Asynchronous Circuit and System Design Group

Asynchronous Open-Source DLX Processor (ASPIDA)

Memory Details

The system has three types of memory:

Instruction memory
Data memory
Video memory (VRAM)

All of the above types are accesible by the CPU. The instruction memory is a read only memory as it is the place where the program is stored. The data memory is used as a read-write memory by the CPU. In order to calculate the next frame, the CPU reads the current state from the video memory and writes the next state to the video memory.

The VGA driver only has read access to the video memory. The VGA driver reads the current state of the video memory and displays it.

The instruction and the data memory share the same address space. The video memory is restricted to addresses above 0x1000.
Figure below illustrates how the address space of the memory is divided to the instruction memory, the data memory and the video memory.