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TRB and TSB 65c02 instructions don't set Z bit correctly #32

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KrisKennaway opened this issue May 8, 2017 · 2 comments
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TRB and TSB 65c02 instructions don't set Z bit correctly #32

KrisKennaway opened this issue May 8, 2017 · 2 comments

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@KrisKennaway
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I think the logic for setting the zero bit for TRB and TSB is inverted. It should be setting Z if "m & self.a == 0" (not != 0)

This matches what is described here: http://6502.org/tutorials/65c02opcodes.html#4 and I can replicate this behaviour in another emulator. For example, here's what I get on the Virtual II emulator configured to emulate a 65C02:

*0800: a9 e0 85 bb a9 70 14 bb 00
*0800L
0800- A9 E0 LDA #$E0
0802- 85 BB STA $BB
0804- A9 70 LDA #$70
0806- 14 ???
0807- BB ??? # TRB $BB
0808- 00 BRK
*0800g
080A- A=70 X=FF Y=FF P=30 S=EA

P = 0x30 has the ZERO bit (0x2) clear but test_trb_sp_ones expects it (and mpu65c02 sets it). Similarly for all the other TRB and TSB test cases.

I found this when adapting these conformance test suites to validate another 65c02 simulator which turned out not to have this bug (but it did find many others -- so these tests were super useful, although now perhaps I have to look again more carefully!)
KrisKennaway added a commit to KrisKennaway/py6502 that referenced this issue May 8, 2017
@KrisKennaway
Add a 65C02 conformance test suite from the py65 project (some tests
6d2074a 
commented out because they are for alternate versions of the 65C02 and
we do not implement these opcodes)

Fix some arithmetic underflow bugs due to python's % operator working
differently than assumed on negative numbers (they aren't brought into
the [0...n) interval)

65C02 actually fixed some of the processor bugs we implemented in a
previous CL:
- indirect JMP no longer mis-reads the high byte when crossing page
  boundaries
- DECIMAL flag now correctly reset across BRK

So unimplement these processor bugs.

Interestingly, the py65 project where I got these tests from seems to
have bugs in handling of the Z bit in the TSB/TRB operations
(see mnaberez/py65#32), and this
implementation seems to do it correctly.

Unfortunately this implementation also had a buggy TSB
(result = operand | self.a, not '+')

DEA and INA update A
@BigEd
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BigEd commented May 9, 2017

Thanks for the report @KrisKennaway - I came to have a look and see that @mnaberez has already fixed it. Thanks Mike!

@KrisKennaway I do recommend also running Klaus Dormann's test suite if you can. He has an extended suite for the 'C02. See
https://github.com/Klaus2m5/6502_65C02_functional_tests

@KrisKennaway
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Thanks for the quick response, and for the pointer to Klaus's test suites. I have got that running and it looks like the 65C02 one is not passing still (the 6502 and decimal tests both are), I'll take a closer look and open a new issue.

@KrisKennaway KrisKennaway mentioned this issue May 11, 2017
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@BigEd @KrisKennaway