From d53e95f29fc140fa2c2057c1b01ee78e5e99edfc Mon Sep 17 00:00:00 2001 From: Madeline Cronin Date: Sun, 8 Sep 2024 14:06:48 +0100 Subject: [PATCH] Clarified program counter behaviour. --- ISA_spec.txt | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/ISA_spec.txt b/ISA_spec.txt index a12a8da..f208690 100644 --- a/ISA_spec.txt +++ b/ISA_spec.txt @@ -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 -- 2.43.4