TASEmulators / TASEmulators/BizHawk
[NesHawk] Pass TakuikaNinja's FDS-Mirroring-Test
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- Dominant language
- C#
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Description
Summary
I recently helped discover some previously undocumented behaviour on the FDS. Bit 3 of $4030 reads return the value from bit 3 of $4025, which is the nametable arrangement/mirroring mode. I wrote a test program to verify the behaviour, and it fails on BizHawk's NesHawk core (and presumably SubNesHawk as well). Mesen2 and Nestopia have since implemented the behaviour.
NESdev forum post: https://forums.nesdev.org/viewtopic.php?p=300488#p300488
Test program source code: https://github.com/TakuikaNinja/FDS-Mirroring-Test
Repro
- Load the following test program: https://forums.nesdev.org/download/file.php?id=28216
- Test fails for
$4030.D3 R.
Host env.
- BizHawk 2.10; EndeavourOS on 6.13.8-zen1-1-zen
Screenshots
NesHawk:
Original hardware (Twin Famicom):
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by locating the NesHawk core's handling of FDS reads at $4030 and the mirroring value at $4025. Run the linked FDS-Mirroring-Test program and compare the $4030.D3 R result with the documented original-hardware behavior; done means the test passes in NesHawk.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- csharp
- Domain
- game-dev
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 45/100