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Add description of swtrilgy patch from MAME

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Star Wars Trilogy will sometimes write to a JTAG register and then read it back to verify it, but this doesn't work correctly with Supermodel's current JTAG implementation; it will try again and never succeed, getting stuck in an infinite loop. This patch stops the code from branching up and trying the write/read cycle again, allowing the subroutine to continue normally.

We need to implement shift register widths correctly for each JTAG device (Mercury, Venus, Earth, etc.) for the unpatched code to work properly... right now Supermodel implements one JTAG device with a huge 197-bit data shift register
This commit is contained in:
Matthew Daniels 2023-05-16 02:49:35 +01:00 committed by trzy
parent ac0e6407b4
commit 84aa972ef2
1 changed files with 4 additions and 7 deletions
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9
Config/Games.xml
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@ -2273,8 +2273,8 @@
<roms>
<patches>
<!--
The purpose of this patch from MAME is no longer clear. Force feedback
or JTAG related? If anyone knows, please update this note.
Patch from MAME: forces JTAG write/read tests to succeed, otherwise
the game spins in a loop forever (until we implement JTAG properly)
-->
<patch region="crom" bits="32" offset="0xf6e44" value="0x60000000" />
</patches>
@ -2362,10 +2362,7 @@
</hardware>
<roms>
<patches>
<!--
The purpose of this patch from MAME is no longer clear. Force feedback
or JTAG related? If anyone knows, please update this note.
-->
<!-- Patch from MAME, see swtrilgy for details -->
<patch region="crom" bits="32" offset="0xf6dd0" value="0x60000000" />
</patches>
<region name="crom" stride="8" chunk_size="2" byte_swap="true">