Radical Optimization: Cleaning Logs and Controls

Summary

Classic Tetris worked correctly but at only 14 FPS due to debug log saturation which were executed thousands of times per second. All interruption logs were completely removed, heartbeat and OAM SAMPLE that were running in a loop. Additionally, keyboard mapping was improved by adding alternatives (K_a and K_s) for greater convenience. The implementation of LYC in the PPU has been verified and is correct. The result: the emulator now reaches 60 FPS and Tetris is fully playable.

Hardware Concept

In an emulator, performance is critical. Each operation is executed millions of times per second (like logging) can become a bottleneck. The Game Boy runs approximately 4.19 million cycles per second, and every interrupt, every PPU mode change, and every transfer DMA generates events that, if logged, flood the console and slow down the emulator.

Logging must be selective: only activate in debug mode or for specific diagnosis. In production (normal execution), the emulator should be silent except for critical errors.

Keyboard controls should be intuitive and offer multiple options for convenience. The original Game Boy had 8 buttons (4-way + A + B + Start + Select), and the mapping must reflect this naturally.

Implementation

Three main sources of logs running in a loop were identified:

1. Interrupt logsinsrc/cpu/core.py: They were fired every time an interrupt (V-Blank, STAT, Timer, etc.) was processed, which occurs hundreds of times per second.
2. Heartbeat and OAM SAMPLEinsrc/viboy.py: They were executed every 300 frames (heartbeat) and every second (OAM SAMPLE), generating constant logs.
3. Diagnostic logswere already discussed in previous steps, but it was verified that there would be none active.

Modified components

• src/cpu/core.py: Commented the interruption log (line 506)
• src/viboy.py: Commented heartbeat and OAM SAMPLE logs (lines 455-476)
• src/viboy.py: Improved keyboard mapping by adding K_a and K_s alternatives

Design decisions

It was decided to comment out the logs instead of deleting them completely, to facilitate future debugging. The logs are clearly marked with explanatory comments indicating that they are disabled for performance and should only be activated if necessary for diagnosis.

Keyboard mapping was improved by adding alternatives (K_a and K_s) in addition to the original keys (K_z and K_x), allowing users to use the settings that are most comfortable for them.

Affected Files

• src/cpu/core.py- Commented interruption log to improve performance
• src/viboy.py- Commented heartbeat and OAM SAMPLE logs, improved keyboard mapping

Tests and Verification

Manual verification with Classic Tetris:

• ROM:Tetris (user-contributed ROM, not distributed)
• Execution mode:UI with pygame, logging disabled
• Success Criterion:The emulator must reach 60 FPS and be fully playable
• Observation:
  • Before: 14 FPS with logs saturating the console
  • After: 60 stable FPS, no logs on console, completely playable
  • Controls work correctly (ENTER for Start, Z/A for A, X/S for B, arrows for directions)
• Result: Verified- The emulator works perfectly at 60 FPS

LYC implementation verification:

• Reviewed the implementation of LYC insrc/gpu/ppu.py
• The logic is correct: check if LY == LYC, update bit 2 of STAT, and request interrupt if STAT bit 6 is active
• The implementation is complete and functional

Sources consulted

• Bread Docs:https://gbdev.io/pandocs/- General hardware reference
• Implementation based on general knowledge of LR35902 architecture and performance optimization

Educational Integrity

Next Steps

• [ ] Check if the LYC fix allows Pokémon Red to pass the logo (if not, investigate other causes)
• [ ] Continue to improve compatibility with other games
• [ ] Implement additional features as needed