence that the M series will not be
abandoned.
Power and code density (and even cost) might not be _as_ important
for the R series as for the M series, so AArch64 might well have
been a reasonable fit.
I have never worked on embedded systems and never even closely
followed the market, but thinking about the tradeoffs can be fun.