jake/SplitBit-Emulator
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Various bug fixes to assembler, added more data pointers.

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This commit is contained in:
Anachronaut
2026-08-13 23:41:22 -04:00
parent b50210d127
commit c2440ae5fa
38 changed files with 1028 additions and 236 deletions
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Source/Emulator/cpu.c
+76 -43
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@@ -14,7 +14,10 @@ void initializeCPU(CPURegisters *cpu, uint8_t *programMemory, uint8_t *dataMemor
cpu->Q = 0;
cpu->Status = 0;
cpu->ProgramCounter = 0x0000;
cpu->DataPointer = 0x0000;
// Every Data Pointer starts at the bottom of Data Memory.
for (int i = 0; i < DATA_POINTERS; i++) {
cpu->DataPointer[i] = 0x0000;
}
cpu->StackPointer = 0xFFFF;
cpu->Program = programMemory;
cpu->Data = dataMemory;
@@ -37,12 +40,16 @@ void genericCall(CPURegisters *cpu){
cpu->StackPointer--;
cpu->Data[cpu->StackPointer] = (cpu->ProgramCounter >> 8) & 0xFF;
cpu->StackPointer--;
// Push the Data Pointer to the Stack.
// Order, low byte, high byte
cpu->Data[cpu->StackPointer] = cpu->DataPointer & 0xFF;
cpu->StackPointer--;
cpu->Data[cpu->StackPointer] = (cpu->DataPointer >> 8) & 0xFF;
cpu->StackPointer--;
// Push the preserved Data Pointers to the Stack, lowest numbered first.
// Order within each one, low byte, high byte.
// The pointers above PRESERVED_DATA_POINTERS are deliberately left alone, so a
// subroutine can use one to hand an address back to whoever called it.
for (int i = 0; i < PRESERVED_DATA_POINTERS; i++) {
cpu->Data[cpu->StackPointer] = cpu->DataPointer[i] & 0xFF;
cpu->StackPointer--;
cpu->Data[cpu->StackPointer] = (cpu->DataPointer[i] >> 8) & 0xFF;
cpu->StackPointer--;
}
// Push B to the Stack.
cpu->Data[cpu->StackPointer] = cpu->B;
cpu->StackPointer--;
@@ -53,6 +60,15 @@ void genericCall(CPURegisters *cpu){
genericBranch(cpu);
}
uint16_t *selectDataPointer(CPURegisters *cpu) {
// Every instruction that works through a Data Pointer names which one in the
// byte immediately after the opcode. Out of range selectors are masked down
// rather than rejected, the way a narrow field in hardware would be. It is the
// assembler's job to refuse to emit one in the first place.
cpu->ProgramCounter++;
return &cpu->DataPointer[cpu->Program[cpu->ProgramCounter] & (DATA_POINTERS - 1)];
}
uint8_t executeOperation(uint8_t Instruction, CPURegisters *cpu) {
switch(Instruction) {
// 0x - Arithmetic and Logic Operations.
@@ -164,11 +180,15 @@ uint8_t executeOperation(uint8_t Instruction, CPURegisters *cpu) {
// Pop B from the Stack.
cpu->StackPointer++;
cpu->B = cpu->Data[cpu->StackPointer];
// Pop the Data Pointer from the Stack.
cpu->StackPointer++;
cpu->DataPointer = (uint16_t)cpu->Data[cpu->StackPointer] << 8;
cpu->StackPointer++;
cpu->DataPointer |= (uint16_t)cpu->Data[cpu->StackPointer];
// Pop the preserved Data Pointers from the Stack. This walks the pointers
// in the opposite order to genericCall, and takes the high byte before the
// low byte, so that it exactly mirrors the way they were pushed.
for (int i = PRESERVED_DATA_POINTERS - 1; i >= 0; i--) {
cpu->StackPointer++;
cpu->DataPointer[i] = (uint16_t)cpu->Data[cpu->StackPointer] << 8;
cpu->StackPointer++;
cpu->DataPointer[i] |= (uint16_t)cpu->Data[cpu->StackPointer];
}
// Pop the Return Address from the Stack.
cpu->StackPointer++;
cpu->ProgramCounter = (uint16_t)cpu->Data[cpu->StackPointer] << 8;
@@ -261,14 +281,16 @@ uint8_t executeOperation(uint8_t Instruction, CPURegisters *cpu) {
cpu->Data[cpu->StackPointer] = cpu->B;
cpu->StackPointer--;
break;
case 0x33:
// PSHD - Push the Data Pointer Address to the Stack.
case 0x33: {
// PSHD - Push the selected Data Pointer Address to the Stack.
// Order, high byte, low byte
// This ordering makes it easier to add offsets with register math.
cpu->Data[cpu->StackPointer] = (cpu->DataPointer >> 8) & 0xFF;
uint16_t pushed = *selectDataPointer(cpu);
cpu->Data[cpu->StackPointer] = (pushed >> 8) & 0xFF;
cpu->StackPointer--;
cpu->Data[cpu->StackPointer] = cpu->DataPointer & 0xFF;
cpu->Data[cpu->StackPointer] = pushed & 0xFF;
cpu->StackPointer--;
}
break;
case 0x34:
// POPA - Pop A from the Stack.
@@ -281,62 +303,70 @@ uint8_t executeOperation(uint8_t Instruction, CPURegisters *cpu) {
cpu->StackPointer++;
cpu->B = cpu->Data[cpu->StackPointer];
break;
case 0x36:
// POPD - Pop Data Address from the Stack.
case 0x36: {
// POPD - Pop a Data Address from the Stack into the selected Data Pointer.
uint16_t *popped = selectDataPointer(cpu);
cpu->StackPointer++;
cpu->DataPointer = (uint16_t)cpu->Data[cpu->StackPointer];
*popped = (uint16_t)cpu->Data[cpu->StackPointer];
cpu->StackPointer++;
cpu->DataPointer |= (uint16_t)cpu->Data[cpu->StackPointer] << 8;
*popped |= (uint16_t)cpu->Data[cpu->StackPointer] << 8;
}
break;
//
// 4x - Data Operations:
//
case 0x40:
// INCD - Increment Data Pointer.
cpu->DataPointer++;
// INCD - Increment the selected Data Pointer.
(*selectDataPointer(cpu))++;
break;
case 0x41:
// DECD - Decrement Data Pointer.
cpu->DataPointer--;
// DECD - Decrement the selected Data Pointer.
(*selectDataPointer(cpu))--;
break;
case 0x42:
// LDA - Load A from Data.
cpu->A = cpu->Data[cpu->DataPointer];
cpu->A = cpu->Data[*selectDataPointer(cpu)];
break;
case 0x43:
// LDB - Load B from Data.
cpu->B = cpu->Data[cpu->DataPointer];
cpu->B = cpu->Data[*selectDataPointer(cpu)];
break;
case 0x44:
// STQ - Store Q into Data.
cpu->Data[cpu->DataPointer] = cpu->Q;
cpu->Data[*selectDataPointer(cpu)] = cpu->Q;
break;
case 0x45:
// STA - Store A into Data.
cpu->Data[cpu->DataPointer] = cpu->A;
cpu->Data[*selectDataPointer(cpu)] = cpu->A;
break;
case 0x46:
// STB - Store B into Data.
cpu->Data[cpu->DataPointer] = cpu->B;
cpu->Data[*selectDataPointer(cpu)] = cpu->B;
break;
case 0x47:
// SETD - Set the Data Pointer.
case 0x47: {
// SETD - Set the selected Data Pointer.
uint16_t *destination = selectDataPointer(cpu);
cpu->ProgramCounter++;
uint16_t Address;
Address = (uint16_t)cpu->Program[cpu->ProgramCounter] << 8; // Cast the 8 bits to a 16 bit value and shift them to the high byte.
cpu->ProgramCounter++;
Address |= (uint16_t)cpu->Program[cpu->ProgramCounter];
cpu-> DataPointer = Address;
*destination = Address;
}
break;
case 0x48:
// DPUP - Offset the Data Pointer up by the value of the next byte of Program Memory.
case 0x48: {
// DPUP - Offset the selected Data Pointer up by the value of the next byte of Program Memory.
uint16_t *target = selectDataPointer(cpu);
cpu->ProgramCounter++;
cpu->DataPointer += cpu->Program[cpu->ProgramCounter];
*target += cpu->Program[cpu->ProgramCounter];
}
break;
case 0x49:
// DPDN - Offset the Data Pointer down by the value of the next byte of Program Memory.
case 0x49: {
// DPDN - Offset the selected Data Pointer down by the value of the next byte of Program Memory.
uint16_t *target = selectDataPointer(cpu);
cpu->ProgramCounter++;
cpu->DataPointer -= cpu->Program[cpu->ProgramCounter];
*target -= cpu->Program[cpu->ProgramCounter];
}
break;
//
// Dx - Output Operations:
@@ -383,10 +413,13 @@ uint8_t executeOperation(uint8_t Instruction, CPURegisters *cpu) {
// Unknown Instruction.
return 1;
}
if (cpu->DataPointer >= cpu->StackPointer) {
// A Stack Collision was detected.
cpu->Status |= 0x82; // Set Stack Collision Flag and Halt . (Bits 7 and 1 of the Status Register);
return 2;
}
return 0;
}
void stepCPU(CPURegisters *cpu) {
if (!(cpu->Status & 0x80)) {
// The CPU is not halted, so do a cycle.
executeOperation(cpu->Program[cpu->ProgramCounter], cpu);
cpu->ProgramCounter++;
}
}