Can you display VGA and play audio on a Cortex-M4 in pure Rust? The short answer is yes, yes you can! Minus the hand-unrolled assembler loop for fixing the phase error in the RGB output. But we don't talk about that in polite company.

The rev 0.7 Monotron PCB is now here! I got five from JLCPCB.com to test out the idea. So far, I've shown that:

• The Atari Joystick interface works, but two Joysticks would be more fun
• The PS/2 Keyboard via the Atmega works, but the pinout was mirrored so you have to put the connector under the PCB :/
• The RTC works
• VGA Output works
• The MIDI Out seems to work when looped to MIDI In, as does the MIDI Though.
• The MIDI In seems to receive data when connected to my electronic drum kit
• The Audio output seems to work quite nicely
• The SD card works, but the power supply can't handle hot-insertion of the SD card and it makes the TM4C reboot. More capacitors / some current limiting probably required.

I can load games and programs from the SD card into the 24 KiB of free Application RAM. You can interact with these games via the PS/2 Keyboard and Joystick. I can play simple games (like Snake) and play three channels of 8-bit wavetable audio simultaneously. I've even got a 6502 Emulator running a copy of 6502 Enhanced BASIC, if you want to go old school!

The TODO list includes:

• Revising the PCB layout
  
  • Lose the 5V barrel jack - there's potential for problems if the USB is connected at the same time
  • Get the parallel port working
  • Add some mounting holes!
  • Add a second Joystick port
  • Add support for Sega Megadrive pads (which multiplex more than 8 signals on the 9 pin connector)
  • Find a way of leaving the Atmega reset as a reset pin, while still driving all 18 pins on the parallel port
  • Add an ICSP header for the Atmega
• Write a programming language!
  • It's call Monotronian (for now)
  • It allows line editing like BASIC
  • It parses / tokenises each line as entered and only stores tokens to save RAM
  • It can render tokens back to text when you LIST
  • It has fewer magic keywords (like BASIC's INPUT) and instead has more functions (like C or Python)
  • It has IF / ENDIF, WHILE / ENDWHILE, FN / ENDFN
  • Functions take named parameters
  • Scalar values are Integer, Float, String, and Char
  • Collections include Array and HashMap
  • APIs for Sound, Joystick, I/O, Text and Graphics
  • Can LOAD and SAVE like BASIC, but to SD card
  • PC version for testing / debugging
  • All written in pure Rust
• More games and demos!
  • Can we squeeze a MOD tracker into 24 KiB?
  • Use custom font as background tiles
  • Can we do a sprite as well as the text?
  • Write a MIDI synthesiser and/or sequencer you can plug a MIDI keyboard into
  • Write a MIDI player so you can play tunes on a Roland MT32 or similar
  • Write a text editor that can edit files much larger than RAM, using a swap-file on the SD card