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initial code for the opcodes

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This commit is contained in:
Thiago Auler 2017-11-13 21:13:20 -02:00
parent c39eaab7d9
commit f23c89dfce
3 changed files with 103 additions and 8 deletions
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4
src/6502.c
View File

@ -115,7 +115,7 @@ void execute()
case EOR: return eor();
case INC: return inc();
case JMP: return jmp();
case JPA: return jmp();
case JPA: return jpa();
case LDA: return lda();
case LDX: return ldx();
case LDY: return ldy();
@ -132,7 +132,7 @@ void execute()
void run()
{
while (pc != 0)
while (1)
{
fetch();
decode();

31
src/inc/opcodes.h
View File

@ -8,6 +8,7 @@ db ac; // accumulator
db x; // x register
db y; // y register
db sp; // stack pointer
db sr; // status register
db ir; // intruction register
enum opcodes_table
@ -29,8 +30,7 @@ enum opcodes_list
RTS = 0x60, BVS = 0x70, BCC = 0x90, BCS = 0xB0, BNE = 0xD0, BEQ = 0xF0,
PHP = 0x08, CLC = 0x18, PLP = 0x28, SEC = 0x38, PHA = 0x48, CLI = 0x58, PLA = 0x68, SEI = 0x78,
DEY = 0x88, TYA = 0x98, TAY = 0xA8, CLV = 0xB8, INY = 0xC8, CLD = 0xD8, INX = 0xE8, SED = 0xF8,
TXA = 0x8A, TXS = 0x9A, TAX = 0xAA, TSX = 0xBA, DEX = 0xCA, NOP = 0xEA,
XXX = 0xFF
TXA = 0x8A, TXS = 0x9A, TAX = 0xAA, TSX = 0xBA, DEX = 0xCA, NOP = 0xEA
};
enum address_mode
@ -55,7 +55,7 @@ am address_mode;
void adc(); // add memory to accumalator with carry
void and(); // and memory with accumulator
void asl(); // shift left one bit (memory on accumulator)
void asl(); // shift left one bit (memory or accumulator)
void bcc(); // branch on carry clear
void bcs(); // branch on carry set
void beq(); // branch on result zero
@ -80,7 +80,8 @@ void eor(); // exclusive-or memory with accumulator
void inc(); // increment memory by one
void inx(); // increment index x by one
void iny(); // increment index y by one
void jmp(); // jump to new location
void jmp(); // jump to new location (indirect)
void jpa(); // jump to new location (absolute)
void jsr(); // jump to new location saving return address
void lda(); // load accumulator with memory
void ldx(); // load index x with memory
@ -110,4 +111,26 @@ void txa(); // transfer index x to accumulator
void txs(); // transfer index x to stack pointer
void tya(); // transfer index y to accumulator
#define N_IS_SET (sr & 0b10000000) // negative
#define N_SET sr = sr | 0b10000000
#define N_UNSET sr = sr & 0b01111111
#define V_IS_SET (sr & 0b01000000) // overflow
#define V_SET sr = sr | 0b01000000
#define V_UNSET sr = sr & 0b10111111
#define B_IS_SET (sr & 0b00010000) // break
#define B_SET sr = sr | 0b00010000
#define B_UNSET sr = sr & 0b11101111
#define D_IS_SET (sr & 0b00001000) // decimal mode
#define D_SET sr = sr | 0b00001000
#define D_UNSET sr = sr & 0b11110111
#define I_IS_SET (sr & 0b00000100) // interrupt disabled
#define I_SET sr = sr | 0b00000100
#define I_UNSET sr = sr & 0b11111011
#define Z_IS_SET (sr & 0b00000010) // zero
#define Z_SET sr = sr | 0b00000010
#define Z_UNSET sr = sr & 0b11111101
#define C_IS_SET (sr & 0b00000001) // carry
#define C_SET sr = sr | 0b00000001
#define C_UNSET sr = sr & 0b11111110
#endif

76
src/opcodes.c
View File

@ -70,31 +70,55 @@ void fetch_operand()
void adc()
{
// add memory to accumalator with carry
fetch_operand();
ac = ac + operand + C_IS_SET;
}
void and()
{
// and memory with accumulator
fetch_operand();
ac = ac & operand;
}
void asl()
{
// shift left one bit (memory on accumulator)
// shift left one bit (memory or accumulator)
fetch_operand();
operand = operand << 1;
}
void bcc()
{
// branch on carry clear
if(!C_IS_SET)
{
address = read_byte(pc);
address = address + pc;
pc = address;
}
}
void bcs()
{
// branch on carry set
if(C_IS_SET)
{
address = read_byte(pc);
address = address + pc;
pc = address;
}
}
void beq()
{
// branch on result zero
if(Z_IS_SET)
{
address = read_byte(pc);
address = address + pc;
pc = address;
}
}
void bit()
@ -105,16 +129,34 @@ void bit()
void bmi()
{
// branch on result minus
if(N_IS_SET)
{
address = read_byte(pc);
address = address + pc;
pc = address;
}
}
void bne()
{
// branch on result not zero
if(!Z_IS_SET)
{
address = read_byte(pc);
address = address + pc;
pc = address;
}
}
void bpl()
{
// branch on result plus
if(!N_IS_SET)
{
address = read_byte(pc);
address = address + pc;
pc = address;
}
}
void brk()
@ -125,31 +167,47 @@ void brk()
void bvc()
{
// branch on overflow clear
if(!V_IS_SET)
{
address = read_byte(pc);
address = address + pc;
pc = address;
}
}
void bvs()
{
// branch on overflow set
if(V_IS_SET)
{
address = read_byte(pc);
address = address + pc;
pc = address;
}
}
void clc()
{
// clear carry flag
C_UNSET;
}
void cld()
{
// clear decimal mode
D_UNSET;
}
void cli()
{
// clear interrupt disable bit
I_UNSET;
}
void clv()
{
// clear overflow flag
V_UNSET;
}
void cmp()
@ -190,21 +248,35 @@ void eor()
void inc()
{
// increment memory by one
operand = operand + 1;
write_mem(address, operand);
}
void inx()
{
// increment index x by one
x = x + 1;
}
void iny()
{
// increment index y by one
y = y + 1;
}
void jmp()
{
// jump to new location
// jump to new location (indirect)
address = read_word(pc);
address = read_word(address);
pc = address;
}
void jpa()
{
// jump to new location (absolute)
address = read_word(pc);
pc = address;
}
void jsr()