1.5 KiB
puce6502
This is a simple and readable emulation of the MOS 6502 CPU
It implements all original MOS6502 instructions, passes the Klaus Test Suite and is cycle accurate excepted for :
Absolute-X, absolute-Y, and Zero page-Y addressing modes which need an extra cycle if indexing crosses a page boundary, or if the instruction writes to memory.
You can easely interface it with your code using :
void puce6502Reset();
void puce6502Exec(long long int cycleCount);
The first emulates a reset signal, the second will execute as many instruction as needed to reach cycleCount
RAM and ROM are implemented using 8 bits integer arrays. And are directly accessible to your code to load ROM binary images and, for example, generate video output
RAM starts at adress 0x000
Update the three #define to adapt the ranges to your needs :
#define ROMSTART 0xD000
#define ROMSIZE 0x3000
#define RAMSIZE 0xC000
You are expected to provide a function to handle read and writes to locations not in ROM or in RAM (for Soft Switches, extension cards ROMs, PIA, VIA, ACIA etc...)
extern uint8_t softSwitches(uint16_t address, uint8_t value);
Finally, the variable ticks is a long long int holding the number of cycles since last reset.
For an example of use, you can refer to reinette II plus a french Apple II plus emulator.
Have fun !