Emulator 6502

An 6502 emulator. The CPU is emulated, but no memory devices are provided by default. Functions are available to add memory devices

Adding custom modules

Modules allow for custom devices to be registered in the system. For example, a keyboard controller. What makes modules special is that they receive ticks from the system.

Module definition

typedef struct {
    E86_ModuleFunction_Init init;
    E86_ModuleFunction_Finish finish;
    E86_ModuleFunction_Tick tick;
    uint32_t reset;
    uint32_t counter;
} E86_Module;

The init function is called when the module is initialized. If this function is NULL, then initialization is skipped

The finish function is called when the module is cleaned up. If this function is NULL, then cleanup is skipped

The tick function is called when the module's counter is zero. If this is NULL, then ticking will be skipped

The reset variable is used to set the counter variable when it reaches zero

The counter variable is decremented when the system ticks

Module callback function signatures

typedef void (*E86_ModuleFunction_Init)();
typedef void (*E86_ModuleFunction_Finish)();
typedef void (*E86_ModuleFunction_Tick)();

Registering modules

To register a module, call

void E65_ModuleAdd(E65_Module* module);

The E65_ModuleAdd copies the module definition so the original definition is allowed to go out of scope

Memory functions

Custom memory functions can be registered to allow the CPU to interact with your custom modules. Functions are also available to read/write to memory

Registering memory

void E65_MemoryRegisterReadByte(E65_MemoryFunction_ReadByte func);
void E65_MemoryRegisterWriteByte(E65_MemoryFunction_WriteByte func);

Memory registration read/write function signatures

typedef E65_Byte (*E65_MemoryFunction_ReadByte)(E65_Word address);
typedef void (*E65_MemoryFunction_WriteByte)(E65_Word address, E65_Byte value);

Memory read/write function

E65_Byte E65_MemoryReadByte(E65_Word address);
void E65_MemoryWriteByte(E65_Word address, E65_Byte value);

Interrupts

There are two types are interrupts, non-maskable interrupt, called NMInterrupts in code, and interrupts. There are two functions used to set interrupts

Interrupts

Interrupts are level triggered in real hardware so there is a single function that can be used to set/reset the interrupt

void E65_InterruptSetInterrupt(bool interrupt);

NMInterrupts

NMInterrupts are edge triggered in real hardware so there is a single function to set the NMInterrupt

void E65_InterruptTriggerNMInterrupt();

Example

A simple example is provided which calculates the fibonacci sequence up to 13. The result can be see by hex dumping OUT.bin

Build

Scons is used as the build system

Installing scons

python3 -m pip install scons

Building

scons

To build with more than one thread, use -jN, where N is the number of threads. To clean the build, use -c

Additional flags

Two additional flags can be used debug and example. They can be used as so

scons debug=true example=true