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synced 2024-08-19 17:29:34 +00:00
Fix stack in several ways
1. The stack should descend, not ascend; 2. The stack should be pushed byte for byte; meaning, when pushing P or A, those should consume one byte, not two; 3. The MSB should be pushed first when doing JSR and BRK, which makes some sense if you were reading the stack from $0100 - $01FF.
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@ -136,13 +136,13 @@ extern int mos6502_instruction(vm_8bit);
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extern mos6502 *mos6502_create(vm_segment *, vm_segment *);
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extern mos6502_instruction_handler mos6502_get_instruction_handler(vm_8bit);
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extern vm_16bit mos6502_get16(mos6502 *, size_t);
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extern vm_16bit mos6502_pop_stack(mos6502 *);
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extern vm_8bit mos6502_get(mos6502 *, size_t);
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extern vm_8bit mos6502_pop_stack(mos6502 *);
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extern void mos6502_execute(mos6502 *);
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extern void mos6502_free(mos6502 *);
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extern void mos6502_last_executed(mos6502 *, vm_8bit *, vm_8bit *, vm_16bit *);
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extern void mos6502_modify_status(mos6502 *, vm_8bit, int, int);
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extern void mos6502_push_stack(mos6502 *, vm_16bit);
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extern void mos6502_push_stack(mos6502 *, vm_8bit);
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extern void mos6502_set(mos6502 *, size_t, vm_8bit);
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extern void mos6502_set16(mos6502 *, size_t, vm_16bit);
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extern void mos6502_set_memory(mos6502 *, vm_segment *, vm_segment *);
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@ -254,7 +254,7 @@ apple2_reset(apple2 *mach)
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{
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mach->cpu->P = MOS_INTERRUPT;
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mach->cpu->PC = vm_segment_get16(mach->main, 0xFFFC);
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mach->cpu->S = 0;
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mach->cpu->S = 0xff;
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// Switch video mode back to 40 column text
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apple2_set_display(mach, DISPLAY_DEFAULT);
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@ -163,7 +163,7 @@ mos6502_create(vm_segment *rmem, vm_segment *wmem)
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cpu->X = 0;
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cpu->Y = 0;
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cpu->P = 0;
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cpu->S = 0;
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cpu->S = 0xff;
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return cpu;
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}
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@ -189,29 +189,29 @@ mos6502_free(mos6502 *cpu)
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* 256, addresses.
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*/
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void
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mos6502_push_stack(mos6502 *cpu, vm_16bit addr)
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mos6502_push_stack(mos6502 *cpu, vm_8bit addr)
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{
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mos6502_set16(cpu, 0x100 + cpu->S, addr);
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mos6502_set(cpu, 0x100 + cpu->S, addr);
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// And finally we need to increment S by 2 (since we've used two
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// bytes in the stack).
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cpu->S += 2;
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cpu->S--;
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}
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/*
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* Pop an address from the stack and return that.
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*/
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vm_16bit
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vm_8bit
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mos6502_pop_stack(mos6502 *cpu)
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{
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// The first thing we want to do here is to decrement S by 2, since
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// the value we want to return is two positions back.
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cpu->S -= 2;
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cpu->S++;
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// We need to use a bitwise-or operation to combine the hi and lo
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// bytes we retrieve from the stack into the actual position we
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// would use for the PC register.
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return mos6502_get16(cpu, 0x0100 + cpu->S);
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return mos6502_get(cpu, 0x0100 + cpu->S);
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}
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/*
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@ -14,7 +14,8 @@
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*/
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DEFINE_INST(brk)
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{
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mos6502_push_stack(cpu, cpu->PC);
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mos6502_push_stack(cpu, cpu->PC >> 8);
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mos6502_push_stack(cpu, cpu->PC & 0xff);
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mos6502_push_stack(cpu, cpu->P);
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cpu->P |= MOS_INTERRUPT;
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cpu->PC += 2;
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@ -36,7 +37,10 @@ DEFINE_INST(jmp)
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*/
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DEFINE_INST(jsr)
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{
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mos6502_push_stack(cpu, cpu->PC + 3);
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vm_16bit pc3 = cpu->PC + 3;
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mos6502_push_stack(cpu, pc3 >> 8);
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mos6502_push_stack(cpu, pc3 & 0xff);
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cpu->PC = cpu->eff_addr;
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}
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@ -57,6 +61,7 @@ DEFINE_INST(rti)
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{
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cpu->P = mos6502_pop_stack(cpu);
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cpu->PC = mos6502_pop_stack(cpu);
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cpu->PC |= mos6502_pop_stack(cpu) << 8;
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}
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/*
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@ -66,4 +71,5 @@ DEFINE_INST(rti)
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DEFINE_INST(rts)
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{
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cpu->PC = mos6502_pop_stack(cpu);
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cpu->PC |= mos6502_pop_stack(cpu) << 8;
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}
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