Evan Carlstrom - Computer Architecture

ls8/cpu.c

@@ -1,29 +1,41 @@
 #include "cpu.h"
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
 
 #define DATA_LEN 6
 
 /**
  * Load the binary bytes from a .ls8 source file into a RAM array
  */
-void cpu_load(struct cpu *cpu)
+void cpu_load(struct cpu *cpu, char *file)
 {
-  char data[DATA_LEN] = {
-    // From print8.ls8
-    0b10000010, // LDI R0,8
-    0b00000000,
-    0b00001000,
-    0b01000111, // PRN R0
-    0b00000000,
-    0b00000001  // HLT
-  };
-
+  // TODO: Replace this with something less hard-coded
+  FILE *file_pointer;
+  char line[1024];
   int address = 0;
 
-  for (int i = 0; i < DATA_LEN; i++) {
-    cpu->ram[address++] = data[i];
+  file_pointer = fopen(file, "r");
+  while(fgets(line, sizeof(line), file_pointer) != NULL) {
+    char *term;
+    unsigned char value;
+    value = strtoul(line, &term, 2);
+
+    if(value == HLT) {
+      cpu->ram[address++] = value;
+      break; /* only break case is when HLT instruction is received */
+    }
+
+    cpu->ram[address++] = value;
   }
+}
 
-  // TODO: Replace this with something less hard-coded
+unsigned char cpu_ram_read(struct cpu *cpu, unsigned char address) {
+    return cpu->ram[address]; /* reads the cpu struct's contents at this specific location in memory */
+  }
+
+void cpu_ram_write(struct cpu *cpu, unsigned char address, unsigned char value) {
+    cpu->ram[address] = value; /* set new data in memory */
 }
 
 /**
@@ -50,11 +62,97 @@ 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); /* IR = Instruction Register */
+
     // 2. Figure out how many operands this next instruction requires
+
+    /* commenting these out with CALL/RET, will enable usage without pre-loaded values)
+    unsigned char op0 = cpu_ram_read(cpu, cpu->PC + 1);
+    unsigned char op1 = cpu_ram_read(cpu, cpu->PC + 2);
+    */
+
+    unsigned char op0;
+    unsigned char op1;
+    unsigned int next;
+
     // 3. Get the appropriate value(s) of the operands following this instruction
+    if(IR & 0x80) {
+      op0 = cpu->ram[(cpu->PC + 1) & 0xff];
+      op1 = cpu->ram[(cpu->PC + 2) & 0xff];
+      next = 3;
+    }
+
+    else if(IR & 0x40) {
+      op0 = cpu->ram[(cpu->PC + 1) & 0xff];
+      next = 2;
+    }
     // 4. switch() over it to decide on a course of action.
+    /* case pseudocode for instruction handlers:
+    LDI -- set cpu->registers first value to next value
+    HLT -- set running to 0 and break
+    PRN -- print current register value (same as first value in LDI)
+    */
     // 5. Do whatever the instruction should do according to the spec.
+    switch(IR) {
+
+      case LDI:
+      {
+        cpu->registers[op0] = op1;
+        break;
+      }
+
+      case MUL:
+      {
+        cpu->registers[op0] *= cpu->registers[op1];
+        break;
+      }
+
+      case PRN:
+      {
+        printf("%d\n", cpu->registers[op0]);
+        break;
+      }
+
+      case POP:
+      {
+        cpu->registers[op0] = cpu_ram_read(cpu, cpu->registers[7]);
+        cpu->ram[cpu->registers[7]++] = 0x00;
+        break;
+      }
+
+      case PUSH:
+      {
+        cpu_ram_write(cpu, --cpu->registers[7], cpu->registers[op0]);
+        break;
+      }
+
+      case CALL:
+      {
+        cpu->ram[--cpu->registers[7]] = cpu->PC + next;
+        cpu->PC = cpu->registers[op0];
+        continue;
+      }
+
+      case RET:
+      {
+        cpu->PC = cpu->ram[cpu->registers[7]++];
+        continue;
+      }
+      case HLT:
+      {
+        running = 0;
+        break;
+      }
+
+      default:
+      {
+        printf("Command 0x%02x not recognized.\n", IR);
+        running = 0;
+        break;
+      }
+    }
     // 6. Move the PC to the next instruction.
+    cpu->PC = cpu->PC + next;
   }
 }
 
@@ -64,4 +162,9 @@ void cpu_run(struct cpu *cpu)
 void cpu_init(struct cpu *cpu)
 {
   // TODO: Initialize the PC and other special registers
+  /* need to initialize PC, registers, and ram (all elements of CPU struct) */
+
+  cpu->PC = 0;
+  memset(cpu->registers, 0, 8);
+  memset(cpu->ram, 0, 256);
 }

ls8/cpu.h

@@ -1,12 +1,18 @@
 #ifndef _CPU_H_
 #define _CPU_H_
 
+/* initial commit */
+
 // Holds all information about the CPU
 struct cpu {
   // TODO
   // PC
+  unsigned char PC;
   // registers (array)
+  unsigned char registers[8]; /* covers R0-R7 */
   // ram (array)
+  unsigned char *ram[256];
+  unsigned char FL; /* flag for later use */
 };
 
 // ALU operations
@@ -24,10 +30,14 @@ enum alu_op {
 #define HLT  0b00000001
 #define PRN  0b01000111
 // TODO: more instructions here. These can be used in cpu_run().
-
+#define MUL  0b10100010
+#define PUSH 0b01000101
+#define POP  0b01000110
+#define CALL 0b01010000
+#define RET  0b00010001
 // Function declarations
 
-extern void cpu_load(struct cpu *cpu);
+extern void cpu_load(struct cpu *cpu, char *file);
 extern void cpu_init(struct cpu *cpu);
 extern void cpu_run(struct cpu *cpu);
 

ls8/ls8.c

@@ -1,16 +1,22 @@
 #include <stdio.h>
+#include <stdlib.h>
 #include "cpu.h"
 
 /**
  * Main
  */
-int main(void)
+int main(int argc, char *argv[])
 {
   struct cpu cpu;
 
   cpu_init(&cpu);
-  cpu_load(&cpu);
+  cpu_load(&cpu, argv[1]);
   cpu_run(&cpu);
 
+  if(argc != 2) {
+    fprintf(stderr, "Usage: ls8 file.ls8\n");
+    return 1;
+  }
+
   return 0;
 }