~maddie/custom-processor-specification

d53e95f29fc140fa2c2057c1b01ee78e5e99edfc — Madeline Cronin 3 months ago 88e7a2f master
Clarified program counter behaviour.
1 files changed, 5 insertions(+), 3 deletions(-)

M ISA_spec.txt
M ISA_spec.txt => ISA_spec.txt +5 -3
@@ 1,4 1,4 @@
Maddie's test ISA Version 1.0.9
Maddie's test ISA Version 1.0.10


Table of contents:


@@ 25,7 25,8 @@ also a 2 bit flags register for storing the condition flags.
Behaviours: The only statefulness not directly controlled by programs is the
interrupt toggle. Numbers are read as big endian. Hardware interrupts jump to
zero, and push the prior program counter to the stack. Unknown opcodes are
treated as a halt.
treated as a halt. The program counter increments by 2 after every instruction
except control flow, with no alignment checks.

Versioning: The versioning of this ISA follows semantic versioning, although
given how many breaking changes it is likely to go though, the major version


@@ 125,7 126,8 @@ XXX=
001: Read/write main memory
010: R/W disk
011: R/W VRAM
100: R/W to serial port
100: R/W to serial port, using only the lower 8 bits of a value, setting the
upper 8 bits to 0 on a read.

Immediate value:
----0110|RRRRR---|xxxxxxxx|xxxxxxxx