First commit

Makefile

@@ -0,0 +1,18 @@
+CC = gcc
+
+CFLAGS = -O3
+
+default: cpu.o cpu.h emulate.c
+	$(CC) $(CFLAGS) cpu.o emulate.c -o A1Emu
+
+cpu.o: cpu.c cpu.h
+	$(CC) $(CFLAGS) -c cpu.c
+
+ifeq ($(OS),Windows_NT)
+clean:
+	del A1Emu.exe cpu.o
+else
+clean:
+	rm A1Emu cpu.o
+endif
+

cpu.h

@@ -0,0 +1,40 @@
+/*
+ * 6502 Emulator
+ *
+ * Spring Break programming project
+ * 
+ * 3/5/2019
+ * by Ben Jones
+ */
+
+#include <stdint.h>
+
+//Bits of the status register and correseponding flags
+#define CARRY 0
+#define ZERO 1
+#define INTERRUPT 2
+#define DECIMAL 3
+#define BREAK 4
+#define OVERFLOW 6
+#define NEGATIVE 7
+
+typedef struct CPU_6502 CPU_6502;
+
+//Store the state of cpu
+struct CPU_6502{
+	//The ALU loads and stores to and from the accumulator
+	uint8_t A_reg;
+	//Index registers
+	uint8_t X_reg;
+	uint8_t Y_reg;
+	//The stack pointer is actually a 16 bit value but the first byte is hard-wired to 0x01, so you only need 8 bits to store it
+	uint8_t SP_reg;
+	uint16_t PC_reg;
+	//The bits status register are all of the processor flags, but it is its own register whose value can be pushed to the stack
+	uint8_t P_reg;
+};
+
+
+void execute_6502(CPU_6502 *cpu, uint8_t (*read)(uint16_t), void (*write)(uint16_t, uint8_t));
+
+void reset_6502(CPU_6502 *cpu, uint8_t (*read)(uint16_t));

emulate.c

@@ -0,0 +1,137 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <conio.h>
+#include <sys/time.h>
+#include "cpu.h"
+
+unsigned DEBUG_STEP = 0;
+
+uint8_t memory[0x10000];
+
+void print_state(CPU_6502 cpu){
+	printf("A: %02x X:%02x Y:%02x SP:%02x P:%02x PC:%02x\n", (int) cpu.A_reg, (int) cpu.X_reg, (int) cpu.Y_reg, (int) cpu.SP_reg, (int) cpu.P_reg, (int) cpu.PC_reg);
+	printf("\nNext: %02x %02x %02x\n", (int) memory[cpu.PC_reg], (int) memory[cpu.PC_reg + 1], (int) memory[cpu.PC_reg + 2]);
+}
+
+//Special read memory routine for memory-mapped I/O
+uint8_t read_mem(uint16_t index){
+	uint8_t output;
+
+	if(DEBUG_STEP){
+		printf("READ: %04x ", index);
+	}
+	output = memory[index];
+	if(index == 0xD010){
+		memory[0xD011] &= 0x7F;
+	} else if((index&0xFF0F) == 0xD002){
+		output = 0;
+	}
+	if(DEBUG_STEP){
+		printf("%02x\n", memory[index]);
+	}
+	return output;
+}
+
+//Special write memory routine for memory mapped I/O
+void write_mem(uint16_t index, uint8_t value){
+	uint8_t x;
+	uint8_t y;
+
+	if(DEBUG_STEP){
+		printf("WRITE: %02x --> %04x\n", value, index);
+	}
+	if((index&0xFF0F) == 0xD002){
+		if((value&0x7F) == '\n' || (value&0x7F) == '\r'){
+			printf("\n");
+		} else if((value&0x7F) >= 0x20 && (value&0x7F) != 127){
+			//Output a character
+			printf("%c", value&0x7F);
+		}
+	}
+	memory[index] = value;
+}
+
+int main(){
+	CPU_6502 cpu;
+	FILE *fp;
+	unsigned char key_hit;
+	unsigned int count = 0;
+	unsigned long int last_time;
+	unsigned long int next_time;
+	struct timeval current_time;
+
+	cpu.A_reg = 0;
+	cpu.X_reg = 0;
+	cpu.Y_reg = 0;
+	cpu.SP_reg = 0;
+	cpu.P_reg = 0;
+	cpu.PC_reg = 0xE000;
+
+	//Load Integer Basic
+	fp = fopen("BASIC", "rb");
+	if(fp){
+		fread(memory + 0xE000, 1, 0x2000, fp);
+	} else {
+		printf("file error\n");
+		exit(1);
+	}
+	fclose(fp);
+	
+	//The emulator does not support ACI at the moment
+	
+	//Load Woz's monitor
+	fp = fopen("WOZMON", "rb");
+	if(fp){
+		fread(memory + 0xFF00, 1, 0x100, fp);
+	} else {
+		printf("file error 3\n");
+		exit(1);
+	}
+	fclose(fp);
+	reset_6502(&cpu, read_mem);//Reset the cpu
+	
+	//Initialize the timing
+	gettimeofday(&current_time, NULL);
+	last_time = current_time.tv_usec + current_time.tv_sec*1000000;
+	while(1){
+		/*Limit the speed of the processor to
+		 * a realistic 4usec per instruction
+		 *
+		 * Will count cpu cycles soon to make
+		 * better timing.
+		 */
+		do{
+			gettimeofday(&current_time, NULL);
+			next_time = current_time.tv_usec + current_time.tv_sec*1000000;
+		} while(next_time - last_time < 4);
+		last_time = last_time + 4;
+
+		//Execute the instruction
+		execute_6502(&cpu, read_mem, write_mem);
+		count = count + 1;
+		
+		//Debugging I/O
+		if(DEBUG_STEP){
+			print_state(cpu);
+			key_hit = getchar();
+			if(key_hit == '|'){
+				DEBUG_STEP = 0;
+			} else if(key_hit != ' '){
+				memory[0xD010] = key_hit|0x80;
+				memory[0xD011] = 0xFF;
+			}
+		}
+
+		//Handle keyboard I/O
+		if(!(count%200) && kbhit()){
+			key_hit = getch();
+
+			if(key_hit == '|'){
+				DEBUG_STEP = 1;
+			} else {
+				memory[0xD010] = key_hit|0x80;
+				memory[0xD011] |= 0x80;
+			}
+		}
+	}
+}