SDCC's z80 crt0 sets SP=0x0000 and makes its first stack push at 0xFFFF.
The chip only mapped RAM at 0x8000-0xBFFF (0xC000+ was MMIO/ignored), so the
stack landed on unmapped memory and a plain C program crashed inside crt0 —
before main — which is why z80-led-chaser-c compiled but drove nothing.
Extend RAM to cover 0x8000-0xFFFF (32 KB) with the MMIO window 0xC000-0xC0FF
carved out and checked first, in scripts/make-z80-cpu.py + regenerated
z80-cpu.c. Now SDCC's default stack works and "write C from scratch, click
Run" just works — no manual `LD SP` needed (dropped from chaser.c). Bumped
the chip WASM initial memory to 4 pages to hold the larger RAM buffer. Larson
(asm, SP=0xBFFF, LED at 0xC000) is unaffected.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Adds the Zilog Z80 to the programmable-retro-CPU lineup. Same compile-rom
flow that landed for the 8080 in PR #189: write Z80 asm in a project
file, click Compile (backend assembles via in-tree two-pass asm-z80),
click Run, the chip emulator boots from the resulting ROM bytes.
Backend:
- backend/app/services/asmz80.py — two-pass Z80 assembler covering the
practical demo subset: LD r,n / r,r' / rp,nn / (nn),A / A,(nn) +
ALU r/n + INC/DEC + JP/JR/DJNZ/CALL/RET + PUSH/POP + IN/OUT +
EX/EXX + LDIR/LDDR/IM/NEG + RLCA/RRCA/RLA/RRA + the simple
ED-prefix variants. Not yet: CB-prefix bit ops, DD/FD index ops.
- rom_compile.py routes target=z80 through the new assembler.
Chip:
- frontend/src/components/customChips/examples/intel/z80-cpu.{c,chip.json}
Generated by scripts/make-z80-cpu.py from the existing z80.c emulator
(same clean-room implementation that passes ZEXDOC end-to-end). The
external pin/bus protocol is replaced with internal RAM + ROM + MMIO
for LED/BTN/UART. 35 KB WASM.
Example:
- /examples/z80-larson-scanner — Knight-Rider-style walking LED.
Demonstrates JR/DJNZ/RLCA which the 8080 can't run.
Plus a small Z80 smoke-test asm under scripts/.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
David Montero