commit 7d1aca9563c3a1e587df714027db50c735c8d3f1
parent f5fb97645c1a7d2de0aef062f20a3f393fe5bfbc
Author: mjkloeckner <martin.cachari@gmail.com>
Date: Sat, 23 Jul 2022 19:31:34 -0300
6502_functional_test.bin passed
All the logic of the cpu is fully implemented.
The code is full of printf's for debbuging purposes until a proper
system monitor is impemented.
The CPU now checks that an invalid instruction is not being executed, if
that is the case a msg gets printed and the CPU waits for user input;
the same occurs if the CPU catches a loop trap (like the ones that happen in the 6502_functional_test.bin)
In this commit ST_FLAG_MASK is no longer available since we could use only
the shift value
Now MEM_write returns the written value; this is useful in some function
that require the written value to set the CPU flags
CPU shifts Instructions gets modified since in previous commits this
weren't working; a lot of improvement can be done still since code gets
repeated sometimes
Diffstat:
| M | 6502.c | | | 157 | ++++++++++++++++++++++++++++++++++++++++++++++--------------------------------- |
| M | 6502.h | | | 34 | ++++++++++++++-------------------- |
| M | Makefile | | | 3 | ++- |
| M | main.c | | | 27 | +++++++++++++-------------- |
4 files changed, 121 insertions(+), 100 deletions(-)
diff --git a/6502.c b/6502.c
@@ -3,7 +3,6 @@
#include <stdio.h>
/* included for debugging purposes */
-#include <unistd.h>
#include <string.h>
static CPU cpu;
@@ -12,28 +11,18 @@ static MEM mem; /* 8 bit word */
static uint8_t cyc;
static uint8_t opc;
-static uint16_t tmp;
+static uint16_t tmp;
static uint16_t addr_abs;
static uint16_t addr_rel;
INS decode[0x100];
-
-static uint8_t ST_FLAG_MASK[] = {
- (1 << 0), /* Carry */
- (1 << 1), /* Zero */
- (1 << 2), /* Disable interrupts */
- (1 << 3), /* Decimal mode */
- (1 << 4), /* Break */
- (1 << 5), /* Unused */
- (1 << 6), /* Overflow */
- (1 << 7) /* Negative */
-};
-
+static INS prev_ins;
/* Cpu methods */
void CPU_init(void) {
cpu.ac = cpu.x = cpu.y = cpu.sp = cpu.st = 0;
cyc = opc = tmp = 0;
+ prev_ins = (INS) {"???", &NUL, &IMP, 7};
}
void CPU_reset(void) {
@@ -41,7 +30,6 @@ void CPU_reset(void) {
cpu.st = 0x00;
/* little endian */
- printf("pc: 0x%4X%4X\n", MEM_read(0xFFFD), MEM_read(0xFFFC));
uint16_t lo = MEM_read(0xFFFC);
uint16_t hi = MEM_read(0xFFFD);
@@ -60,15 +48,22 @@ void CPU_fetch(INS *ins) {
uint8_t CPU_exec(INS ins) {
/* simulate instructions cycles */
do {
- if(cyc == 0) {
- cpu.pc++;
+ if (cyc == 0) {
+ if (!strcmp(ins.name, "???")) {
+ printf("EXEC: invalid instruction reached\n");
+ return 1;
+ } else if (!strcmp(ins.name, "BNE") && !(strcmp(prev_ins.name, "BNE"))) {
+ printf("EXEC: consecutive BNE reached\n");
+ return 1;
+ }
+ cpu.pc++;
cyc = ins.cycles;
- if(!strcmp(ins.name, "???")) return 1;
uint8_t add_cyc_0 = ins.mode();
uint8_t add_cyc_1 = ins.op();
+ prev_ins = ins;
cyc += add_cyc_0 & add_cyc_1;
}
} while(--cyc);
@@ -128,11 +123,11 @@ void CPU_branch(void) {
}
void CPU_set_flag(ST_FLAG flag, uint8_t val) {
- cpu.st = val ? cpu.st | ST_FLAG_MASK[flag] : cpu.st & ~(ST_FLAG_MASK[flag]);
+ cpu.st = val ? cpu.st | (1 << flag) : cpu.st & ~(1 << flag);
}
uint8_t CPU_get_flag(ST_FLAG flag) {
- return ((cpu.st & ST_FLAG_MASK[flag]) >> flag);
+ return (cpu.st & (1 << flag)) >> flag;
}
void print_reg(uint8_t reg) {
@@ -151,7 +146,8 @@ void CPU_dump(void) {
print_reg(cpu.st);
printf(" y: %02X (%3d)\n", cpu.y, cpu.y);
printf(" sp: %02X\n", cpu.sp);
- printf(" pc: %04X -> %02X (%s)(%s)\n\n", cpu.pc, mem.ram[cpu.pc], aux.name, CPU_mode_name(aux.mode));
+ printf(" pc: %04X -> %02X (%s)(%s)\n", cpu.pc, mem.ram[cpu.pc], aux.name, CPU_mode_name(aux.mode));
+ printf("--------------------------------------------\n");
}
uint16_t CPU_get_pc(void) {
@@ -189,7 +185,7 @@ uint8_t MEM_read(uint16_t addr) {
uint8_t MEM_write(uint16_t addr, uint8_t val) {
mem.ram[addr] = val;
- return 0;
+ return val;
}
void MEM_dump() {
@@ -240,6 +236,8 @@ uint8_t ABS(void) {
uint16_t hi = MEM_read(cpu.pc++);
addr_abs = (hi << 8) | lo;
+
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
return 0;
}
@@ -252,6 +250,7 @@ uint8_t ABX(void) {
printf("address fetched: %04X\nx register: %02X\nend address: %04X (%02X)\n", addr_abs, cpu.x, addr_abs + cpu.x, MEM_read(addr_abs + cpu.x));
addr_abs += cpu.x;
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
return ((addr_abs & 0x00FF) != (hi << 8)) ? 1 : 0;
}
@@ -265,11 +264,13 @@ uint8_t ABY(void) {
printf("address fetched: %04X\ny register: %02X\nend address: %04X (%02X)\n", addr_abs, cpu.y, addr_abs + cpu.y, MEM_read(addr_abs + cpu.y));
addr_abs += cpu.y;
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
return ((addr_abs & 0x00FF) != (hi << 8)) ? 1 : 0;
}
uint8_t IMM(void) {
addr_abs = cpu.pc++;
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
return 0;
}
@@ -290,6 +291,7 @@ uint8_t IND(void) {
* and simulate page boundary hardware bug */
addr_abs = (MEM_read((lo == 0xFF) ? (p & 0xFF00) : p + 1) << 8) | MEM_read(p);
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
return 0;
}
@@ -302,6 +304,8 @@ uint8_t IZX(void) {
addr_abs = ((hi << 8) & 0xFF00) | lo;
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
+
return 0;
}
@@ -315,13 +319,17 @@ uint8_t IZY(void) {
addr_abs = ((hi << 8) & 0xFF00) | lo;
addr_abs += cpu.y;
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
+
return ((addr_abs & 0xFF00) != (hi << 8)) ? 1 : 0;
}
uint8_t REL(void) {
- addr_rel = MEM_read(cpu.pc++);
+ addr_rel = (MEM_read(cpu.pc++) & 0x00FF);
+ printf("REL: offset: %02X (%d)\n", addr_rel, (int8_t)addr_rel);
- if(addr_rel & (1 << 7))
+ /* signed byte */
+ if (addr_rel & (1 << 7))
addr_rel |= 0xFF00;
return 0;
@@ -329,20 +337,23 @@ uint8_t REL(void) {
/* read only the offset of the zero page */
uint8_t ZP0(void) {
- addr_abs = MEM_read(cpu.pc++);
+ addr_abs = (MEM_read(cpu.pc++) & 0x00FF);
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
return 0;
}
uint8_t ZPX(void) {
addr_abs = (MEM_read(cpu.pc++) + cpu.x) & 0x00FF;
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
return 0;
}
uint8_t ZPY(void) {
addr_abs = (MEM_read(cpu.pc++) + cpu.y) & 0x00FF;
+ printf("Address: %04X -> (%02X)\n", addr_abs, MEM_read(addr_abs));
return 0;
}
@@ -355,7 +366,7 @@ uint8_t ADC(void) {
CPU_set_flag(N, res & (1 << 7));
CPU_set_flag(Z, (res & 0x00FF) == 0);
CPU_set_flag(C, ((res & 0xFF00) >> 7));
- CPU_set_flag(V, ((cpu.ac ^ res) & ~(res ^ data)) & (1 << 7));
+ CPU_set_flag(V, ((cpu.ac^res) & ~(cpu.ac^data)) & (1 << 7));
cpu.ac = (uint8_t)(res & 0x00FF);
@@ -372,17 +383,20 @@ uint8_t AND(void) {
}
uint8_t ASL(void) {
- tmp = (cpu.ac <<= 1);
+ if(decode[opc].mode == &IMP) {
+ tmp = cpu.ac << 1;
+ CPU_set_flag(C, (cpu.ac & (1 << 7)));
+ cpu.ac = (tmp & 0x00FF);
+ }
+ else {
+ tmp = MEM_read(addr_abs) << 1;
+ CPU_set_flag(C, MEM_read(addr_abs) & (1 << 7));
+ MEM_write(addr_abs, tmp & 0x00FF);
+ }
- CPU_set_flag(C, (tmp & (1 << 8)) != 0);
CPU_set_flag(Z, tmp == 0);
CPU_set_flag(N, tmp & (1 << 7));
- if(decode[opc].mode == &IMP)
- cpu.ac = (tmp & 0x00FF);
- else
- MEM_write(addr_abs, tmp & 0x00FF);
-
return 0;
}
@@ -522,11 +536,10 @@ uint8_t CPY(void) {
}
uint8_t DEC(void) {
- tmp = (MEM_read(addr_abs) - 1) & 0xFF;
- MEM_write(addr_abs, tmp);
+ tmp = MEM_write(addr_abs, MEM_read(addr_abs) - 1) & 0x00FF;
CPU_set_flag(Z, tmp == 0);
- CPU_set_flag(N, tmp & 0xFF);
+ CPU_set_flag(N, tmp & (1 << 7));
return 0;
}
@@ -561,9 +574,7 @@ uint8_t EOR(void) {
}
uint8_t INC(void) {
- tmp = MEM_read(addr_abs) + 1;
-
- MEM_write(addr_abs, tmp);
+ tmp = MEM_write(addr_abs, MEM_read(addr_abs) + 1) & 0x00FF;
CPU_set_flag(Z, tmp == 0);
CPU_set_flag(N, tmp & (1 << 7));
@@ -633,17 +644,20 @@ uint8_t LDY(void) {
}
uint8_t LSR(void) {
- tmp = (cpu.ac >>= 1);
+ if(decode[opc].mode == &IMP) {
+ tmp = (cpu.ac >> 1);
+ CPU_set_flag(C, cpu.ac & 0x01);
+ cpu.ac = (tmp & 0x00FF);
+ }
+ else {
+ tmp = (MEM_read(addr_abs) >> 1);
+ CPU_set_flag(C, MEM_read(addr_abs) & 0x01);
+ MEM_write(addr_abs, tmp & 0x00FF);
+ }
- CPU_set_flag(C, (tmp & (1 << 8)) != 0);
CPU_set_flag(Z, tmp == 0);
CPU_set_flag(N, tmp & (1 << 7));
- if(decode[opc].mode == &IMP)
- cpu.ac = (tmp & 0x00FF);
- else
- MEM_write(addr_abs, tmp & 0x00FF);
-
return 0;
}
@@ -696,33 +710,46 @@ uint8_t PLP(void) {
}
uint8_t ROL(void) {
- tmp = (cpu.ac <<= 1);
- tmp = (tmp & 0xFF00) ? (tmp | 0x01) : (tmp & ~(0x01));
-
- CPU_set_flag(Z, tmp == 0);
- CPU_set_flag(N, tmp & (1 << 7));
- CPU_set_flag(C, (tmp & (1 << 8)) != 0);
+ if(decode[opc].mode == &IMP) {
+ tmp = (cpu.ac << 1) & 0xFE;
+ tmp |= CPU_get_flag(C);
- if(decode[opc].mode == &IMP)
+ CPU_set_flag(C, cpu.ac & (1 << 7));
cpu.ac = (tmp & 0x00FF);
- else
+ }
+ else {
+ tmp = (MEM_read(addr_abs) << 1) & 0xFE;
+ tmp |= CPU_get_flag(C);
+
+ CPU_set_flag(C, MEM_read(addr_abs) & (1 << 7));
MEM_write(addr_abs, tmp & 0x00FF);
+ }
+
+ CPU_set_flag(Z, tmp == 0);
+ CPU_set_flag(N, tmp & (1 << 7));
return 0;
}
uint8_t ROR(void) {
- tmp = (cpu.ac <<= 1);
- tmp = (tmp & 0xFF00) ? (tmp | 0x01) : (tmp & ~(0x01));
+ if(decode[opc].mode == &IMP) {
+ tmp = (cpu.ac >> 1) & 0x7F;
+ tmp |= (CPU_get_flag(C) << 7);
- CPU_set_flag(Z, tmp == 0);
- CPU_set_flag(N, tmp & (1 << 7));
- CPU_set_flag(C, (tmp & (1 << 8)) != 0);
+ CPU_set_flag(C, cpu.ac & 0x01);
- if(decode[opc].mode == &IMP)
cpu.ac = (tmp & 0x00FF);
- else
+ }
+ else {
+ tmp = (MEM_read(addr_abs) >> 1) & 0x7F;
+ tmp |= (CPU_get_flag(C) << 7);
+
+ CPU_set_flag(C, MEM_read(addr_abs) & 1);
MEM_write(addr_abs, tmp & 0x00FF);
+ }
+
+ CPU_set_flag(Z, tmp == 0);
+ CPU_set_flag(N, tmp & (1 << 7));
return 0;
}
@@ -757,13 +784,13 @@ uint8_t RTS(void) {
}
uint8_t SBC(void) {
- uint8_t data = MEM_read(addr_abs) ^ 0xFF;
+ uint16_t data = MEM_read(addr_abs) ^ 0xFF;
uint16_t res = (cpu.ac + data + (uint16_t)CPU_get_flag(C));
- CPU_set_flag(Z, cpu.ac == 0);
- CPU_set_flag(N, cpu.ac & (1 << 7));
+ CPU_set_flag(N, res & (1 << 7));
+ CPU_set_flag(Z, (res & 0x00FF) == 0);
CPU_set_flag(C, ((res & 0xFF00) >> 7));
- CPU_set_flag(V, ((cpu.ac^data) & ~(cpu.ac^data)) & (1 << 7));
+ CPU_set_flag(V, ((cpu.ac^res) & ~(cpu.ac^data)) & (1 << 7));
cpu.ac = (uint8_t)(res & 0x00FF);
diff --git a/6502.h b/6502.h
@@ -1,5 +1,5 @@
-#ifndef __6502_H__
-#define __6502_H__
+#ifndef _6502_H
+#define _6502_H
#include <stdint.h>
@@ -16,7 +16,6 @@ typedef struct {
uint16_t pc;
} CPU;
-
/* zero-page: fast shorter instructions
* first-page: stack;
* last-six bytes: used to store special addresses */
@@ -36,37 +35,32 @@ typedef enum {
N /* Negative */
} ST_FLAG;
-void CPU_init(void);
-void CPU_reset(void);
-void CPU_fetch(INS *ins);
+char *CPU_mode_name(uint8_t (*mode)(void));
+uint16_t CPU_get_pc(void);
uint8_t CPU_exec(INS ins);
-
+uint8_t CPU_get_flag(ST_FLAG flag);
+void CPU_branch(void);
+void CPU_dump(void);
+void CPU_fetch(INS *ins);
+void CPU_init(void);
void CPU_irq(void);
void CPU_nm_irq(void);
+void CPU_reset(void);
void CPU_set_flag(ST_FLAG flag, uint8_t val);
-uint8_t CPU_get_flag(ST_FLAG flag);
-
-void CPU_dump(void);
-char *CPU_mode_name(uint8_t (*mode)(void));
-uint16_t CPU_get_pc(void);
-
-/* This should not be called from outside of file 6502.c */
-void CPU_branch(void);
-void print_reg(uint8_t);
-
-
void MEM_init(void);
void MEM_set_pc_start(uint16_t addr);
uint8_t MEM_read(uint16_t addr);
-uint8_t MEM_write(uint16_t addr, uint8_t val);
-
+uint8_t MEM_write(uint16_t addr, uint8_t val); /* returns written value */
void MEM_dump(void);
void MEM_dump_page(uint16_t page);
void MEM_dump_last_six(void);
void MEM_load_from_file(char *fp);
+void print_reg(uint8_t);
+
+
/* Addresing modes */
uint8_t ABS(void);
uint8_t ABX(void);
diff --git a/Makefile b/Makefile
@@ -1,7 +1,8 @@
CC := gcc
CLIBS :=
CFLAGS := -Wall -Wshadow -pedantic -ansi -std=c99 -O3
-SRCS := $(wildcard *.c)
+# SRCS := $(wildcard *.c)
+SRCS := $(shell find ./ ! -name "shift.c" -name "*.c")
OBJS := $(SRCS:.c=.o)
TARGET := 6502
diff --git a/main.c b/main.c
@@ -4,54 +4,53 @@
#include <stdlib.h>
#include <stdbool.h>
-/* #define INPUT_FILE_PATH "10times3.bin" */
#define INPUT_FILE_PATH "6502_functional_test.bin"
-/* TODO: Finish with CPU instructions implementation */
-/* TODO: add support for command line arguments */
-/* TODO: add proper system monitor (memory dump, cpu registers) */
+/* TODO: Add support for command line arguments */
+/* TODO: Add proper system monitor (memory dump, cpu registers) */
static bool brk = false;
void CPU_brk(uint16_t pc) {
if(CPU_get_pc() == pc) {
+ printf("BRK: %2X reached\n", pc);
brk = true;
}
}
-
int main (void) {
INS ins;
/* Initialize memory to 0 */
MEM_init();
- /* set the first address that the pc should be set to */
- MEM_set_pc_start(0x0400);
-
/* Load program to memory */
MEM_load_from_file(INPUT_FILE_PATH);
+ /* set the first address that the pc should be set to */
+ MEM_set_pc_start(0x0400);
+
/* Initialize cpu registers to 0 */
CPU_init();
CPU_reset();
+ int c = 0;
do {
+ if(c == 'c') brk = false;
+ CPU_brk(0x336d);
+
/* Fetch an instruction and increment pc */
CPU_fetch(&ins);
CPU_dump();
- MEM_dump_last_six();
+ /* MEM_dump_last_six(); */
/* MEM_dump_page(0x0000); */
/* MEM_dump_page(0x0100); */
/* Execute instruction */
- if(CPU_exec(ins) != 0) return 1;
-
- CPU_brk(0x22D8);
- printf("--------------------------------------------\n");
- } while(brk ? (getchar() != 'q') : true);
+ if(CPU_exec(ins) != 0) brk = true;
+ } while(brk ? ((c = getchar()) != 'q') : true);
return 0;
}
