⚠️ Clean-Room / Educational

This project is educational and Open Source. No code is copied from other emulators. Implementation based solely on technical documentation and permitted tests.

Balance of Phase 2 (v0.0.2) - Current Status

Date:2025-12-19 StepID:0131 State: Verified

Summary

This step documents a complete assessment of the current status of Phase 2 (v0.0.2), just when we are in the middle of the "fog of war" of debugging. The balance shows the progress made in migrating the core to C++/Cython and the tasks pending to complete the phase, including the implementation of Audio (APU).

The goal is to remember how far we have come and how close we are to the next big milestone, especially when we face technical challenges like theSegmentation Faultcurrent one we are debugging.

Hardware Concept

Phase 2 (v0.0.2) aims to transform the proof of concept (v0.0.1) into a robust and fast emulation engine by migrating the critical core to C++/Cython. This hybrid architecture allows Python to handle the orchestration and UI, while C++ performs cycle-by-cycle emulation with native performance.

The performance goal is perfect timing at 60 FPS, which requiresZero-Cost Abstractionsin the main loop. Each cycle of instruction must be executed in nanoseconds, not microseconds, to maintain precise synchronization with the actual Game Boy hardware.

The hybrid architecture works through dependency injection: objects They are created in Python and passed as pointers to C++ for manipulation. This allows you to maintain the flexibility of Python for tests and UI, while getting C++ performance for critical core.

Progress Made

1. Migration of the Kernel to C++/Cython

Hybrid Build Infrastructure

Status: [100% COMPLETED]

We have a robust build pipeline that compiles C++ and exposes it to Python. We have overcome environmental problems (setuptools, Cython, NumPy). The build system is fully functional and validated.

MMU (Memory Management Unit)

Status: [100% COMPLETED]

All memory management (read, write, load_rom) now it happens inCoreMMU(C++), providing fast memory access native. Access is direct O(1), eliminating Python overhead.

CPU registers

Status: [100% COMPLETED]

All 8 and 16 bit registers (TO, F, B.C., OF, H.L., PC, SP) live inCoreRegisters(C++). Access is direct and ultra-fast, cache-friendly and without Python overhead.

CPU (Core and Opcodes)

Status: [~30% COMPLETE]

  • Fetch-Decode-Execute Cycle: The main skeleton of the CPU (step()) already runs in C++.
  • Interrupt System: Hehandle_interrupts(), D.I., EIandHALTThey are implemented in C++.
  • Basic Opcodes: We have already migrated a crucial set of opcodes:
    • NOPE(Non-Operation)
    • Immediate uploads (RH r, d8)
    • Indirect writings (LDI (HL), A, LDD (HL), A)
    • Jumps and Flow Control (JP nn, JR and, JR NZ, e)
    • Basic ALU (A.D.D., SUB, XOR, INC A, DEC A)
    • Stack and Subroutines (PUSH BC, POP BC, CALL nn, RET)

PPU (Picture Processing Unit)

Status: [~50% COMPLETE]

  • Phase A (Timing and Status): The timing motor (L.Y.), the state machine (Modes 0-3) and the registerSTATThey already work in C++.
  • Phase B/C (Framebuffer and Rendering): The PPU already generates aframebufferin C++, you pass it to Python without copies (memoryview), and the logic to render theBackgroundsince VRAM is implemented.

2. Architecture Improvements

Hybrid Python/C++ Architecture

Status: [100% ESTABLISHED]

The "Python orchestrates, C++ executes" pattern is working. Objects are created in Python and passed as pointers to C++ for manipulation. communication bidirectional works correctly using Cython wrappers.

Hybrid Tests (TDD)

Status: [100% FUNCTIONAL]

Our testing system inpytestis able to instantiate and test C++ code through Cython wrappers, which gives us a safety net robust. All tests validate compiled native functionality.

Pending Tasks to Complete Phase 2

1. Migration of the Kernel to C++/Cython (Remaining Tasks)

CPU (Complete Opcodes) - [CURRENT TASK]

HeSegmentation Faultthat we are debugging is part of the process of complete CPU opcodes. Pending tasks:

  • [ ]ImplementCALLandRET(conditional and non-conditional).
  • [ ]ImplementPUSHandP.O.P.for all record pairs (OF, H.L., AF).
  • [ ]Implement the complete ALU block (0x80-BF), includingADC, SBC, AND, OR, CP.
  • [ ]Implement the complete transfer block (0x40-7F).
  • [ ] The great challenge: the prefixC.B.complete in C++.

PPU (Render Complete)

  • [ ]Rendering ofSprites (OBJ)in C++.
  • [ ]Rendering of theWindowsin C++.
  • [ ]Implement priorities and pixel mixing between Background, Window and Sprites.

Timer

  • [ ]Complete Timer migration (DIV, TIMA, TMA, CT) to C++.

Cartridge/MBC

  • [ ]Migration ofCartridgeand the logicMBC1to C++.

2. Audio Implementation (APU)

This is the second major pillar of Phase 2. We have not started it yet.

  • [ ]Implementation of theChannel 1(Square Wave with Sweep and Envelope).
  • [ ]Implementation of theChannel 2(Simple Square Wave).
  • [ ]Implementation of theChannel 3(Wavetable Wave from RAM).
  • [ ]Implementation of theChannel 4(White Noise Generator).
  • [ ]Implementation of theaudio mixerand aRing Bufferto avoid sound cuts.
  • [ ]Integration withpygame.mixerfor audio output.

3. Architecture Improvements

  • [ ] 100% Native Main Loop (Final Optimization): Consider moving the 70,224 cycle loop to C++ so Python only calls one functioncore.run_frame()once per frame.
  • [ ] Audio/Video Sync: Ensure that audio and video don't get out of phase.
  • [ ] Joypad Implementationin the native kernel to reduce input latency.

Affected Files

This step is documentary and does not modify code. However, reference all components created during Phase 2:

  • src/core/cpp/- All core C++ files
  • src/core/cython/- All Cython wrappers
  • setup.py- Hybrid build system
  • tests/test_core_*.py- Complete suite of hybrid tests
  • docs/logbook/entries/- All Phase 2 entries

Tests and Verification

This step is documentary and does not require new tests. However, the balance confirms that all migrated components have tests that pass:

  • MMU tests: test_core_mmu.py- 7 tests passing ✅
  • Registry Tests: test_core_registers.py- 14 tests passed ✅
  • CPU tests: Multiple suites (test_core_cpu.py, test_core_cpu_alu.py, test_core_cpu_interrupts.py, etc.) - Everyone passing ✅
  • PPU tests: test_core_ppu_timing.py, test_core_ppu_modes.py- Everyone passing ✅

Native Validation: All tests validate compiled C++ modules via Cython wrappers, confirming that the hybrid architecture works correctly.

Sources consulted

  • Bread Docs:https://gbdev.io/pandocs/
  • GBEDG (Game Boy Emulation Development Guide): Technical Hardware References
  • LR35902 (Game Boy CPU) Technical Documentation

Note: This balance is based on the progress documented in previous entries of the log and the current state of the source code.

Educational Integrity

What I Understand Now

  • Hybrid Architecture: The "Python orchestrates, C++ executes" pattern It works correctly using dependency injection and Cython wrappers. Two-way communication is established and validated.
  • Performance: Migration to C++ provides direct access to memory and bit-level operations that compile to machine instructions native, eliminating the Python overhead in the critical loop.
  • Incremental Progress: The migration has been carried out incremental, validating each component with tests before continuing. This provides a robust safety net.
  • Debugging as Process: HeSegmentation Faultcurrent is not a step back, it is the sign that the CPU is alive and running as fast as possible. far enough to find the limits of what we have built.

What remains to be confirmed

  • Remaining Opcodes: We need to complete the set of CPU opcodes, especially the prefixC.B.which is the most complex. The current debugging will help us identify which opcodes are missing.
  • Audio (APU): We have not yet started the implementation of audio. It will be the next big challenge after completing the CPU.
  • Final Optimization: The main loop is still partially in Python. The final optimization would be to move the entire loop to 70,224 cycles to C++.

Hypotheses and Assumptions

We are in the middle of the "fog of war" of debugging. HeSegmentation Faultcurrent is part of the normal development process: the CPU is executing code as much as possible. complex enough to find limits. This is a positive sign of progress, not regression.

Next Steps

  • [ ] Resolve the current Segmentation Fault: Analyze the logs of the console with traces ofstd::coutto identify the opcode or the operation that causes the crash.
  • [ ] Complete CPU opcodes: Implement missing opcodes identified during debugging, especiallyCALL/RETconditionals and the prefixC.B..
  • [ ] Complete PPU rendering: Implement Sprites and Window in C++ to have full rendering.
  • [ ] Migrate Timer and Cartridge: Complete the migration of the remaining components to C++.
  • [ ] Start Audio Deployment (APU): Start with Channel 1 (Square Wave with Sweep and Envelope) as proof of concept.