Andre Myrick - Computer Architecture

ls8/cpu.c

@@ -1,7 +1,18 @@
 #include "cpu.h"
-
+#include <stdio.h>
+#include <string.h>
 #define DATA_LEN 6
 
+unsigned char cpu_ram_read(struct cpu *cpu, unsigned char address)
+{
+    return cpu->ram[address];
+}
+
+void cpu_ram_write(struct cpu *cpu, unsigned char address, unsigned char value)
+{
+    cpu->ram[address] = value;
+}
+
 /**
  * Load the binary bytes from a .ls8 source file into a RAM array
  */
@@ -50,9 +61,36 @@ void cpu_run(struct cpu *cpu)
   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
     // 3. Get the appropriate value(s) of the operands following this instruction
+    unsigned char operandA = cpu_ram_read(cpu, cpu->PC + 1);
+    unsigned char operandB = cpu_ram_read(cpu, cpu->PC + 2);
     // 4. switch() over it to decide on a course of action.
+    switch (ir)
+    {
+      case LDI:
+      {
+        cpu->registers[operandA] = operandB;
+        cpu->PC += 3;
+        break;
+      }
+      case PRN:
+      {
+        printf("%d\n", cpu->registers[operandA]);
+        cpu->PC += 2;
+        break;
+      }
+      case HLT:
+      {
+        running = 0;
+        break;
+      }
+      default:
+      {
+        break;
+      }
+    }
     // 5. Do whatever the instruction should do according to the spec.
     // 6. Move the PC to the next instruction.
   }
@@ -63,5 +101,7 @@ void cpu_run(struct cpu *cpu)
  */
 void cpu_init(struct cpu *cpu)
 {
-  // TODO: Initialize the PC and other special registers
+  cpu->PC = 0;
+  memset(cpu->ram, 0, 8 * sizeof(unsigned char));
+  memset(cpu->registers, 0, 256 * sizeof(unsigned char));
 }

ls8/cpu.h

@@ -5,8 +5,11 @@
 struct cpu {
   // TODO
   // PC
+  unsigned char PC;
   // registers (array)
+  unsigned char registers[8];
   // ram (array)
+  unsigned char ram[256];
 };
 
 // ALU operations