One of the issues that were opened involved incorrect operation of some instructions in very specific cases, the CPU LandMark System Speed 6.0 test:
https://github.com/MiSTer-devel/PCXT_MiSTer/issues/26
Well, after several days of debugging, and with the help of @MicroCoreLabs, I have managed to get it working:
- LM60.png (226.64 KiB) Viewed 1104 times
The problem was due to the fact that in certain scenarios, the CMP instruction did not set the overflow flag correctly. Actually, it was related to the SUB instruction.
MicroCoreLabs had already detected this problem with the ADC/SBB instructions... and had a solution for it:
https://github.com/MiSTer-devel/PCXT_Mi ... e8437fe186
to which I have added the ADD/SUB solution:
https://github.com/MiSTer-devel/PCXT_Mi ... 5c7302f7c1
I attach a corresponding binary for testing purposes, before sending a general update to everyone.
It may also be that this fix will solve other problems. Any feedback is welcome.