Computers and consoles using RBG video standard depends on the availability and cost of CRTs (Cathode Ray Tube) or LCD monitors that support low horizontal sync (15Khz) which are scarce or the use of converters that are expensive or produces deformation of the image and response time.

Open source options are either invasive or complex, requiring to open the computer or use layers of SBC (single board computers) and CPLDs / FPGAs 

With the appearance of the RP 2040 line of microcontrollers and the use of their capabilities, it was possible to consider a development that previously remained in the field of FPGA-based solutions such as OSSC or SCART converters, both of which have much higher final value and with limitations. in rendering fidelity (scaling) or in latency.

This project relies on the usage of the PIO (Programable IO) in order to delegate fast and cycle perfect processes that requires interaction with DMA and IRQs.

4 state machines are used, 3 for the TMDS and 1 for the ADC capture.

A detailed article about it plus some nostalgia: here in spanish

An article mention it: https://www.theregister.com/2024/03/02/hdmi_blocks_amd_foss/

Repository is NOW open: here on github

License: License is MIT without any additional disclaimer, just share your build and progress!

Features:

• HDMI modes: 640x480, 800x600, 960x540, 1280x720, all 60Hz
• Capture mode: 320x240 16 bit color, 640x240 8 bit color
• Simple USB drag and drop update
• Integration with companion app to control and capture images
• 3 key keyboard (previous, next, action) and a reset
• On Screen overlay menu system
• Max 24 bits color density, 18 bits on current HW

Tested on:

Commodore 128, Amiga 500, Amiga 1200, Atari ST 520, Sega Genesis

Use Mode

1.Connect retro computer through RGB video with its 2x5 , connectors can be provided

2.Power device through USB

3.Configure screen with buttons (alpha)

a.S2 Button : Alter between X and Y axis

b.S3 Button: Move left of up

c.S4 Button: Move right or down

d.Pushing S3+S3+S4: Activate USB

4.Console use:

a.Connect through USB with PC/Mac

b.Open a Serial port application (putty, arduino/monitor)

c.Configure 115000 8N1

d.Use comands with the following shape: <command> <space> <value> and hit enter

USB Commands

The USB commands allow you to speak directly with the microcontroller to command it, it is necessary (momentarily) to activate it by pressing the S2+S3+S4 buttons.

The USB mode affects the stability of the image, that is why it must be activated and is in test mode.

The list of commands may change in the future as needed, but at the moment the ones that are supported are:

• up: Move screen up, argument must be an integer (up 1)
• down: Move screen down, argument must be an integer (down 1)
• left: Move screen to the left, the argument must be an integer (left 1)
• right: Move screen to the right, the argument must be an integer (right 1)
• info: show info menu, argument must be true/false (info true)
• capture: capture the current screen in csv format. (capture)
• id: display the unique device id (id)
• version: show the version of the device (version)