07892: sxeviousj: Inserting coin automatically start 2 player game with issues

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
07892	Gameplay	Minor	Always	Mar 1, 2021, 08:48	Mar 1, 2021, 11:16

Tester	Augusto	View Status	Public	Platform	SDLMAME
Assigned To		Resolution	Open	OS	Linux (64-bit)
Status [?]	Confirmed			Driver	galaga.cpp
Version	0.229	Fixed in Version		Build	64-bit
		Fixed in Git Commit		Github Pull Request #

Summary	07892: sxeviousj: Inserting coin automatically start 2 player game with issues
Description	Insert one coin. Automatically start 2 player game not using the inserted credit. Solvalou goes totally to left without player input. When that gameplay end is possible start an new gameplay with correct control input. To play need insert one coin wait to both 2 player game end or insert coin and after reset. Only affect sxeviousj.
Steps To Reproduce
Additional Information
Github Commit

Flags
Regression Version	0.221
Affected Sets / Systems	sxeviousj

Attached Files

No.18502 Tafoid Administrator Mar 1, 2021, 11:16 edited on: Mar 1, 2021, 11:17	In particular, work done on April 25, 2020 seems to be the culprit. Namco custom chip improvements https://github.com/mamedev/mame/commit/3a6317b0f47a1596777537b7c7544818076f9397 Given the fact that it 'clears up' after the failed start tends to suggest a race condition as mentioned in the source text of one of the custom control chips. Note that Xevious has a potential race condition at 0xE9. It checks if the control register is 0x10 (chip disabled), then 4 instructions later acts on that check. If an NMI occurs between, it can crash. Why it only affects SXEVIOUSJ, it is unknown. All other tested xevious/clone sets do not exhibit this under testing.

No.18502

Tafoid

Administrator

Mar 1, 2021, 11:16

edited on: Mar 1, 2021, 11:17

In particular, work done on April 25, 2020 seems to be the culprit.
Namco custom chip improvements
https://github.com/mamedev/mame/commit/3a6317b0f47a1596777537b7c7544818076f9397

Given the fact that it 'clears up' after the failed start tends to suggest a race condition as mentioned in the source text of one of the custom control chips.

    Note that Xevious has a potential race condition at 0xE9. It checks if
    the control register is 0x10 (chip disabled), then 4 instructions later
    acts on that check. If an NMI occurs between, it can crash.

Why it only affects SXEVIOUSJ, it is unknown. All other tested xevious/clone sets do not exhibit this under testing.