Add comprehensive frame pacing support #71
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Adds Bresenham-style frame pacing to decouple emulation from display refresh rate. Handles any mismatch: 60fps on 72Hz (M17), 50fps PAL games on 60Hz displays, etc. Core algorithm (frame_pacer.c): - Q16.16 fixed-point accumulator (no float drift) - Direct mode bypass for mismatches ≤2% (handled by audio rate control) - 2% tolerance based on RetroArch rate control research (Arntzen 2012) Platform API additions: - PLAT_getDisplayHz() - returns panel refresh rate - PLAT_measureVsyncInterval() - for future adaptive measurement - PLAT_clearBlit() - switches from game to UI rendering mode Also refactors M17 platform.c to use shared render_sdl2 backend.
Dual-mode audio/video synchronization with compile-time selection:
Vsync mode (default):
- Frame pacing via Bresenham accumulator
- Dual-timescale PI audio rate control
- Non-blocking audio writes
Audioclock mode (M17):
- Audio hardware clock drives timing
- Blocking audio writes (up to 10ms when buffer full)
- No frame pacing or rate control needed
Changes:
- Add minarch_loop_{vsync,audioclock}.inc with mode-specific main loops
- Dual SND_batchSamples() implementation in api.c
- Increase SND_CHUNK_SAMPLES 256→512 (benefits all platforms)
- Enable audioclock mode for M17 via -DSYNC_MODE_AUDIOCLOCK
Fixes audio stuttering on M17 where unstable vsync caused underruns.
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Pull request overview
This PR adds comprehensive frame pacing support to decouple emulation timing from display refresh rates, enabling smooth gameplay on devices with non-60Hz displays (e.g., M17's 73Hz panel). It introduces two sync modes: vsync-driven with Bresenham-style frame pacing (default) and audio-driven timing (for unstable vsync devices like M17).
Key changes:
- New frame pacing system using Q16.16 fixed-point arithmetic to avoid floating-point drift
- Two compilation modes: vsync-driven (default) with frame repeats for non-matching Hz, and audioclock mode (SYNC_MODE_AUDIOCLOCK) with audio hardware timing
- M17 platform refactored to use shared render_sdl2 backend and configured for audioclock mode due to unstable vsync
Reviewed changes
Copilot reviewed 32 out of 32 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
| workspace/all/minarch/frame_pacer.h | Frame pacer API with Q16.16 fixed-point Bresenham algorithm |
| workspace/all/minarch/frame_pacer.c | Frame pacer implementation with direct mode bypass and accumulator logic |
| workspace/all/minarch/minarch_loop_vsync.inc | Vsync-driven main loop with frame pacing (default mode) |
| workspace/all/minarch/minarch_loop_audioclock.inc | Audio-driven main loop with blocking writes (SYNC_MODE_AUDIOCLOCK) |
| workspace/all/minarch/minarch.c | Updated to use conditional compilation for sync modes, added frame pacer state |
| workspace/all/minarch/minarch_cpu.c | Added scaling_disabled flag to skip CPU scaling on single-frequency devices |
| workspace/all/minarch/minarch_cpu.h | Added scaling_disabled field to CPU state |
| workspace/all/common/api.c | Added audioclock mode with blocking audio writes and fixed 1.0 resampling ratio |
| workspace/all/common/api.h | Added PLAT_getDisplayHz and PLAT_measureVsyncInterval API declarations |
| workspace/all/common/defines.h | Increased audio chunk size from 256 to 512 samples for more stable timing |
| workspace/all/common/render_sdl2.c | Added clearBlit, getDisplayHz, and measureVsyncInterval implementations |
| workspace/all/common/render_sdl2.h | Added function declarations for new SDL2 rendering functions |
| workspace/m17/platform/platform.c | Refactored to use render_sdl2 backend, returns 73.0 Hz for display rate |
| workspace/m17/platform/platform.h | Corrected display specs (273→272 height, 7.0→4.3 diagonal) |
| workspace/m17/platform/makefile.env | Added SYNC_MODE_AUDIOCLOCK flag for unstable vsync |
| workspace/m17/README.md | Updated hardware specs and added exFAT filesystem requirement |
| workspace/desktop/platform/platform.c | Added clearBlit, getDisplayHz (60.0), and measureVsyncInterval (returns 0) |
| workspace/zero28/platform/platform.c | Added clearBlit, getDisplayHz, and measureVsyncInterval using SDL2 backend |
| workspace/tg5040/platform/platform.c | Added clearBlit, getDisplayHz, and measureVsyncInterval using SDL2 backend |
| workspace/rgb30/platform/platform.c | Added clearBlit, getDisplayHz, and measureVsyncInterval using SDL2 backend |
| workspace/rg35xxplus/platform/platform.c | Added clearBlit, getDisplayHz, and measureVsyncInterval using SDL2 backend |
| workspace/rg35xx/platform/platform.c | Added clearBlit, returns 60.0 Hz, implements ioctl-based vsync measurement |
| workspace/my355/platform/platform.c | Added clearBlit, getDisplayHz, and measureVsyncInterval using SDL2 backend |
| workspace/my282/platform/platform.c | Added clearBlit, getDisplayHz, and measureVsyncInterval using SDL2 backend |
| workspace/miyoomini/platform/platform.c | Added clearBlit, returns 60.0 Hz, implements SDL_Flip-based vsync measurement |
| workspace/magicmini/platform/platform.c | Added clearBlit, getDisplayHz, and measureVsyncInterval using SDL2 backend |
| workspace/trimuismart/platform/platform.c | Added clearBlit, returns 60.0 Hz, implements ioctl-based vsync measurement |
| tests/unit/all/common/test_frame_pacer.c | Comprehensive unit tests for frame pacing algorithm (385 lines, 24 tests) |
| tests/unit/all/common/test_minarch_cpu.c | Added tests for scaling_disabled scenarios |
| workspace/all/minarch/makefile | Added frame_pacer.c to build |
| makefile.qa | Added frame_pacer_test to test executables |
| skeleton/BASE/README.md | Added exFAT filesystem requirement for M17 |
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Fixed #70.