This is a very accurate 6502 emulator I wrote many years ago. It's very fast and small (although there are faster ones written in assembly), its structure is very clear and the code is commented.
If you are looking for an accurate MOS Technology 6502 CPU emulator for your project maybe you have found the correct one.
In order to compile you must install Z, a header only library which provides types, macros, inline functions, and a lot of utilities to detect the particularities of the compiler and the target system. This is the only dependency, the standard C library and its headers are not used and the emulator doesn't need to be dynamically linked with any library.
A Xcode project is provided to build the emulator. It has the following targets:
| Name | Description |
|---|---|
| dynamic | Shared library. |
| module | Module for A.C.M.E. |
| static | Static library. |
| static+ABI | Static library with a descriptive ABI to be used in modular multi-machine emulators. Building the ABI implies callback pointers with slots enabled. |
| static+ABI-API | The same as above but exposing only the symbol of the ABI, the API functions will be private. |
| Name | Description |
|---|---|
| CPU_6502_STATIC | You need to define this if you are using the emulator as a static library or if you have added its sources to your project. |
| CPU_6502_USE_SLOTS | Always needed when using the ABI. Each callback function will have its own context pointer, which should store the address of the object assigned to the call. |
| Name | Description |
|---|---|
| CPU_6502_DYNAMIC | Needed to build a shared library. Exports the public symbols. |
| CPU_6502_BUILD_ABI | Builds the ABI of type ZCPUEmulatorABI declared in the header with the identifier abi_emulation_cpu_6502. |
| CPU_6502_BUILD_MODULE_ABI | Builds a generic module ABI of type ZModuleABI. This constant enables CPU_6502_BUILD_ABI automatically so abi_emulation_cpu_6502 will be build too. This option is intended to be used when building a true module loadable at runtime with dlopen(), LoadLibrary() or similar. The module ABI can be accessed retrieving the weak symbol __module_abi__. |
| CPU_6502_HIDE_API | Makes the API functions private. |
| CPU_6502_HIDE_ABI | Makes the abi_emulation_cpu_6502 private. |
| CPU_6502_USE_LOCAL_HEADER | Use this if you have imported 6502.h and 6502.c to your project. 6502.c will include "6502.h" instead of <emulation/CPU/6502.h>. |
Description
Runs the CPU for the given number of cycles.
Prototype
zsize m6502_run(M6502 *object, zsize cycles);Parameters
object → A pointer to an emulator instance.
cycles → The number of cycles to be executed.
Return value
The number of cycles executed.
Discusion
Given the fact that one 6502 instruction needs between 2 and 7 cycles to be executed, it is not always possible to run the CPU the exact number of cycles specfified.
Description
Switchs the CPU power status.
Prototype
void m6502_power(M6502 *object, zboolean state);Parameters
object → A pointer to an emulator instance.
state → ON / OFF
Description
Resets the CPU by reinitializing its variables and sets its registers to the state they would be in a real 6502 CPU after a pulse in the RESET line.
Prototype
void m6502_reset(M6502 *object);Parameters
object → A pointer to an emulator instance.
Description
Performs a non-maskable interrupt. This is equivalent to a pulse in the NMI line of a real 6502 CPU.
Prototype
void m6502_nmi(M6502 *object);Parameters
object → A pointer to an emulator instance.
Description
Switchs the state of the maskable interrupt. This is equivalent to a change in the IRQ line of a real 6502 CPU.
Prototype
void m6502_irq(M6502 *object, zboolean state);Parameters
object → A pointer to an emulator instance.
state → ON = set line high, OFF = set line low
Before using an instance of the 6502 emulator, its cb structure must be initialized with the pointers to the callbacks that your program must provide in order to make possible for the CPU to access the emulated machine's memory.
Description
Called when the CPU needs to read 8 bits from memory.
Prototype
typedef zuint8 (* ZContext16BitAddressRead8Bit)(void *context, zuint16 address);
ZContext16BitAddressRead8Bit read;Parameters
context → A pointer to the calling emulator instance.
address → The memory address to read.
Return value
The 8 bits read from memory.
Description
Called when the CPU needs to write 8 bits to memory.
Prototype
typedef void (* ZContext16BitAddressWrite8Bit)(void *context, zuint16 address, zuint8 value);
ZContext16BitAddressWrite8Bit write;Parameters
context → A pointer to the calling emulator instance.
address → The memory address to write.
value → The value to write in address.
- v1.0.0 (2016-07-05)
- Initial release.
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