PCFX Uploader

transmitting data from PC to a NEC PC-FX via microcontroller in GPL v3 licence.

Build

microcontroller_code contains the firmware in assembly for the LonganNano.
RP2040_device contains information on how to build an alternate microcontroller board, and firmware (C & PIO Assembly) for this board.
pc_code with the python script to upload data via UART connection.
pcfx_code contains the client on NEC PC-FX side in v810 assembly (make cd will build an CD bin/cue image).

To build just type make in the corresponding folder, or launch the script, given that you have the following tools in your path:
RV32 Assembler Bronzebeard
v810 binutils
pcfx-tools

The RP2040 device is based on pico-sdk version 1.4.0. To build, execute the command within 'build_xiao.sh', then 'cd build', and 'make'
pico-sdk

Summary

• the code on the PCFX side expects a magic word, start-address, execution-address and data length
• the code on the microcontroller mimics a PC-FX controller and sends all 32 keypad bits in the PC-FX specific protocol
• the code on the PC side simply connects to the microcontroller via UART
• The overall transmission speed is close to the UART limit despite a couple of extended wait loops on the PC-FX side. That could be optimized for speed if one really wanted to.

Setup

Longan Nano

This setup was used for initial development. The RP2040-based board will become the main supported plattform.
The Longan Nano is hooked up to Port2 of the PC-FX via 3V-5V level shifts (though it should be 5V tolerant)
It uses 5 lines: GND, VCC, CLOCK, LATCH and DATA.
The PC-FX pulls the LATCH line to low (0 Volts) when it wants more data to come in. Then it sends a quick clock signal HIGH,LOW,HIGH,...
The microcontroller senses that LATCH line, if it gets low, waits for it to get high then senses the CLOCK line and makes sure to put the proper signal on the output DATA depending on the state of your data bit (0 or 1). Initially, I tested that in C on the raspberry PI with some success. But it became clear that it would be too instable. Then I went for a microcontroller (with only ~100 Mhz) in C. That worked but I wasn't totally happy. Then I recoded the microcontroller in plain assembly (32bit RiscV, not too different from the PC-FX's native v810 CPU btw). The PC connects via UART to the native UART lines of the Longan Nano.

RP2040-based board

This operates the same as the Longan Nano, except observes the /OE line, which was found to control the direction of data on the DATA line (which means that data can flow both to and from the PC-FX). When this signal is high, the PC-FX sends data, so the microcontroller's output data line is tri-stated, and the signal is routed to an alternate pin to be used for inbound data. PIO assembly language is used for signal switching at high speeds, as this is its strength; the 'C' code merely acts as a traffic manager for the data. On this board, the USB port is used a virtual COM port, in order to keep the parts count to a minimum.

Demonstration

YouTube recording of initial LonganNano variant:

Credits

• PC-FX code and Longan board design and code: Martin 'enthusi' Wendt PriorArt
• RP2040 board design and code: David Shadoff

the folder pc_code contains the PC-FX binary mandelbrot from PC-FX Mandelbrot which you can use to send as an example python pysend.py mandelbrot.
See also: PriorArt website

Research

David Shadoff tested the signals from 'test data line release' based on a RP2040 setup with his logic analyzer and confirms our expectation, that the data line is indeed bidirectional. Also the OE signal change flags the used direction.