implementation of SA-1 BW-RAM protection

Manually cherry-picked ares commit ares-emulator/ares@70f3610. Co-Authored-By: absindx <59403574+absindx@users.noreply.github.com>
bsnes-emu · Mar 1, 2024 · 196a41c · 196a41c
1 parent 4faca65
commit 196a41c
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Showing 3 changed files with 22 additions and 3 deletions.
diff --git a/bsnes/sfc/coprocessor/sa1/bwram.cpp b/bsnes/sfc/coprocessor/sa1/bwram.cpp
@@ -39,6 +39,8 @@ auto SA1::BWRAM::writeCPU(uint address, uint8 data) -> void {
  address = sa1.mmio.sbm * 0x2000 + (address & 0x1fff);
  }
 
+ //note: BW-RAM protection works only when both SWEN and CWEN are disabled.
+ if(!sa1.mmio.swen && !sa1.mmio.cwen && (address & 0x3ffff) < 0x100 << sa1.mmio.bwp) return;
  return write(address, data);
 }
 
@@ -71,6 +73,15 @@ auto SA1::BWRAM::readLinear(uint address, uint8 data) -> uint8 {
 }
 
 auto SA1::BWRAM::writeLinear(uint address, uint8 data) -> void {
+ //note: BW-RAM protection works only when both SWEN and CWEN are disabled.
+ //this is required for Kirby's Dream Land 3 to work:
+ //* BWPA = 02 (protect 400000-4003ff)
+ //* SWEN = 80 (writes enabled)
+ //* CWEN = 00 (writes disabled)
+ //KDL3 proceeds to write to 4001ax and 40032x which must succeed.
+ //note: BWPA also affects SA-1 protection
+ if(!sa1.mmio.swen && !sa1.mmio.cwen && (address & 0x3ffff) < 0x100 << sa1.mmio.bwp) return;
+
  return write(address, data);
 }
 

diff --git a/bsnes/sfc/coprocessor/sa1/io.cpp b/bsnes/sfc/coprocessor/sa1/io.cpp
@@ -108,8 +108,16 @@ auto SA1::writeIOCPU(uint address, uint8 data) -> void {
  //(CCNT) SA-1 control
  case 0x2200: {
  if(mmio.sa1_resb && !(data & 0x20)) {
- //reset SA-1 CPU (PC bank set to 0x00)
+ //reset SA-1 CPU (PC bank and data bank set to 0x00, clear STP status)
  r.pc.d = mmio.crv;
+ r.b = 0x00;
+ r.stp = false;
+ //todo: probably needs a SA-1 CPU reset
+ //reset r.s, r.e, r.wai ...
+
+ //reset io status
+ //todo: reset timing is unknown, CIWP is set to 0 at reset
+ mmio.ciwp = 0x00;
  }
 
  mmio.sa1_irq = (data & 0x80);

diff --git a/bsnes/sfc/coprocessor/sa1/memory.cpp b/bsnes/sfc/coprocessor/sa1/memory.cpp
@@ -37,7 +37,7 @@ auto SA1::read(uint address) -> uint8 {
  }
 
  if((address & 0x40e000) == 0x006000 //00-3f,80-bf:6000-7fff
- || (address & 0xf00000) == 0x400000 //40-4f:0000-ffff
+ || (address & 0xe00000) == 0x400000 //40-5f:0000-ffff
  || (address & 0xf00000) == 0x600000 //60-6f:0000-ffff
  ) {
  step();
@@ -81,7 +81,7 @@ auto SA1::write(uint address, uint8 data) -> void {
  }
 
  if((address & 0x40e000) == 0x006000 //00-3f,80-bf:6000-7fff
- || (address & 0xf00000) == 0x400000 //40-4f:0000-ffff
+ || (address & 0xe00000) == 0x400000 //40-5f:0000-ffff
  || (address & 0xf00000) == 0x600000 //60-6f:0000-ffff
  ) {
  step();