SA-1 DMA won't transfer to bank 0x41 #309
Comments
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Do you happen to have a test case? |
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Ultimately, finding this came from some custom code for handling dynamic sprites used in Vitor's SA-1 enhancement patch for SMW. You can see an example of the code used here, among a few other spots; Is that sufficient, or were you looking more for a test ROM of some sort? |
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A test ROM would always be helpful. The only reference I see to anything 18-bit in the manual is related to the Timer Circuit, in Book 2, Page 1-2-2. On the other hand I do see that DDA is a 24-bit register on Page 1-4-22. So I believe using a |
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Sorry, the 18 bit size I was getting was from table 1-9-2 on page 1-9-3. Presumably it says 18 bits because that's the maximum possible size of BW-RAM, even if DDA is 24 bits. |
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SA-1 DMA should work for banks $40-$43, it's documented on SA-1 dev book. I
recommend changing the register to 24-bit.
I don't have a test ROM available right now but I can test this in the
nearby future.
Vitor
Em dom., 14 de jan. de 2024, 00:36, Fernap ***@***.***>
escreveu:
… Sorry, the 18 bit size I was getting was from table 1-9-2 on page 1-9-3.
Presumably it says 18 bits because that's the maximum possible size of
BW-RAM, even if DDA is 24 bits.
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DDA was incorrectly capped at 16 bits instead of 24, making DMAs to BWRAM banks 0x41-43 be sent to the corresponding spot in 0x40 instead. See [the corresponding bug in bsnes](bsnes-emu/bsnes#309) for some more context.
Any attempts to use SA-1 side DMA to BWRAM with a destination in bank 0x41 will result in a transfer to the corresponding address at bank 0x40 instead. Changing line 6 in bsnes/sfc/coprocessor/sa1/dma.cpp from a
uint16to auint24should fix the problem (the SNES dev manual indicates 18 bits are actually used). This bug was apparently introduced here.Credit to @VitorVilela7 and @TheLX5 for originally diagnosing the problem, and Vitor for tracking down when the regression was introduced.
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