109 lines
2.7 KiB
C
109 lines
2.7 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include "lib6502.h"
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/* Emulated OS functions. */
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#define WRCH 0xFFEE /* Write accumulator to stdout. */
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/* Write the accumulator to stdout. This function will be invoked
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* when the emulated program calls 0xFFEE.
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*/
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int wrch(M6502 *mpu, uint16_t address, uint8_t data)
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{
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int pc;
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/* Write the character.
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*/
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putchar(mpu->registers->a);
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/* We arrived here from a JSR instruction. The stack contains the
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* saved PC. Pop it off the stack.
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*/
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pc = mpu->memory[++mpu->registers->s + 0x100];
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pc |= mpu->memory[++mpu->registers->s + 0x100] << 8;
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/* The JSR instruction pushes the value of PC before it has been
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* incremented to point to the instruction after the JSR. Return PC
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* + 1 as the address for the next insn. Returning non-zero
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* indicates that we handled the 'subroutine' ourselves, and the
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* emulator should pretend the original 'JSR' neveer happened at
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* all.
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*/
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return pc + 1; /* JSR pushes next insn addr - 1 */
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}
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/* Exit gracefully. We arrange for this function to be called when
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* the emulator tries to transfer control to address 0.
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*/
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int done(M6502 *mpu, uint16_t address, uint8_t data)
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{
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char buffer[64];
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/* Dump the internal state of the processor.
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*/
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M6502_dump(mpu, buffer);
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/* Print a cute message and quit.
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*/
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printf("\nBRK instruction\n%s\n", buffer);
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exit(0);
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}
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int main()
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{
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M6502 *mpu = M6502_new(0, 0, 0); /* Make a 6502 */
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unsigned pc = 0x1000; /* PC for 'assembly' */
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/* Install the two callback functions defined above.
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*/
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M6502_setCallback(mpu, call, WRCH, wrch); /* Calling FFEE -> wrch() */
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M6502_setCallback(mpu, call, 0, done); /* Calling 0 -> done() */
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/* A few macros that dump bytes into the 6502's memory.
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*/
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# define gen1(X) (mpu->memory[pc++]= (uint8_t)(X))
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# define gen2(X,Y) gen1(X); gen1(Y)
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# define gen3(X,Y,Z) gen1(X); gen2(Y,Z)
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/* Hand-assemble the program.
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*/
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gen2(0xA2, 'A' ); // LDX #'A'
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gen1(0x8A ); // TXA
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gen3(0x20,0xEE,0xFF); // JSR FFEE
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gen1(0xE8 ); // INX
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gen2(0xE0, 'Z'+1 ); // CPX #'Z'+1
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gen2(0xD0, -9 ); // BNE 0x1002
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gen2(0xA9, '\n' ); // LDA #'\n'
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gen3(0x20,0xEE,0xFF); // JSR FFEE
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gen2(0x00,0x00 ); // BRK
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/* Just for fun: disssemble the program.
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*/
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{
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char insn[64];
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uint16_t ip= 0x1000;
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while (ip < pc)
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{
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int isz = M6502_disassemble(mpu, ip, insn);
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printf("%04X %s\n", ip, insn);
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ip += isz;
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}
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}
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/* Point the RESET vector at the first instruction in the assembled
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* program.
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*/
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M6502_setVector(mpu, RST, 0x1000);
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/* Reset the 6502 and run the program.
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*/
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M6502_reset(mpu);
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M6502_run(mpu);
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M6502_delete(mpu); /* We never reach here, but what the hey. */
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return 0;
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}
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