Revision 1 CPU DMA crash

Little is known about why the CPU revision 1 DMA crash happens. In 2015, Ramsis wrote a test rom to trigger it. ^[2]

Trigger

• kicking of an HDMA at about the same time that a General Purpose DMA finishes

Symptoms

• Sometimes the 5A22 will crash
• Sometimes the HDMA will not happen correctly

Workarounds

• Use GPDMA only during vblank
• Make sure HDMA starts in the middle of a GPDMA data transfer
• Avoid HDMA
• Adjust the time at which GPDMA begins
• Decrease the number of bytes transferred during GPDMA

See Also

• Revision 1 PPU1 Time Over Bug

References

1. page 2-25-1 of Book I of the official Super Nintendo development manual
2. https://forums.nesdev.org/viewtopic.php?t=13280