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Support save states on the DSP, SA-1, GSU, CX4, OBC1 and S-DD1 cores #307

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Support save states on the DSP, SA-1, GSU, CX4, OBC1 and S-DD1 cores #307

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28 changes: 27 additions & 1 deletion README.Savestates.FURiOUS.md
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Original file line number Diff line number Diff line change
Expand Up @@ -73,8 +73,34 @@ This file contains a few fixes for some games that has problems with APU. Exampl
64E9: 7E174B,2142;05C10D,A1 # This updates $7E174B with the latest $2142 state, it also patches 1 byte at the rom 0x05C10D (pc address)
```

### Special chips
Savestates originally only worked with games without a special chip, because the
firmware loads a different FPGA core for those and it had no in-game hook to run
custom code from. The coprocessor cores now carry that machinery, so savestates
also work on:

|Chip|Core|Notes|
---|---|---
|**DSP1-4** (uPD7725)|`fpga_dsp`|ST0010 (uPD96050) is not covered|
|**SA-1**|`fpga_sa1`|Mk.III only (does not fit the Mk.II FPGA)|
|**Super FX / GSU**|`fpga_gsu`||
|**CX4**|`fpga_cx4`||
|**OBC1**|`fpga_obc1`||
|**S-DD1**|`fpga_sdd1`||

SPC7110 and Super Game Boy are still not supported. As always, both the firmware
and the FPGA core files on the SD card have to be up to date — a stale
`fpga_<chip>` file makes the firmware fall back to a save without the chip state
instead of capturing garbage.

On the **Mk.II** the GSU and CX4 cores had no room left on the FPGA for both the
savestate machinery and the six hardware ROM-cheat comparators, so on those two
cores (Mk.II only) ROM cheats are applied by patching the loaded ROM image
instead. They work as before with one difference: the in-game cheat toggle no
longer switches ROM codes on and off — those follow the setting as it was when the
game was loaded. WRAM cheats are unaffected, and the Mk.III is unchanged.

### Known Savestates Issues
Savestates will only work with games that don't have special chips like SuperFX/SA-1/CX4, this is because the firmware loads another FPGA file for those games and it doesn't have necessary configuration to run custom code.

Flashcart savestates aren't perfect, the code runs on NMI to save a bunch of addresses to another place. You'll notice the song in some games will keep playing after you load state, others will just crash.

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2 changes: 1 addition & 1 deletion snes/Makefile
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@@ -1,5 +1,5 @@
IPS = header.ips
O65 = reset.o65 main.o65 font.o65 palette.o65 data.o65 const.o65 logo.o65 logospr.o65 dma.o65 filesel.o65 pad.o65 time.o65 sysinfo.o65 spc700.o65 spcplay.o65 menu.o65 menudata.o65 ui.o65 nmihook.o65 common.o65 savestate.o65 near.o65 # cheat.o65 # gfx.o65 # vars.o65
O65 = reset.o65 main.o65 font.o65 palette.o65 data.o65 const.o65 logo.o65 logospr.o65 dma.o65 filesel.o65 pad.o65 time.o65 sysinfo.o65 spc700.o65 spcplay.o65 menu.o65 menudata.o65 ui.o65 nmihook.o65 common.o65 savestate.o65 savestate_cx4.o65 near.o65 # cheat.o65 # gfx.o65 # vars.o65

OBJS = $(IPS) $(O65)
# stopgap measure to create both files as long as they are identical...
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