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first commit #208

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61e2780
first commit
DavidBenavidez123 Mar 4, 2019
525c342
still working on mvp
DavidBenavidez123 Mar 7, 2019
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95 changes: 82 additions & 13 deletions ls8/cpu.c
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Original file line number Diff line number Diff line change
Expand Up @@ -8,18 +8,19 @@
void cpu_load(struct cpu *cpu)
{
char data[DATA_LEN] = {
// From print8.ls8
0b10000010, // LDI R0,8
0b00000000,
0b00001000,
0b01000111, // PRN R0
0b00000000,
0b00000001 // HLT
// From print8.ls8
0b10000010, // LDI R0,8
0b00000000,
0b00001000,
0b01000111, // PRN R0
0b00000000,
0b00000001 // HLT
};

int address = 0;

for (int i = 0; i < DATA_LEN; i++) {
for (int i = 0; i < DATA_LEN; i++)
{
cpu->ram[address++] = data[i];
}

Expand All @@ -31,10 +32,11 @@ void cpu_load(struct cpu *cpu)
*/
void alu(struct cpu *cpu, enum alu_op op, unsigned char regA, unsigned char regB)
{
switch (op) {
case ALU_MUL:
// TODO
break;
switch (op)
{
case ALU_MUL:
// TODO
break;

// TODO: implement more ALU ops
}
Expand All @@ -43,25 +45,92 @@ void alu(struct cpu *cpu, enum alu_op op, unsigned char regA, unsigned char regB
/**
* Run the CPU
*/

void push_to_stack(struct cpu *cpu, int val)
{
cpu->reg[7]--;
cpu->ram[cpu->reg[7]] = val;
}
unsigned char cpu_pop(struct cpu *cpu)
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@grantreighard grantreighard Mar 7, 2019

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Now you need to add PUSH and POP instructions to your switch statement.

{
unsigned char val = cpu_ram_read(cpu, cpu->reg[7]);
cpu->reg[7]++;
return val;
}

void cpu_run(struct cpu *cpu)
{
int running = 1; // True until we get a HLT instruction

while (running) {
while (running)
{
// TODO
// 1. Get the value of the current instruction (in address PC).
unsigned char IR = cpu_ram_read(cpu, cpu->pc);
// 2. Figure out how many operands this next instruction requires
//IR gives you the current instuction
//reading from the bitwise right shift will give you the number of operands:
unsigned char operandA = 0;
unsigned char operandB = 0;
unsigned int numOp = IR >> 6;
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@grantreighard grantreighard Mar 7, 2019

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Awesome job with this! Now you need to use it.


// 3. Get the appropriate value(s) of the operands following this instruction
if (numOp == 2)
{
unsigned char operandA = cpu_ram_read(cpu, (cpu->pc + 1) & 0xff);
unsigned char operandB = cpu_ram_read(cpu, (cpu->pc + 2) & 0xff);
}
// 4. switch() over it to decide on a course of action.
switch (IR)
{
case LDI:
// change the value of reg @ operanA to operandB;
printf("%d\n", cpu->reg[operandB]);
cpu->reg[operandA] = operandB;
cpu->pc += 2;
printf("%d\n", cpu->reg[operandB]);
break;
case PRN:
cpu->pc += 2;
printf("%d\n", cpu->reg[operandA]);
break;
case HLT:
running = 0;
break;
default:
printf("Error");
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@grantreighard grantreighard Mar 7, 2019

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You can make this error more verbose with the program counter and instruction code for better debugging.

break;
}
// 5. Do whatever the instruction should do according to the spec.
// 6. Move the PC to the next instruction.
}
}

// ram functions
unsigned char cpu_ram_read(struct cpu *cpu, unsigned char index)
{
return cpu->ram[index];
}

void cpu_ram_write(struct cpu *cpu, unsigned mar, unsigned char mdr)
{
cpu->ram[mar] = mdr;
}

/**
* Initialize a CPU struct
*/
void cpu_init(struct cpu *cpu)
{
// TODO: Initialize the PC and other special registers
for (int i = 0; i <= 6; i++)
{
cpu->reg[i] = 0;
}

cpu->reg[7] = 0;
cpu->pc = 0;

// set everything in ram to 0
memset(cpu->ram, 0, sizeof cpu->ram);
}
21 changes: 13 additions & 8 deletions ls8/cpu.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2,27 +2,32 @@
#define _CPU_H_

// Holds all information about the CPU
struct cpu {
struct cpu
{
// TODO
// PC
unsigned int pc;
// registers (array)
unsigned char reg[8];
// ram (array)
unsigned char ram[256];
};

// ALU operations
enum alu_op {
ALU_MUL
// Add more here
enum alu_op
{
ALU_MUL
// Add more here
};

// Instructions

// These use binary literals. If these aren't available with your compiler, hex
// literals should be used.

#define LDI 0b10000010
#define HLT 0b00000001
#define PRN 0b01000111
#define LDI 0b10000010
#define HLT 0b00000001
#define PRN 0b01000111
// TODO: more instructions here. These can be used in cpu_run().

// Function declarations
Expand All @@ -31,4 +36,4 @@ extern void cpu_load(struct cpu *cpu);
extern void cpu_init(struct cpu *cpu);
extern void cpu_run(struct cpu *cpu);

#endif
#endif