#6502 emulator c update#
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Performs an hardware reset, as done by the external pin of the real chip Triggers an Interrupt ReQuest?, as done by the external pin of the real chip Triggers a Non-Mascherable Interrupt request, as done by the external pin of the real chip

In such functions you can define your address decoding logic (if any) to address memory mapped I/O, external virtual devices and such. Respectively to read/write from/to a memory location (16 bit address, 8 bit value). Void MemoryWrite(uint16_t address, uint8_t value) It requires you to pass two external functions: The emulator comes as a single C++ class with five public methods:

#6502 emulator c code#

the opcode is used to address the instruction table) and the resulting code block is executed. The next instruction (the opcode value) is retrieved from memory. While(start + n > cycles & !illegalOpcode) ItвЂ™s a classic fetch-decode-execute loop: The illegals are not supported yet, so instead a simple NOP is executed.

#6502 emulator c software#

Such illegals were used to enforce software copy protection or to discover the exact CPU type. Such opcodes perform weird operations, write multiple registers at the same time, sometimes are the combination of two or more вЂњvalidвЂќ opcodes. opcode values other than the designed 151). Since the 6502 CPU uses 8 bit to encode the opcode value it also has a lot of вЂњillegal opcodesвЂќ (i.e. Uint16_t Addr_ABI() // ABSOLUTE INDIRECTДЄll the 151 opcodes are emulated. Uint16_t Addr_INY() // INDEXED-Y INDIRECT Uint16_t Addr_INX() // INDEXED-X INDIRECT Uint16_t Addr_ABY() // INDEXED-Y ABSOLUTE Uint16_t Addr_ABX() // INDEXED-X ABSOLUTE Uint16_t Addr_ZEY() // INDEXED-Y ZERO PAGE Uint16_t Addr_ZEX() // INDEXED-X ZERO PAGE My project is a simple jump-table based emulator: the actual value of the opcode (letвЂ™s say 0x80) is used to address a function pointer table, each entry of such table is a C++ function which emulates the behavior of the corresponding real instruction.ДЄll the 13 addressing modes are emulated: The switch-case based are the simpler ones but also the slowest: the opcode value is thrown inside a huge switch case which selects the code snippet to execute compilers can optimize switch case to reach near O(log(n)) complexity but they hardly do it when dealing with sparse integers (like most of the CPU opcode tables). The PLA/microcode based are the best as they offer both speed and limited complexity.

However the complexity of such emulators is non-linear with the number of transistors: in other word, you donвЂ™t want to emulate a modern Intel quad core using this approach!!! They emulate even the unwanted glitches, known and still unknown. Graph based emulators are the most accurate as they emulate the connections between transistors inside the die of the CPU. You can group all the CPU emulators out there in 4 main categories: Some theory behind emulators: emulator types

#6502 emulator c update#

However cycle accuracy is not yet implemented so mid-frame register update tricks cannot be reliably emulated. You can use this emulator in your machine emulator project. This CPU (and its many derivatives) powered machines such as:ДЄnd many other embedded devices still used today. So expect nearly 100% compliance with the real dealвЂ¦ at least on the normal behavior: as I said stuff like illegal opcodes or hardware glitches are currently not implemented. The emulator was extensively tested against this test suite:

hardware glitches, the known ones of course рџ™‚.

Interrupt and bus read/write operations are emulated as well. Some minor tricks have been introduced to greatly reduce the overall execution time. The code emulates a fully functional 6502 CPU and it seems to be pretty fast too.

The codebase has been moved into the Java 5 era (typesafe data structures, removal of obsolete methods, etc.This is my C++ emulator of the MOS Technology 6502 CPU.

added Run command, which steps until it hits a BRK instruction, a bad opcode or a breakpoint.

the file chooser now remembers the most recently used directory.

#6502 emulator c download#

You can download it at Д¬hanges from the original version include: The documentation still refers to version 1.0, but the program should be comprehensible as it is.

#6502 emulator c simulator#

This is a new version of Richard Russo's 6502 simulator called j6502. To run it, type orgasm -o output-file input-file, where input-file is a 6502 assembler file, and output-file is the generated object code. It can be used to generate object files for use with j6502. This is an OS X version of Robert Norris' 6502 assembler called Orgasm. An introduction to 6502 programming can be found at Machine Language For Beginners For those too young to remember, the 6502 powered computers such as the Apple //, the Atari 400/800, and various Commodore models like the PET-2001 and the C-64.