PET 2001 Emulator on STM32F103 BluePill

What?

This is a PET 2001 emulator running on a BluePill dev board. Written in Rust (and some inline assembly). Video is displayed via composite video. The emulated disk drive uses GD25Q64CSIG spi flash.

It's totally a just for fun personal project.

The emulation is probably not perfect and definitely pretty slow. As you can see in the video creating a nice replica of the original machine also was a non-goal. My original goal was to test the video output - everything else was just to have something interesting to display.

Here is a video of it in action: (click to open it on YouTube)

If you want to build the code you have to build it with the release profile - it won't work in debug mode.

Pins used

• PB8 Video to video via 680 ohms resitor

• PB9 Video-Sync to video via 330 ohms resistor

• PA0 Keyboard Select 1

• PA1 Keyboard Select 2

• PA2 Keyboard Select 3

• PA3 Keyboard Select 4

• PA4 Keyboard Select 5

• PA5 Keyboard Select 6

• PA6 Keyboard Select 7

• PA7 Keyboard Select 8

• PB0 Keyboard Input 1

• PB1 Keyboard Input 2

• PB10 Keyboard Input 3

• PB11 Keyboard Input 4

• PA8 Keyboard Input 5

• PA10 Keyboard Input 6

• PA11 Keyboard Input 7

• PA15 Keyboard Input 8

• PB3 Keyboard Input 9

• PB4 Keyboard Shift

SPI FLASH

• SCK = PB13 = 6
• MISO = PB14 = 2
• MOSI = PB15 = 5
• GND = 4
• VCC 3.3V = 8
• HOLD -> VCC -> 7
• WP -> VCC -> 3
• CS = PA9 = 1

Video

I used these sites to learn about this:

• http://www.batsocks.co.uk/readme/video_timing.htm
• https://github.com/eprive/STM32Lvideo
• https://github.com/eprive/STM32Lvideo/wiki

PB9 is controlled by TIM4

TIM1 is used as a "shock absorber" as outlined in https://github.com/abelykh0/VGA-demo-on-bluepill

Disk Emulation

This uses the SPI flash to save / load programs. In bluepet/src/bin/add_files.rs is some code to add a PET program. Unfortunately there isn't enough free memory to use the full 4k blocks of the flash so I "waste" 3/4 of each block unfortunately.

Keyboard

It's a usual matrix keyboard with 8 select lines and 9 data lines plus the shift keys (both connected to the same pin). I totally mixed up wires during soldering so the keyboard mapping in the code is somewhat odd.

Code Organization

There are three crates

• mos6502 - the CPU emulation
• pet - other hardware emulation plus some trait definitions for the hardware emulation
• bluepet - the actual emulator using the other crates - implements the traits from the pet crate to use the given hardware