Imported from GitHub: RomualdRousseau/Miniish · commit 83b337f · license GPL-3.0

Description

Homebrew 6502 Computer

README

Miniish - Homebrew 6502 Computer

The goal of this project is to build a 8bit game console based on 6502 CPU. The entire project is strongly inspired by the work and videos of Ben Eater, but also Javidx9 and his emulator.

Mother Board

It is basically the same hardware design presented by Ben Eater. I just cleaned up the adress control logic to have as mush of the 32K RAM available.

The address plan is:

0000 --------------------------------

// RAM

8000 --------------------------------

// LO ROM

D000 --------------------------------

// IRQ Status

D100 --------------------------------

// PICTURE PROCESSING UNIT (PORT1B)

D200 --------------------------------

// AUDIO PROCESSING UNIT (PORT2B)

D300 --------------------------------

// I/O

D400 --------------------------------

// Reserved

E000 --------------------------------

// HI ROM

FFFF --------------------------------

Picture Processing Unit (PPU)

VGA Card

The card is built using a FPGA and strongly inspired to the NES PPU and the capability of PICO-8.

The overall specs of the VGA card is 16 colors with a 128x128 display area using the VGA 640x480 60Hz standard. The 16 colors are the PICO8 palette.

The VGA card is interfaced to the motherboard through a sprite based unit. The video ram is not mapped to the computer ram but instead, the CPU sends instructions to a sprite generator very similar to the NES (greatly based on Javidx9 explanations).

The overall spec of the sprite generator is:

• 1 nametables for the background composed of 16 * 16 tiles. Each tile is 8x8 pixels. Scrolling vertical and horizontal modes are supported.

• 256 sprites with tansparency support. Each sprite is also a tile of 8x8 pixels.

• 64 simultaneous sprites on screen and 16 sprites per scanline

• NMI is generated at each vertical blank

Audio Procesing Unit (APU)

The card is built using a ATMEGA328p at 20Mhz with the library the_synth of Edgar.

The synthetizer has the overall spec:

• 4 channels at 20KHz

• 4 waveforms: triangle, square, sinus + noise

• 4 envelopes

• modulation

• IRQ0 is generated as the next data frame callback