21 Jul
2016
21 Jul
'16
11:34 p.m.
Liam Proven writes:
Peter Corlett wrote:
It's not. Peter is talking about a four-bit field in the instructions.
You're talking about a six-bit field in the program counter.
In ARM, *all* instructions can be predicated.
Because instructions
are 32 bits wide, it has the luxury of allocating four bits to select
from one of 16 possible predicates based on the CPU flags.
If I understand it correctly, this caused considerable problems for
the RISC OS people later. The original Acorn ARM machines used 26 bits
of the program counter as the PC, and the rest as flags.
I'm not sure this is the same phenomenon you're describing.