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3 Commits
a6f12814f9 ... b08c1e6ac4

Author SHA1 Message Date
Nobuhiro Hatano b08c1e6ac4
version 2.4.0 2022-04-09 10:20:01 +09:00
Nobuhiro Hatano edb994f74d
Merge pull request #2 from mtleblanc/emufixes 
Fix errors in 6502 emulation
 2022-04-09 09:30:49 +09:00
Michael LeBlanc 032aacee39 Fix errors in 6502 emulation 
This commit fixes the following behaviors:

Indirect X zero page addressing should always wrap and stay on zero page
BRK should disable interrupts
ADC in decimal mode should carry between nibbles based on adjusted,
  not original values.
Writes of status register to the stack should always set M and should
  set B on BRK/PHP and ~B on IRQ/NMI

Found and tested against
https://github.com/Klaus2m5/6502_65C02_functional_tests/blob/master/6502_functional_test.a65
 2022-04-08 10:44:51 -07:00
2 changed files with 19 additions and 7 deletions
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12
CHANGELOG
View File

@ -1,6 +1,18 @@
CHANGELOG
=========
2.4.0 mtleblanc's contribution:
- Indirect X zero page addressing should always wrap and stay on zero page
- BRK should disable interrupts
- ADC in decimal mode should carry between nibbles based on adjusted,
not original values.
- Writes of status register to the stack should always set M and should
set B on BRK/PHP and ~B on IRQ/NMI
- Given the above, status register does not need to track M or B bits,
removed from initialization.
- Found and tested against
https://github.com/Klaus2m5/6502_65C02_functional_tests
2.3.0
- ROM can be loaded from the directory of ROMDIR environment variable.

14
src/m6502.c
View File

@ -40,7 +40,7 @@
#define Z 0x02
#define C 0x01
static unsigned char accumulator, xRegister, yRegister, statusRegister = 0x24, stackPointer;
static unsigned char accumulator, xRegister, yRegister, statusRegister = I, stackPointer;
static int IRQ = 0, NMI = 0;
static unsigned short programCounter;
static unsigned char btmp;
@ -101,7 +101,7 @@ static void popProgramCounter(void)
static void handleIRQ(void)
{
pushProgramCounter();
memWrite((unsigned short)(0x100 + stackPointer), (unsigned char)(statusRegister & ~0x10));
memWrite((unsigned short)(0x100 + stackPointer), (unsigned char)((statusRegister & ~B) | M));
stackPointer--;
statusRegister |= I;
programCounter = memReadAbsolute(0xFFFE);
@ -111,7 +111,7 @@ static void handleIRQ(void)
static void handleNMI(void)
{
pushProgramCounter();
memWrite((unsigned short)(0x100 + stackPointer), (unsigned char)(statusRegister & ~0x10));
memWrite((unsigned short)(0x100 + stackPointer), (unsigned char)((statusRegister & ~B) | M));
stackPointer--;
statusRegister |= I;
NMI = 0;
@ -190,7 +190,7 @@ static void Ind(void)
static void IndZeroX(void)
{
ptr = xRegister + memRead(programCounter++);
ptr = (xRegister + memRead(programCounter++)) & 0xFF;
op = memRead(ptr);
op += memRead((unsigned short)((ptr + 1) & 0xFF)) << 8;
cycles += 3;
@ -319,7 +319,7 @@ static void ADC(void)
tmp = (Op1 & 0x0F) + (Op2 & 0x0F) + (statusRegister & C ? 1 : 0);
accumulator = tmp < 0x0A ? tmp : tmp + 6;
tmp = (Op1 & 0xF0) + (Op2 & 0xF0) + (tmp & 0xF0);
tmp = (Op1 & 0xF0) + (Op2 & 0xF0) + (accumulator & 0xF0);
if (tmp & 0x80)
statusRegister |= N;
@ -617,7 +617,7 @@ static void PHA(void)
static void PHP(void)
{
memWrite((unsigned short)(0x100 + stackPointer), statusRegister);
memWrite((unsigned short)(0x100 + stackPointer), statusRegister | B | M);
stackPointer--;
cycles++;
}
@ -641,7 +641,7 @@ static void BRK(void)
{
pushProgramCounter();
PHP();
statusRegister |= B;
statusRegister |= I;
programCounter = memReadAbsolute(0xFFFE);
cycles += 3;
}