The 4040 is a binary-compatible superset of the 4004. This commit:
- Adds the full 4004 ISA into 4040.c (LD/XCH/INC/ADD/SUB/JCN/JUN/
JMS/BBL/FIM/FIN/JIN/SRC/ISZ/LDM/I-O/ACC group/DAA/KBP/etc.) so the
4040 actually executes user code, not just NOPs.
- Adds the 14 4040-only opcodes per MCS-40 p. 1-22 at OPR=0000
OPA=0x01..0x0E:
HLT, BBS, LCR, OR4, OR5, AN6, AN7, DB0, DB1, SB0, SB1, EIN, DIN,
RPM (4289 stub).
- Implements bank-aware register access — physical reg[0..7] is
bank 0's R0..R7, reg[8..15] is shared R8..R15, reg[16..23] is
bank 1's R0..R7. SB0/SB1 toggle the active R0..R7 mapping.
- 7-deep PC stack (vs 4004's 3-deep) per MCS-40 p. 1-12.
- Interrupt vectoring already in place from prior commit; BBS now
pops PC and clears INTA.
3 it.todo tests promoted to passing:
- INT high after EIN vectors PC to 0x003 and asserts INTA.
- BBS pops PC and clears INTA.
- SB1 + FIM writes to bank-1 R0..R7 (verified by ISZ wrap behaviour:
bank-0 R0=F → ISZ wraps to 0 → no branch, distinguishing from a
buggy SB1 that would have aliased the write to bank 0).
Adds Bus4040 helper (parallel to Bus4004) for feeding opcodes via
the multiplexed nibble bus. Total test_intel: 55 passing (was 52),
0 failed, 22 todo.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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