diff options
Diffstat (limited to 'emu/6502.c')
| -rw-r--r-- | emu/6502.c | 68 |
1 files changed, 67 insertions, 1 deletions
@@ -252,16 +252,41 @@ void cpu_6502_step( cpu_6502_t *cpu ) update_negative_and_sign( cpu, cpu->A ); break; + case STX_ZERO: + operand8 = cpu_6502_read_byte( cpu, cpu->PC ); + cpu->PC++; + cpu_6502_write_byte( cpu, operand8, cpu->X ); + break; + case STX_ABS: operand16 = cpu_6502_read_word( cpu, cpu->PC ); cpu->PC += 2; cpu_6502_write_byte( cpu, operand16, cpu->X ); break; - + + case DEX_IMPL: + cpu->X--; + update_negative_and_sign( cpu, cpu->X ); + break; + case DEY_IMPL: cpu->Y--; update_negative_and_sign( cpu, cpu->Y ); break; + + case INY_IMPL: + cpu->Y++; + update_negative_and_sign( cpu, cpu->Y ); + break; + + case INC_IMPL: + operand8 = cpu_6502_read_byte( cpu, cpu->PC ); + cpu->PC++; + tmp = cpu_6502_read_byte( cpu, operand8 ); + tmp++; + cpu_6502_write_byte( cpu, operand8, tmp ); + update_negative_and_sign( cpu, tmp ); + break; case ROL_ACC: tmp = ( cpu->A << 1 ) | is_carry( cpu ); @@ -274,6 +299,36 @@ void cpu_6502_step( cpu_6502_t *cpu ) update_negative_and_sign( cpu, cpu->A ); break; + case CPX_IMM: + operand8 = cpu_6502_read_byte( cpu, cpu->PC ); + cpu->PC++; + tmp = ( cpu->X - operand8 ) & 0xFF; + if( cpu->X >= operand8 ) { + cpu->PS |= PS_C; + } else { + cpu->PS &= ~PS_C; + } + update_negative_and_sign( cpu, tmp ); + break; + + case SBC_IMM: + operand8 = cpu_6502_read_byte( cpu, cpu->PC ); + cpu->PC++; + tmp = cpu->A - operand8 - ( is_carry( cpu ) ? 0 : 1 ); + update_negative_and_sign( cpu, tmp ); + if( tmp & 0xFF00 ) { + cpu->PS |= PS_C; + } else { + cpu->PS &= ~PS_C; + } + if( ( ( cpu->A ^ tmp ) & 0x80 ) && ( ( cpu->A ^ operand8 ) & 0x80 ) ) { + cpu->PS |= PS_V; + } else { + cpu->PS &= ~PS_V; + } + cpu->A = tmp & 0xFF; + break; + case BNE_REL: operand8 = cpu_6502_read_byte( cpu, cpu->PC ); cpu->PC++; @@ -289,6 +344,14 @@ void cpu_6502_step( cpu_6502_t *cpu ) cpu->PC += (int8_t)operand8; } break; + + case BCS_REL: + operand8 = cpu_6502_read_byte( cpu, cpu->PC ); + cpu->PC++; + if( is_carry( cpu ) ) { + cpu->PC += (int8_t)operand8; + } + break; case JMP_ABS: cpu->PC = cpu_6502_read_word( cpu, cpu->PC ); @@ -308,6 +371,9 @@ void cpu_6502_step( cpu_6502_t *cpu ) cpu->SP = cpu->X; break; + case NOP_IMPL: + break; + default: fprintf( stderr, "ERROR: Illegal opcode %02X at PC %04X\n", opcode, cpu->PC ); exit( EXIT_FAILURE ); |