[addaon]

> The reason why the PC is not normally exposed as a regular register is that the set of operations needed for the PC is different than for the regular registers.

I'd add to that, that what you give is the reason it's /okay/ to expose the PC as a special register instead of a GPR. The reason that it's /important/ to is that the PC is accessed on every instruction fetch, so if it's part of a uniform register file, it basically eats up an entire read port of that register file. Register file size scaled badly with port count (much worse than it does with register count), so this ends up adding quite a bit of area. (You can hack around this by having a single dedicated read port for just the PC register, but then you're half way to an SPR.)

[dfox]

It does not make sense to dedicate full read port for reading PC. Just run a bus directly from the register cells, which is exactly how it is done in ARM7TDMI in question.

[addaon]

Sure, but then you're half way to a special purpose register. And then you get to add in the logic to arbitrate writes from the GPR ports with reads from the PC-dedicated port. At which point you have more hardware complexity than just a dedicated SPR.