commit 02cbabcf2599e7acd58c5a0d14a5c99743d6248f
parent c53c1a51abe04bcd6755a74e5e493d46af93578b
Author: mjkloeckner <martin.cachari@gmail.com>
Date: Thu, 14 Jul 2022 01:59:05 -0300
All CPU adrressing modes and instruction fully implemented
CPU instructions and addressing modes are fully implemented.
The 6502_functional_test gets stuck at pc 0x05A4, so there is a bug in
there to solve for future commits.
The MEM_load_from_file function now loads the entire memory from the
provided file instead of only a part from address 0x8000 like before.
New function added: MEM_set_pc_start which sets the bytes that the pc
reads, when CPU_reset gets called, to the address passed as an argument.
Diffstat:
| M | 6502.c | | | 205 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------------ |
| M | 6502.h | | | 10 | +++++----- |
| M | main.c | | | 18 | ++++++++++++------ |
3 files changed, 191 insertions(+), 42 deletions(-)
diff --git a/6502.c b/6502.c
@@ -7,8 +7,8 @@ static MEM mem; /* 8 bit word */
static uint8_t cyc;
static uint8_t opc;
-static uint8_t tmp;
+static uint16_t tmp;
static uint16_t addr_abs;
static uint16_t addr_rel;
@@ -40,6 +40,7 @@ void CPU_reset(void) {
cpu.st = 0x00 | ST_FLAG_MASK[U];
/* 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);
@@ -54,7 +55,7 @@ void CPU_reset(void) {
}
void CPU_fetch(INS *ins) {
- *ins = decode[MEM_read(cpu.pc)];
+ *ins = decode[opc = MEM_read(cpu.pc)];
}
void CPU_exec(INS ins) {
@@ -78,11 +79,11 @@ void CPU_exec(INS ins) {
void CPU_irq(void) {
if(!CPU_get_flag(I)) {
/* requires two writes since `sp` is 8bits */
- MEM_write(0x100 + cpu.sp--, (cpu.pc >> 8) & 0x00FF);
+ MEM_write(0x100 + cpu.sp--, (cpu.pc & 0xFF00) >> 8);
MEM_write(0x100 + cpu.sp--, cpu.pc & 0x00FF);
- CPU_set_flag(I, 1);
MEM_write(0x100 + cpu.sp--, cpu.st);
+ CPU_set_flag(I, 1);
addr_abs = 0xFFFE;
uint16_t lo = MEM_read(addr_abs + 0);
@@ -144,12 +145,15 @@ void CPU_dump(void) {
void MEM_init(void) {
for(uint16_t i = 0; i < 0xFFFF; i++)
mem.ram[i] = 0;
+}
+void MEM_set_pc_start(uint16_t addr) {
/* First address that pc reads */
- mem.ram[0xFFFC] = 0x00;
- mem.ram[0xFFFD] = 0x80;
+ mem.ram[0xFFFC] = (addr & 0x00FF);
+ mem.ram[0xFFFD] = ((addr & 0xFF00) >> 8);
}
+
void MEM_load_from_file(char *path) {
FILE *fp;
@@ -158,7 +162,10 @@ void MEM_load_from_file(char *path) {
fp = fopen(path, "rb");
if(fp == NULL) return;
- fread(mem.ram + 0x8000, 1, 0x7FFF - 0x6, fp);
+ 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);
}
@@ -184,7 +191,7 @@ void MEM_dump_page(uint16_t page) {
printf("Page %04X:\n", page);
for(uint16_t i = page; i < (page + 0xFF); i++, j++)
- printf("%02X %s", mem.ram[i], (j % 0xF) ? "" : "\n");
+ printf("%02X %s", mem.ram[i], (j % 0x1E) ? "" : "\n");
putchar('\n');
}
@@ -261,7 +268,7 @@ uint8_t IND(void) {
/* assign the direction to ptr */
uint16_t ptr = (hi << 8) | lo;
- /* get the address contained in the address stored in ptr
+ /* get the address pointed by ptr
* and simulate page boundary hardware bug */
addr_abs = (MEM_read((ptr + (lo == 0x00FF) ? 1 : 0) & 0xFF00) << 8) | MEM_read(ptr);
@@ -332,13 +339,15 @@ uint8_t ZPY(void) {
/* Instructions */
uint8_t ADC(void) {
- uint8_t data = MEM_read(addr_abs);
+ uint16_t data = MEM_read(addr_abs);
+ uint16_t res = (cpu.ac + data + (uint16_t)CPU_get_flag(C));
- cpu.ac += (data + CPU_get_flag(C));
+ 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(Z, cpu.ac == 0);
- CPU_set_flag(N, cpu.ac & (1 << 7));
- CPU_set_flag(V, ((cpu.ac^data) & ~(cpu.ac^data)) & (1 << 7));
+ cpu.ac = (uint8_t)(res & 0x00FF);
return 1;
}
@@ -353,16 +362,27 @@ uint8_t AND(void) {
}
uint8_t ASL(void) {
+ tmp = (cpu.ac <<= 1);
+
+ 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;
}
uint8_t BCC(void) {
if(!CPU_get_flag(C)) {
+ cyc++;
addr_abs = cpu.pc + addr_rel;
/* if address changes page */
- if((addr_abs & (1 << 7)) != (cpu.pc & (1 << 7)))
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
cyc++;
cpu.pc = addr_abs;
@@ -373,10 +393,11 @@ uint8_t BCC(void) {
uint8_t BCS(void) {
if(CPU_get_flag(C)) {
+ cyc++;
addr_abs = cpu.pc + addr_rel;
/* if address changes page */
- if((addr_abs & (1 << 7)) != (cpu.pc & (1 << 7)))
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
cyc++;
cpu.pc = addr_abs;
@@ -387,10 +408,11 @@ uint8_t BCS(void) {
uint8_t BEQ(void) {
if(CPU_get_flag(Z)) {
+ cyc++;
addr_abs = cpu.pc + addr_rel;
/* if address changes page */
- if((addr_abs & (1 << 7)) != (cpu.pc & (1 << 7)))
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
cyc++;
cpu.pc = addr_abs;
@@ -400,15 +422,22 @@ uint8_t BEQ(void) {
}
uint8_t BIT(void) {
+ tmp = cpu.ac & MEM_read(cpu.pc);
+
+ CPU_set_flag(Z, tmp == 0);
+ CPU_set_flag(N, tmp & (1 << 7));
+ CPU_set_flag(V, tmp & (1 << 6));
+
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 & (1 << 7)) != (cpu.pc & (1 << 7)))
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
cyc++;
cpu.pc = addr_abs;
@@ -419,10 +448,11 @@ uint8_t BMI(void) {
uint8_t BNE(void) {
if(!CPU_get_flag(Z)) {
+ cyc++;
addr_abs = cpu.pc + addr_rel;
/* if address changes page */
- if((addr_abs & (1 << 7)) != (cpu.pc & (1 << 7)))
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
cyc++;
cpu.pc = addr_abs;
@@ -432,11 +462,12 @@ uint8_t BNE(void) {
}
uint8_t BPL(void) {
- if(!CPU_get_flag(N)) {
+ if(CPU_get_flag(N) == 0) {
+ cyc++;
addr_abs = cpu.pc + addr_rel;
/* if address changes page */
- if((addr_abs & (1 << 7)) != (cpu.pc & (1 << 7)))
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
cyc++;
cpu.pc = addr_abs;
@@ -446,20 +477,20 @@ uint8_t BPL(void) {
}
uint8_t BRK(void) {
- CPU_set_flag(B, 1);
-
- printf("break arrived\n");
CPU_irq();
+ CPU_set_flag(B, 1);
+
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 & (1 << 7)) != (cpu.pc & (1 << 7)))
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
cyc++;
cpu.pc = addr_abs;
@@ -470,10 +501,11 @@ uint8_t BVC(void) {
uint8_t BVS(void) {
if(CPU_get_flag(V)) {
+ cyc++;
addr_abs = cpu.pc + addr_rel;
/* if address changes page */
- if((addr_abs & (1 << 7)) != (cpu.pc & (1 << 7)))
+ if((addr_abs & 0xFF00) != (cpu.pc & 0xFF00))
cyc++;
cpu.pc = addr_abs;
@@ -503,19 +535,37 @@ uint8_t CLV(void) {
}
uint8_t CMP(void) {
+ tmp = MEM_read(addr_abs);
+
+ CPU_set_flag(C, cpu.ac >= tmp);
+ CPU_set_flag(Z, cpu.ac == tmp);
+ CPU_set_flag(N, cpu.ac & (1<<7));
+
return 0;
}
uint8_t CPX(void) {
+ tmp = MEM_read(addr_abs);
+
+ CPU_set_flag(C, cpu.x >= tmp);
+ CPU_set_flag(Z, cpu.x == tmp);
+ CPU_set_flag(N, cpu.x & (1<<7));
+
return 0;
}
uint8_t CPY(void) {
+ tmp = MEM_read(addr_abs);
+
+ CPU_set_flag(C, cpu.y >= tmp);
+ CPU_set_flag(Z, cpu.y == tmp);
+ CPU_set_flag(N, cpu.y & (1<<7));
+
return 0;
}
uint8_t DEC(void) {
- tmp = (MEM_read(addr_abs) - 1) & 0x00FF;
+ tmp = (MEM_read(addr_abs) - 1) & 0xFF;
MEM_write(addr_abs, tmp);
CPU_set_flag(Z, tmp == 0);
@@ -583,10 +633,18 @@ uint8_t INY(void) {
}
uint8_t JMP(void) {
+ cpu.pc = addr_abs;
return 0;
}
uint8_t JSR(void) {
+ cpu.pc--;
+
+ MEM_write(0x100 + cpu.sp--, (cpu.pc & 0xFF00) >> 8);
+ MEM_write(0x100 + cpu.sp--, (cpu.pc & 0x00FF));
+
+ cpu.pc = addr_abs;
+
return 0;
}
@@ -618,6 +676,17 @@ uint8_t LDY(void) {
}
uint8_t LSR(void) {
+ tmp = (cpu.ac >>= 1);
+
+ 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;
}
@@ -635,26 +704,61 @@ uint8_t ORA(void) {
}
uint8_t PHA(void) {
+ MEM_write(0x100 + cpu.sp--, cpu.ac);
+
return 0;
}
uint8_t PHP(void) {
+ MEM_write(0x100 + cpu.sp--, cpu.st);
+
return 0;
}
uint8_t PLA(void) {
+ cpu.ac = MEM_read(0x100 + ++cpu.sp);
+
+ CPU_set_flag(Z, (cpu.ac == 0));
+ CPU_set_flag(N, cpu.ac & (1 << 7));
+
return 0;
}
uint8_t PLP(void) {
+ cpu.st = MEM_read(0x100 + ++cpu.sp);
+
return 0;
}
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)
+ cpu.ac = (tmp & 0x00FF);
+ else
+ MEM_write(addr_abs, tmp & 0x00FF);
+
return 0;
}
uint8_t ROR(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)
+ cpu.ac = (tmp & 0x00FF);
+ else
+ MEM_write(addr_abs, tmp & 0x00FF);
+
return 0;
}
@@ -662,9 +766,6 @@ uint8_t RTI(void) {
/* restore cpu status register and increase stack pointer */
cpu.st = MEM_read(0x100 + ++cpu.sp);
- /* cpu.st &= ~ST_FLAG_MASK[B]; */
- CPU_set_flag(B, 0);
-
cpu.pc = MEM_read(0x100 + ++cpu.sp);
cpu.pc |= (MEM_read(0x100 + ++cpu.sp) << 8);
@@ -672,11 +773,26 @@ uint8_t RTI(void) {
}
uint8_t RTS(void) {
+ cpu.pc = MEM_read(0x100 + ++cpu.sp);
+ cpu.pc |= (MEM_read(0x100 + ++cpu.sp) << 8);
+
+ cpu.pc++;
+
return 0;
}
uint8_t SBC(void) {
- return 0;
+ uint8_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(C, ((res & 0xFF00) >> 7));
+ CPU_set_flag(V, ((cpu.ac^data) & ~(cpu.ac^data)) & (1 << 7));
+
+ cpu.ac = (uint8_t)(res & 0x00FF);
+
+ return 1;
}
uint8_t SEC(void) {
@@ -710,26 +826,53 @@ uint8_t STY(void) {
}
uint8_t TAX(void) {
+ cpu.x = cpu.ac;
+
+ CPU_set_flag(Z, cpu.x == 0);
+ CPU_set_flag(N, cpu.x & (1 << 7));
+
return 0;
}
uint8_t TAY(void) {
+ cpu.y = cpu.ac;
+
+ CPU_set_flag(Z, cpu.y == 0);
+ CPU_set_flag(N, cpu.y & (1 << 7));
+
return 0;
}
uint8_t TSX(void) {
+ cpu.x = cpu.sp;
+
+ CPU_set_flag(Z, cpu.x == 0);
+ CPU_set_flag(N, cpu.x & (1 << 7));
+
return 0;
}
uint8_t TXA(void) {
+ cpu.ac = cpu.x;
+
+ CPU_set_flag(Z, cpu.ac == 0);
+ CPU_set_flag(N, cpu.ac & (1 << 7));
+
return 0;
}
uint8_t TXS(void) {
+ cpu.sp = cpu.x;
+
return 0;
}
uint8_t TYA(void) {
+ cpu.ac = cpu.y;
+
+ CPU_set_flag(Z, cpu.y == 0);
+ CPU_set_flag(N, cpu.y & (1 << 7));
+
return 0;
}
diff --git a/6502.h b/6502.h
@@ -40,25 +40,25 @@ void CPU_init(void);
void CPU_reset(void);
void CPU_fetch(INS *ins);
void CPU_exec(INS ins);
-
void CPU_irq(void);
void CPU_nm_irq(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));
+
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);
+
void MEM_dump(void);
void MEM_dump_page(uint16_t page);
void MEM_dump_last_six(void);
void MEM_load_from_file(char *fp);
-uint8_t MEM_read(uint16_t addr);
-uint8_t MEM_write(uint16_t addr, uint8_t val);
-
/* Addresing modes */
uint8_t ABS(void);
diff --git a/main.c b/main.c
@@ -1,8 +1,10 @@
#include "6502.h"
#include <stdio.h>
+#include <stdlib.h>
-#define INPUT_FILE_PATH "10times3.bin"
+/* #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 */
@@ -14,27 +16,31 @@ int main (void) {
/* 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);
- /* Initialize registers to 0 */
+ /* Initialize cpu registers to 0 */
CPU_init();
+
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_last_six();
/* Execute instruction */
CPU_exec(ins);
-
- } while(getchar() != 'q');
+ } while(1);
+ /* } while(getchar() != 'q'); */
return 0;
}
