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fix(dma): implement obscure behaviour for DMAs from ROM

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-11-20 17:42:46 -04:00
parent f31699d921
commit 4ed4f8e143
1 changed files with 10 additions and 5 deletions
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15
src/core/bus/dma.zig
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@ -256,11 +256,16 @@ fn DmaController(comptime id: u2) type {
cpu.bus.write(u16, dad_addr, @truncate(u16, rotr(u32, self.data_latch, 8 * (dad_addr & 3))));
}
switch (sad_adj) {
.Increment => self.sad_latch +%= offset,
.Decrement => self.sad_latch -%= offset,
.IncrementReload => log.err("{} is a prohibited adjustment on SAD", .{sad_adj}),
.Fixed => {},
switch (@truncate(u8, sad_addr >> 24)) {
// according to fleroviux, DMAs with a source address in ROM misbehave
// the resultant behaviour is that the source address will increment despite what DMAXCNT says
0x08...0x0D => self.sad_latch +%= offset, // obscure behaviour
else => switch (sad_adj) {
.Increment => self.sad_latch +%= offset,
.Decrement => self.sad_latch -%= offset,
.IncrementReload => log.err("{} is a prohibited adjustment on SAD", .{sad_adj}),
.Fixed => {},
},
}
switch (dad_adj) {