06719: coco12, coco3, other 6809?: SBCB instruction returns the wrong result

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
06719	Core	Minor	Always	Oct 18, 2017, 00:55	Oct 18, 2017, 22:25

Tester	star2root	View Status	Public	Platform	MAME (Self-compiled)
Assigned To	hap	Resolution	Fixed	OS
Status [?]	Resolved			Driver	trs/coco12.cpp
Version	0.187	Fixed in Version	0.191	Build
		Fixed in Git Commit		Github Pull Request #

Summary	06719: coco12, coco3, other 6809?: SBCB instruction returns the wrong result
Description	Run the following program and look at the number that appears on the line before the final OK prompt (on the 32x16 screen). 10 DATA5F,1C,00,1A,01,C2,FF 20 DATA34,01,35,02,B7,04,00,39 30 FORI=0TO14:READH$ 40 POKE&H3800+I,VAL("&H"+H$) 50 NEXT 60 CLS:PRINT 70 EXEC&H3800 80 PRINTPEEK(1024)AND15 On MAME 0.187, it's 7 while on the physical machine, it's 5. This value shows the N, Z, V and C flags that result from the SBCB instruction. The two values mean that MAME's SBCB set the V (overflow) flag to 1, while the physical machine set it to 0. I also tested on MAME 0.140, and it gave 5, interestingly. The assembly source is the following: org $3800 start clrb andcc #$00 ; clear all flags orcc #$01 ; set carry sbcb #$FF ; $00 - $ff - 1 = $00 pshs cc puls a sta $400 ; store resulting CC on 32x16 screen rts end start It can be assembled with LWTOOLS like this: lwasm -fdecb -o sbc.bin sbc.asm There is also a prepared a disk image with the Basic program on it: http://sarrazip.com/dev/sbc.dsk
Steps To Reproduce	Run the code in the description on the emulator.
Additional Information
Github Commit

Flags	Verified with Original
Regression Version	0.148u2
Affected Sets / Systems	coco12, coco3, other 6809?

Attached Files

No.14295 Tafoid Administrator Oct 18, 2017, 12:29	Updated regression version Appears related to 6809 core rewrite: https://github.com/mamedev/mame/commit/7c0baa1f6dd0ef221a89ec0f48ec91e0fe82668f
No.14300 richardcavell Tester Oct 18, 2017, 15:54	The issue is that the + here should be a - : https://github.com/mamedev/mame/blob/master/src/devices/cpu/m6809/base6x09.ops#L241 Credit goes to Pierre Sarrazin and Tim Lindner for investigating/finding this bug.