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CPU Core Updates.

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Overflowing/Underflowing A or B with increment or decrement instructions now sets the Carry Flag.
An increment or decrement of A or B that doesn't result in an overflow/underflow now clears the Carry Flag.
Q is no longer saved and restored in subroutine calls, allowing it to be used to return a one byte result.
Documentation updated with more detail.
This commit is contained in:
Anachronaut
2024-11-20 13:57:57 -05:00
committed by GitHub
parent bf7beec8ec
commit e763a3e4de
2 changed files with 51 additions and 38 deletions
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Source/Emulator/cpu.c
+24 -29
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@@ -43,9 +43,6 @@ void genericCall(CPURegisters *cpu){
cpu->StackPointer--;
cpu->Data[cpu->StackPointer] = (cpu->DataPointer >> 8) & 0xFF;
cpu->StackPointer--;
// Push Q to the Stack.
cpu->Data[cpu->StackPointer] = cpu->Q;
cpu->StackPointer--;
// Push B to the Stack.
cpu->Data[cpu->StackPointer] = cpu->B;
cpu->StackPointer--;
@@ -159,29 +156,6 @@ uint8_t executeOperation(uint8_t Instruction, CPURegisters *cpu) {
// CALL - Push the Program Counter to the Stack, and perform an immediate branch.
genericCall(cpu);
break;
// case 0x18:
// // CALLA
// if (cpu->A == 0) {
// genericCall(cpu);
// }
// break;
// case 0x19:
// // CALLB
// if (cpu->B == 0) {
// genericCall(cpu);
// }
// break;
// case 0x1A:
// // CALLQ
// if (cpu->Q == 0) {
// genericCall(cpu);
// }
// case 0x1B:
// // CALLCF
// if (cpu->Status & 0x01) {
// genericCall(cpu);
// }
// break;
case 0x1F:
// RET - Return from subroutine, restore the registers and set the Program Counter to the Return Address.
// Pop A from the Stack.
@@ -190,9 +164,6 @@ uint8_t executeOperation(uint8_t Instruction, CPURegisters *cpu) {
// Pop B from the Stack.
cpu->StackPointer++;
cpu->B = cpu->Data[cpu->StackPointer];
// Pop Q from the Stack.
cpu->StackPointer++;
cpu->Q = cpu->Data[cpu->StackPointer];
// Pop the Data Pointer from the Stack.
cpu->StackPointer++;
cpu->DataPointer = (uint16_t)cpu->Data[cpu->StackPointer] << 8;
@@ -220,18 +191,42 @@ uint8_t executeOperation(uint8_t Instruction, CPURegisters *cpu) {
break;
case 0x22:
// INCA - Add 1 to A.
// Set the Carry Flag if the register overflows.
if (cpu->A == 0xFF) {
cpu->Status |= 0x01;
} else {
cpu->Status &= ~0x01;
}
cpu->A++;
break;
case 0x23:
// INCB - Add 1 to B.
// Set the Carry Flag if the register overflows.
if (cpu->B == 0xFF) {
cpu->Status |= 0x01;
} else {
cpu->Status &= ~0x01;
}
cpu->B++;
break;
case 0x24:
// DECA - Subtract 1 from A.
// Set the Carry Flag if the register underflows.
if (cpu->A == 0x00) {
cpu->Status |= 0x01;
} else {
cpu->Status &= ~0x01;
}
cpu->A--;
break;
case 0x25:
// DECB - Subtract 1 from B.
// Set the Carry Flag if the register underflows.
if (cpu->B == 0x00) {
cpu->Status |= 0x01;
} else {
cpu->Status &= ~0x01;
}
cpu->B--;
break;
case 0x26: