feat(zaparoo): coordinate frontend scanout and Core recovery by wizzomafizzo · Pull Request #24 · ZaparooProject/Main_MiSTer

wizzomafizzo · 2026-09-05T12:31:16Z

Summary

Coordinate frontend scanout through an acknowledged inherited socket lease. Main abstains from FPGA writes while the child owns the bus; optionally load only the qualified 6.18.38-MiSTer module, with no force-load or unload.
Keep HDMI startup/handoff black during video probing, preserve restart continuity, and retain bounded fb0 fallback. Native CRT and Direct Video keep their existing paths.
Preserve ownership when a child stop times out: abort core loads, re-exec, restarts and script-console takeovers rather than competing with an unreaped writer.
Recover stale Core PID-file cases while frontend is active, with throttled service-ensure attempts. The detached helper restores its saved startup affinity and closes inherited Main device descriptors. Missing PID files are ignored; this is a liveness heuristic, not diagnosis of a specific crash cause.
Retain the original temp-MGL fix: /media/fat/.LASTLAUNCH.mgl does not overwrite Core's real /tmp/ACTIVEGAME path. Other launch tracking stays unchanged.

Ref ZaparooProject/Menu_MiSTer#4. Ref ZaparooProject/zaparoo-core#1432.

Verification

Current master and official upstream are ancestors of this branch; master merged without conflicts.
Full GNU ARM 10.2.1 rebuild (make -B -j4), no compiler warnings; output verified as ARM EABI5. Final merged tree build and whitespace checks pass.
Compile-time bootstrap checks cover startup bounds, fallback grace, live-lease timeout exclusion and timer wraparound.
Reviewed stop-failure propagation through core load, re-exec, restart and both script-entry paths. Main-only support additions and surgical upstream hooks; no Makefile or CI changes.
Earlier temp-MGL and paired scanout/black-handoff candidates were device-tested. Latest stop-timeout and watchdog-helper fixes have not been deployed or fault-injected on hardware. This repo has no PR build workflow; release workflows were not dispatched.

Scope and limitations

Targets master only, not stable. No device changes, stable promotion or release performed. Requires matching Menu/frontend integration; module packaging and broader CRT/lifecycle acceptance remain separate. Independent raw-memory renderers are unsupported. Menu module licensing risk was explicitly accepted by the owner; no license changes or legal-clearance claim.

Summary by CodeRabbit

New Features
- Added optional frontend scanout support for compatible HDMI setups, including coordinated video ownership and black-screen startup handoff.
- Added automatic recovery when the Zaparoo Core service stops unexpectedly.
- Expanded alternate-launcher support for menu-based launches and framebuffer control.
Bug Fixes
- Prevented conflicting FPGA and framebuffer access during launcher handoffs.
- Improved handling when launcher shutdown or script preparation cannot complete safely.
- Avoided recording temporary launcher paths as the active game.
Documentation
- Updated architecture and scanout behavior documentation.

… MGL zaparoo_active_game_set_core() runs on every user_io_init(), including the app_restart() re-exec after a load_core, and wrote the MGL path for any .mgl start. Zaparoo Core and mrext send load_core with /media/fat/.LASTLAUNCH.mgl after writing the real game path themselves, so /tmp/ACTIVEGAME flipped from the game to the MGL about a second after every launch. Nothing wrote the game back: menu.cpp skips recent_update() while an MGL is processing. Skip the write for that one path. It is rewritten on every launch, so it never identifies a game. Bare-core starts still clear, menu-selected MRA and MGL starts still write, and set_file is unchanged.

coderabbitai · 2026-09-05T12:32:10Z

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📝 Walkthrough

Walkthrough

The change adds HDMI scanout lease coordination, bounded black-screen bootstrap handling, FPGA and video ownership guards, Core liveness recovery, service-start cleanup, and temporary MGL active-game tracking behavior.

Changes

Launcher scanout ownership

Layer / File(s)	Summary
Scanout protocol and bootstrap state `support/zaparoo/scanout.*`, `support/zaparoo/bootstrap.h`, `support/zaparoo/SCANOUT.md`	The new scanout module negotiates eligible HDMI ownership through an inherited socket, checks mapping conflicts, loads the optional module, and manages lease state. Bootstrap state provides bounded hidden, fallback, grant, cancel, and expiry transitions.
Launcher lifecycle integration `support/zaparoo/alt_launcher.*`	The launcher prepares scanout before child startup, passes the child environment, tracks ownership, preserves black output during handoffs, and stops or falls back when child termination times out.
Video and FPGA ownership guards `fpga_io.cpp`, `video.cpp`, `menu.cpp`	FPGA and framebuffer writes stop while the launcher owns UIO or hides the framebuffer. Shutdown and script preparation failures now block video takeover and script execution.

Core recovery and tracking

Layer / File(s)	Summary
Core watchdog and service restart `support/zaparoo/core_watchdog.`, `support/zaparoo/save.cpp`, `support/zaparoo/service_boot.`, `ZAPAROO_FORK.md`	The poll loop detects stale Core PIDs and starts an idempotent service helper. The helper restores saved CPU affinity, closes inherited descriptors, and retries interrupted waits.
Active-game and menu launch handling `support/zaparoo/active_game.cpp`, `user_io.cpp`, `menu.cpp`	The tracker ignores `/media/fat/.LASTLAUNCH.mgl`. Native menu cores with an RBF path now start the alternate launcher, and script handoff stops when launcher termination fails.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~60 minutes

Merge Risk: 🟡 Moderate · up to cfe73

A reused PID can leave Core stopped without recovery while the frontend remains active, so process identity validation should be added before merge.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 16.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 74 functions across 15 files. (2 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes the primary changes: frontend scanout coordination and Core recovery.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 16.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 74 functions across 15 files. (2 skipped: 2 unsupported.)

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Reuse the detached service ensure, preserve startup affinity and close inherited hardware descriptors on watchdog restarts. Ignore missing PID files and throttle retries.

Grant FPGA ownership only after video setup and an acknowledged child request. Keep live-writer ownership through stop timeouts, and abort unsafe core/script takeovers. Preserve fb0 fallback and exclude native CRT/Direct Video.

coderabbitai

Actionable comments posted: 1

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Inline comments:
In `@support/zaparoo/core_watchdog.cpp`:
- Line 68: Update the watchdog’s liveness check around kill(pid, 0) to validate
that the PID still belongs to the originally launched Core process using a
stored start-time or other stable identity read from /proc. Only clear
s_restart_timer when both the PID is live and its identity matches; otherwise
preserve the restart path.

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📥 Commits

Reviewing files that changed from the base of the PR and between 9f2abdf and cfe734c.

📒 Files selected for processing (16)

ZAPAROO_FORK.md
fpga_io.cpp
menu.cpp
support/zaparoo/SCANOUT.md
support/zaparoo/alt_launcher.cpp
support/zaparoo/alt_launcher.h
support/zaparoo/bootstrap.h
support/zaparoo/core_watchdog.cpp
support/zaparoo/core_watchdog.h
support/zaparoo/save.cpp
support/zaparoo/scanout.cpp
support/zaparoo/scanout.h
support/zaparoo/service_boot.cpp
support/zaparoo/service_boot.h
user_io.cpp
video.cpp

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wizzomafizzo mentioned this pull request Sep 5, 2026

fix(mister): identify MGL-observed games by the file they load ZaparooProject/zaparoo-core#1432

Merged

wizzomafizzo added 3 commits September 9, 2026 14:32

feat(zaparoo): recover stale Core services while frontend is active

2c6c36d

Reuse the detached service ensure, preserve startup affinity and close inherited hardware descriptors on watchdog restarts. Ignore missing PID files and throttle retries.

merge: sync frontend integration with current master

cfe734c

wizzomafizzo changed the title ~~fix(zaparoo): leave ACTIVEGAME alone when started from Zaparoo's temp MGL~~ feat(zaparoo): coordinate frontend scanout and Core recovery Sep 9, 2026

coderabbitai Bot reviewed Sep 9, 2026

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Comment thread support/zaparoo/core_watchdog.cpp Outdated

fix(zaparoo): verify Core identity in watchdog

04bf080

wizzomafizzo mentioned this pull request Sep 9, 2026

fix(daemon): recover stale service PID files safely ZaparooProject/zaparoo-core#1469

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feat(zaparoo): coordinate frontend scanout and Core recovery - #24

feat(zaparoo): coordinate frontend scanout and Core recovery#24
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fix/zaparoo-active-game-temp-mgl

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