commit f5fb97645c1a7d2de0aef062f20a3f393fe5bfbc
parent 02cbabcf2599e7acd58c5a0d14a5c99743d6248f
Author: mjkloeckner <martin.cachari@gmail.com>
Date: Sat, 16 Jul 2022 01:57:12 -0300
General bug fixes
A lot of bugs has been fixed, using 6502_functional_test to get errors
and to see where errors has been made.
Now branch is independent from CPU_irq and CPU_nm_irq (Don't know if
it's the proper way) has it's own function body.
Two libraries has been included (unistd and string) for debugging
purposes, should be cleaned up in future commits.
Diffstat:
| M | 6502.c | | | 273 | ++++++++++++++++++++++++++++++++++++------------------------------------------- |
| M | 6502.h | | | 9 | ++++++++- |
| M | main.c | | | 23 | +++++++++++++++++------ |
3 files changed, 149 insertions(+), 156 deletions(-)
diff --git a/6502.c b/6502.c
@@ -2,6 +2,10 @@
#include <stdio.h>
+/* included for debugging purposes */
+#include <unistd.h>
+#include <string.h>
+
static CPU cpu;
static MEM mem; /* 8 bit word */
@@ -33,32 +37,27 @@ void CPU_init(void) {
}
void CPU_reset(void) {
- /* simulate 8 cycles needed to reset the cpu */
- do {
- if(cyc == 0) {
- cpu.sp = 0xFF; /* first page */
- cpu.st = 0x00 | ST_FLAG_MASK[U];
+ cpu.sp = 0xFF;
+ 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);
+ /* 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);
- cpu.pc = (hi << 8) | lo;
+ cpu.pc = (hi << 8) | lo;
- addr_abs = addr_rel = opc = 0x0000;
+ addr_abs = addr_rel = opc = 0x0000;
- cyc = 8;
- }
- cyc--;
- } while(cyc != 0);
+ /* simulate 8 cycles needed to reset the cpu */
+ cyc = 8;
}
void CPU_fetch(INS *ins) {
*ins = decode[opc = MEM_read(cpu.pc)];
}
-void CPU_exec(INS ins) {
+uint8_t CPU_exec(INS ins) {
/* simulate instructions cycles */
do {
if(cyc == 0) {
@@ -66,44 +65,47 @@ void CPU_exec(INS ins) {
cyc = ins.cycles;
+ if(!strcmp(ins.name, "???")) return 1;
uint8_t add_cyc_0 = ins.mode();
uint8_t add_cyc_1 = ins.op();
cyc += add_cyc_0 & add_cyc_1;
}
- cyc--;
- } while(cyc != 0);
+ } while(--cyc);
+
+ return 0;
}
/* interrupt request */
void CPU_irq(void) {
if(!CPU_get_flag(I)) {
- /* requires two writes since `sp` is 8bits */
- MEM_write(0x100 + cpu.sp--, (cpu.pc & 0xFF00) >> 8);
+ /* save pc */
+ MEM_write(0x100 + cpu.sp--, (cpu.pc >> 8) & 0x00FF);
MEM_write(0x100 + cpu.sp--, cpu.pc & 0x00FF);
- MEM_write(0x100 + cpu.sp--, cpu.st);
+ /* save st */
+ MEM_write(0x100 + cpu.sp--, cpu.st | (1 << 4) | (1 << 5));
+
CPU_set_flag(I, 1);
- addr_abs = 0xFFFE;
- uint16_t lo = MEM_read(addr_abs + 0);
- uint16_t hi = MEM_read(addr_abs + 1);
+ uint16_t lo = MEM_read(0xFFFE);
+ uint16_t hi = MEM_read(0xFFFF);
- cpu.pc = (hi << 8) | lo;
+ cpu.pc = ((hi << 8) & 0xFF00) | (lo & 0x00FF);
- cyc = 7;
+ cyc = 8;
}
}
/* non maskeable interrupt request */
void CPU_nm_irq(void) {
- /* requires two writes since `sp` is 8bits */
+ /* save program counter to stack */
MEM_write(0x100 + cpu.sp--, (cpu.pc >> 8) & 0x00FF);
MEM_write(0x100 + cpu.sp--, cpu.pc & 0x00FF);
- CPU_set_flag(B, 0);
+ /* save cpu status to stack */
+ MEM_write(0x100 + cpu.sp--, cpu.st | (1 << 4) | (1 << 5));
CPU_set_flag(I, 1);
- MEM_write(0x100 + cpu.sp--, cpu.st);
addr_abs = 0xFFFA;
uint16_t lo = MEM_read(addr_abs + 0);
@@ -114,6 +116,17 @@ void CPU_nm_irq(void) {
cyc = 8;
}
+void CPU_branch(void) {
+ cyc++;
+ addr_abs = cpu.pc + addr_rel;
+
+ /* if address changes page */
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
+ cyc++;
+
+ cpu.pc = addr_abs;
+}
+
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]);
}
@@ -141,6 +154,10 @@ void CPU_dump(void) {
printf(" pc: %04X -> %02X (%s)(%s)\n\n", cpu.pc, mem.ram[cpu.pc], aux.name, CPU_mode_name(aux.mode));
}
+uint16_t CPU_get_pc(void) {
+ return cpu.pc;
+}
+
/* Memory methods */
void MEM_init(void) {
for(uint16_t i = 0; i < 0xFFFF; i++)
@@ -148,12 +165,10 @@ void MEM_init(void) {
}
void MEM_set_pc_start(uint16_t addr) {
- /* First address that pc reads */
mem.ram[0xFFFC] = (addr & 0x00FF);
mem.ram[0xFFFD] = ((addr & 0xFF00) >> 8);
}
-
void MEM_load_from_file(char *path) {
FILE *fp;
@@ -162,9 +177,7 @@ void MEM_load_from_file(char *path) {
fp = fopen(path, "rb");
if(fp == NULL) return;
- printf("Loading %ld bytes from file `%s`\n", sizeof(mem.ram), path);
fread(mem.ram, 1, sizeof(mem.ram), fp);
- printf("Loading done\n");
/* fread(mem.ram + 0x8000, 1, 0x7FFF - 0x6, fp); */
fclose(fp);
@@ -190,7 +203,7 @@ void MEM_dump_page(uint16_t page) {
uint16_t j = 1;
printf("Page %04X:\n", page);
- for(uint16_t i = page; i < (page + 0xFF); i++, j++)
+ for(uint16_t i = page; i <= (page + 0xFF); i++, j++)
printf("%02X %s", mem.ram[i], (j % 0x1E) ? "" : "\n");
putchar('\n');
@@ -235,6 +248,9 @@ uint8_t ABX(void) {
uint16_t hi = MEM_read(cpu.pc++);
addr_abs = (hi << 8) | lo;
+
+ 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;
return ((addr_abs & 0x00FF) != (hi << 8)) ? 1 : 0;
@@ -245,8 +261,10 @@ uint8_t ABY(void) {
uint16_t hi = MEM_read(cpu.pc++);
addr_abs = (hi << 8) | lo;
- addr_abs += cpu.y;
+ 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;
return ((addr_abs & 0x00FF) != (hi << 8)) ? 1 : 0;
}
@@ -266,11 +284,11 @@ uint8_t IND(void) {
uint16_t hi = MEM_read(cpu.pc++);
/* assign the direction to ptr */
- uint16_t ptr = (hi << 8) | lo;
+ uint16_t p = (hi << 8) | lo;
- /* get the address pointed by ptr
+ /* get the address pointed by p
* and simulate page boundary hardware bug */
- addr_abs = (MEM_read((ptr + (lo == 0x00FF) ? 1 : 0) & 0xFF00) << 8) | MEM_read(ptr);
+ addr_abs = (MEM_read((lo == 0xFF) ? (p & 0xFF00) : p + 1) << 8) | MEM_read(p);
return 0;
}
@@ -279,13 +297,10 @@ uint8_t IZX(void) {
uint8_t addr = MEM_read(cpu.pc++);
/* get a direction from memory */
- uint16_t lo = MEM_read((addr + cpu.x + 0) & 0xFF);
+ uint16_t lo = MEM_read((addr + cpu.x) & 0xFF);
uint16_t hi = MEM_read((addr + cpu.x + 1) & 0xFF);
- uint16_t ptr = (hi << 8) | lo;
-
- /* get the direction contained on the memory that we read */
- addr_abs = (MEM_read(ptr + 1) << 8) | MEM_read(ptr + 0);
+ addr_abs = ((hi << 8) & 0xFF00) | lo;
return 0;
}
@@ -294,10 +309,10 @@ uint8_t IZY(void) {
uint8_t addr = MEM_read(cpu.pc++);
/* get a direction from memory */
- uint16_t lo = MEM_read((addr + 0) & 0xFF);
- uint16_t hi = MEM_read((addr + 1) & 0xFF);
+ uint16_t lo = MEM_read(addr);
+ uint16_t hi = MEM_read(addr + 1);
- addr_abs = (hi << 8) | lo;
+ addr_abs = ((hi << 8) & 0xFF00) | lo;
addr_abs += cpu.y;
return ((addr_abs & 0xFF00) != (hi << 8)) ? 1 : 0;
@@ -315,23 +330,18 @@ uint8_t REL(void) {
/* read only the offset of the zero page */
uint8_t ZP0(void) {
addr_abs = MEM_read(cpu.pc++);
- addr_abs &= 0xFF;
return 0;
}
uint8_t ZPX(void) {
- addr_abs = MEM_read(cpu.pc + cpu.x);
- addr_abs &= 0xFF;
- cpu.pc++;
+ addr_abs = (MEM_read(cpu.pc++) + cpu.x) & 0x00FF;
return 0;
}
uint8_t ZPY(void) {
- addr_abs = MEM_read(cpu.pc + cpu.y);
- addr_abs &= 0xFF;
- cpu.pc++;
+ addr_abs = (MEM_read(cpu.pc++) + cpu.y) & 0x00FF;
return 0;
}
@@ -377,139 +387,84 @@ uint8_t ASL(void) {
}
uint8_t BCC(void) {
- if(!CPU_get_flag(C)) {
- cyc++;
- addr_abs = cpu.pc + addr_rel;
-
- /* if address changes page */
- if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
- cyc++;
-
- cpu.pc = addr_abs;
- }
+ if(!CPU_get_flag(C))
+ CPU_branch();
return 0;
}
uint8_t BCS(void) {
- if(CPU_get_flag(C)) {
- cyc++;
- addr_abs = cpu.pc + addr_rel;
-
- /* if address changes page */
- if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
- cyc++;
-
- cpu.pc = addr_abs;
- }
+ if(CPU_get_flag(C))
+ CPU_branch();
return 0;
}
uint8_t BEQ(void) {
- if(CPU_get_flag(Z)) {
- cyc++;
- addr_abs = cpu.pc + addr_rel;
-
- /* if address changes page */
- if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
- cyc++;
-
- cpu.pc = addr_abs;
- }
+ if(CPU_get_flag(Z))
+ CPU_branch();
return 0;
}
uint8_t BIT(void) {
- tmp = cpu.ac & MEM_read(cpu.pc);
+ tmp = (MEM_read(addr_abs) & 0x00FF);
- CPU_set_flag(Z, tmp == 0);
- CPU_set_flag(N, tmp & (1 << 7));
+ CPU_set_flag(Z, (cpu.ac & tmp) == 0);
CPU_set_flag(V, tmp & (1 << 6));
+ CPU_set_flag(N, tmp & (1 << 7));
return 0;
}
uint8_t BMI(void) {
- if(CPU_get_flag(N)) {
- cyc++;
- addr_abs = cpu.pc + addr_rel;
-
- /* if address changes page */
- if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
- cyc++;
-
- cpu.pc = addr_abs;
- }
+ if(CPU_get_flag(N))
+ CPU_branch();
return 0;
}
uint8_t BNE(void) {
- if(!CPU_get_flag(Z)) {
- cyc++;
- addr_abs = cpu.pc + addr_rel;
-
- /* if address changes page */
- if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
- cyc++;
-
- cpu.pc = addr_abs;
- }
+ if(!CPU_get_flag(Z))
+ CPU_branch();
return 0;
}
uint8_t BPL(void) {
- if(CPU_get_flag(N) == 0) {
- cyc++;
- addr_abs = cpu.pc + addr_rel;
-
- /* if address changes page */
- if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
- cyc++;
-
- cpu.pc = addr_abs;
- }
+ if(!CPU_get_flag(N))
+ CPU_branch();
return 0;
}
uint8_t BRK(void) {
- CPU_irq();
+ /* save program counter to stack */
+ MEM_write(0x100 + cpu.sp--, (cpu.pc >> 8) & 0x00FF);
+ MEM_write(0x100 + cpu.sp--, cpu.pc & 0x00FF);
+
+ /* save cpu status to stack */
+ MEM_write(0x100 + cpu.sp--, cpu.st | (1 << 4) | (1 << 5));
+ CPU_set_flag(I, 1);
- CPU_set_flag(B, 1);
+ uint16_t lo = MEM_read(0xFFFE);
+ uint16_t hi = MEM_read(0xFFFF);
+
+ cpu.pc = (hi << 8) | lo;
return 0;
}
uint8_t BVC(void) {
- if(!CPU_get_flag(V)) {
- cyc++;
- addr_abs = cpu.pc + addr_rel;
-
- /* if address changes page */
- if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
- cyc++;
-
- cpu.pc = addr_abs;
- }
+ if(!CPU_get_flag(V))
+ CPU_branch();
return 0;
}
uint8_t BVS(void) {
- if(CPU_get_flag(V)) {
- cyc++;
- addr_abs = cpu.pc + addr_rel;
-
- /* if address changes page */
- if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
- cyc++;
-
- cpu.pc = addr_abs;
- }
+ if(CPU_get_flag(V))
+ CPU_branch();
return 0;
}
@@ -535,31 +490,33 @@ uint8_t CLV(void) {
}
uint8_t CMP(void) {
- tmp = MEM_read(addr_abs);
+ tmp = (MEM_read(addr_abs) & 0x00FF);
+
+ printf("cmp: %d, acc: %d\n", tmp, cpu.ac);
CPU_set_flag(C, cpu.ac >= tmp);
CPU_set_flag(Z, cpu.ac == tmp);
- CPU_set_flag(N, cpu.ac & (1<<7));
+ CPU_set_flag(N, (cpu.ac - tmp) & (1<<7));
return 0;
}
uint8_t CPX(void) {
- tmp = MEM_read(addr_abs);
+ tmp = (MEM_read(addr_abs) & 0x00FF);
CPU_set_flag(C, cpu.x >= tmp);
CPU_set_flag(Z, cpu.x == tmp);
- CPU_set_flag(N, cpu.x & (1<<7));
+ CPU_set_flag(N, (cpu.x - tmp) & (1<<7));
return 0;
}
uint8_t CPY(void) {
- tmp = MEM_read(addr_abs);
+ tmp = (MEM_read(addr_abs) & 0x00FF);
CPU_set_flag(C, cpu.y >= tmp);
CPU_set_flag(Z, cpu.y == tmp);
- CPU_set_flag(N, cpu.y & (1<<7));
+ CPU_set_flag(N, (cpu.y - tmp) & (1<<7));
return 0;
}
@@ -604,7 +561,7 @@ uint8_t EOR(void) {
}
uint8_t INC(void) {
- tmp = MEM_read(addr_abs + 1);
+ tmp = MEM_read(addr_abs) + 1;
MEM_write(addr_abs, tmp);
@@ -710,7 +667,7 @@ uint8_t PHA(void) {
}
uint8_t PHP(void) {
- MEM_write(0x100 + cpu.sp--, cpu.st);
+ MEM_write(0x100 + cpu.sp--, cpu.st | (1 << 4) | (1 << 5));
return 0;
}
@@ -725,8 +682,16 @@ uint8_t PLA(void) {
}
uint8_t PLP(void) {
+ uint8_t B_is_set = CPU_get_flag(B);
+ uint8_t U_is_set = CPU_get_flag(U);
+
+ /* restore status */
cpu.st = MEM_read(0x100 + ++cpu.sp);
+ /* This two flags stay the same as before */
+ CPU_set_flag(B, B_is_set);
+ CPU_set_flag(U, U_is_set);
+
return 0;
}
@@ -763,9 +728,17 @@ uint8_t ROR(void) {
}
uint8_t RTI(void) {
- /* restore cpu status register and increase stack pointer */
+ uint8_t B_is_set = CPU_get_flag(B);
+ uint8_t U_is_set = CPU_get_flag(U);
+
+ /* restore status */
cpu.st = MEM_read(0x100 + ++cpu.sp);
+ /* This two flags stay the same as before */
+ CPU_set_flag(B, B_is_set);
+ CPU_set_flag(U, U_is_set);
+
+ /* restore pc */
cpu.pc = MEM_read(0x100 + ++cpu.sp);
cpu.pc |= (MEM_read(0x100 + ++cpu.sp) << 8);
@@ -776,6 +749,8 @@ uint8_t RTS(void) {
cpu.pc = MEM_read(0x100 + ++cpu.sp);
cpu.pc |= (MEM_read(0x100 + ++cpu.sp) << 8);
+ CPU_set_flag(B, 0);
+
cpu.pc++;
return 0;
@@ -870,8 +845,8 @@ uint8_t TXS(void) {
uint8_t TYA(void) {
cpu.ac = cpu.y;
- CPU_set_flag(Z, cpu.y == 0);
- CPU_set_flag(N, cpu.y & (1 << 7));
+ CPU_set_flag(Z, cpu.ac == 0);
+ CPU_set_flag(N, cpu.ac & (1 << 7));
return 0;
}
diff --git a/6502.h b/6502.h
@@ -39,7 +39,8 @@ typedef enum {
void CPU_init(void);
void CPU_reset(void);
void CPU_fetch(INS *ins);
-void CPU_exec(INS ins);
+uint8_t CPU_exec(INS ins);
+
void CPU_irq(void);
void CPU_nm_irq(void);
void CPU_set_flag(ST_FLAG flag, uint8_t val);
@@ -47,6 +48,12 @@ 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);
diff --git a/main.c b/main.c
@@ -2,6 +2,7 @@
#include <stdio.h>
#include <stdlib.h>
+#include <stdbool.h>
/* #define INPUT_FILE_PATH "10times3.bin" */
#define INPUT_FILE_PATH "6502_functional_test.bin"
@@ -10,6 +11,15 @@
/* 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) {
+ brk = true;
+ }
+}
+
+
int main (void) {
INS ins;
@@ -28,19 +38,20 @@ int main (void) {
CPU_reset();
do {
- system("clear");
/* Fetch an instruction and increment pc */
CPU_fetch(&ins);
CPU_dump();
MEM_dump_last_six();
- MEM_dump_page(0x0000);
- MEM_dump_page(0x0100);
+ /* MEM_dump_page(0x0000); */
+ /* MEM_dump_page(0x0100); */
/* Execute instruction */
- CPU_exec(ins);
- } while(1);
- /* } while(getchar() != 'q'); */
+ if(CPU_exec(ins) != 0) return 1;
+
+ CPU_brk(0x22D8);
+ printf("--------------------------------------------\n");
+ } while(brk ? (getchar() != 'q') : true);
return 0;
}
