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H8/536 ROM Decompiler

This repo now includes a standalone Python helper for the H8/536 ROM image:

python h8536_decompiler.py ROM\M27C512@DIP28_1.BIN --out build\rom_decompiled.asm --json build\rom_decompiled.json

If you are using the repo-local venv:

.\.venv\Scripts\python.exe h8536_decompiler.py --out build\rom_decompiled.asm --json build\rom_decompiled.json --cycles --callgraph-dot build\callgraph.dot

What It Does

  • Decodes the H8/500 instruction set used by the H8/536.
  • Reads the H8/536 minimum-mode vector table from the ROM.
  • Recursively traces reachable code from reset, interrupt, and trap vectors.
  • Emits labels for branch and call targets.
  • Tracks LDC.B #xx, BR along traced control flow so later short absolute @aa:8 operands can resolve automatically.
  • Annotates H8/536 register accesses such as P1DDR, SYSCR1, WCR, watchdog, timer/SCI/A-D, and RAM-control registers.
  • Decodes register bitfields and selected hardware semantics for setup writes.
  • Emits memory-region metadata for vector, DTC, RAM, register-field, and mode-dependent program/external space.
  • Parses the DTC vector table described by the manual.
  • Scans unreached ROM ranges for ASCII strings and pointer-table candidates.
  • Emits function summaries and a direct-call graph in JSON, with optional Graphviz DOT output.
  • Adds Appendix A cycle estimates to JSON and can append them to ASM comments.
  • Handles the E-clock transfer instructions MOVFPE and MOVTPE.

The generated listing is written to:

build/rom_decompiled.asm

The optional JSON output is useful for scripts or later analysis:

build/rom_decompiled.json

Useful Options

python h8536_decompiler.py --help
  • --mode min|max: vector format. This ROM appears to be minimum mode; min is the default.
  • --entry H'1234: add an extra entry point to recursive tracing.
  • --linear: linear-sweep the selected range instead of tracing from vectors.
  • --start H'1000 --end H'D100: constrain the decode range.
  • --br H'FE: resolve short absolute @aa:8 operands through a known base-register value.
  • --cycles: append Appendix A cycle estimates to assembly comments.
  • --callgraph-dot build\callgraph.dot: write a Graphviz DOT call graph.

Code Layout

  • h8536_decompiler.py: compatibility wrapper for the CLI.
  • h8536/cli.py: argument parsing and end-to-end orchestration.
  • h8536/decoder.py: instruction and effective-address decoding.
  • h8536/tables.py: manual-derived opcode/vector/register tables.
  • h8536/vectors.py: exception and DTC vector parsing.
  • h8536/analysis.py: recursive tracing, linear sweep, labels, function grouping, and call graph analysis.
  • h8536/data_analysis.py: unreached string and pointer-table candidate scans.
  • h8536/memory.py: manual-derived memory-region tagging.
  • h8536/cycles.py: Appendix A cycle estimate tables.
  • h8536/render.py: assembly and JSON output.
  • h8536/model.py, h8536/rom.py, h8536/formatting.py: shared data structures and helpers.
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