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I have added comments to clarify the unknown behaviors that remain. 

Specifically, we don't know what happens when reading from 4016-4017 or 4218-421f, or when writing to 4016 or 4200, during the auto joypad polling sequence.
Presumably, nothing good.
This commit is contained in:
asuramaru 2020-10-23 23:38:08 -04:00 committed by Screwtapello
parent 42f9e68fb2
commit 6b38388a67
1 changed files with 5 additions and 0 deletions
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5
bsnes/sfc/cpu/io.cpp
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@ -12,11 +12,13 @@ auto CPU::readCPU(uint addr, uint8 data) -> uint8 {
case 0x2180: //WMDATA
return bus.read(0x7e0000 | io.wramAddress++, data);
//todo: it is not known what happens when reading from this register during auto-joypad polling
case 0x4016: //JOYSER0
data &= 0xfc;
data |= controllerPort1.device->data();
return data;
//todo: it is not known what happens when reading from this register during auto-joypad polling
case 0x4017: //JOYSER1
data &= 0xe0;
data |= 0x1c; //pins are connected to GND
@ -48,6 +50,7 @@ auto CPU::readCPU(uint addr, uint8 data) -> uint8 {
case 0x4216: return io.rdmpy >> 0; //RDMPYL
case 0x4217: return io.rdmpy >> 8; //RDMPYH
//todo: it is not known what happens when reading from these registers during auto-joypad polling
case 0x4218: return io.joy1 >> 0; //JOY1L
case 0x4219: return io.joy1 >> 8; //JOY1H
case 0x421a: return io.joy2 >> 0; //JOY2L
@ -122,6 +125,7 @@ auto CPU::writeCPU(uint addr, uint8 data) -> void {
io.wramAddress = io.wramAddress & 0x0ffff | (data & 1) << 16;
return;
//todo: it is not known what happens when writing to this register during auto-joypad polling
case 0x4016: //JOYSER0
//bit 0 is shared between JOYSER0 and JOYSER1:
//strobing $4016.d0 affects both controller port latches.
@ -130,6 +134,7 @@ auto CPU::writeCPU(uint addr, uint8 data) -> void {
controllerPort2.device->latch(data & 1);
return;
//todo: it is not known what happens when writing to this register during auto-joypad polling
case 0x4200: //NMITIMEN
io.autoJoypadPoll = data & 1;
nmitimenUpdate(data);