breakintoprogram / pico-mposite

A hacked together demo for the Raspberry Pi Pico to output a composite video signal from the GPIO

Hi, I’m @breakintoprogram

I'm an ex-games developer who worked at various companies in the UK in the 80s and 90s

I now repair, code, and blog about retro computers as a hobby

You can find me on social media:

• Blog: breakintoprogram.co.uk
• Twitter: @breakintoprog
• YouTube: youtube.com/BreakIntoProgram
• Mastadon: oldbytes.space/@breakintoprogram
• Blue Sky: @breakintoprogram.bsky.social

I am quite happy contributing to the various communitiies I'm involved in with no obligations

However, if you like what I am doing and would like to contribute, you can do so at ko-fi.com/breakintoprogram

I am also raising money in memory of my good friend Geoff Follin in aid of Pancreatic Cancer UK

pico-mposite's Issues

Supporto for 60hz refresh

What can I modify to change the hscan to generate a proper 60Hz signal instead 50Hz?

Feature idea: YPbPr

Most recent TVs (here in the U.S., anyway) have at least one Component (YPbPr) video input.
Maybe the AD724 could be eliminated and the three DACs used to output Y, Pb, and Pr, directly. I believe "Y" is just RS-170 (grayscale) CVBS, and the other two are mathematically derived from the blue and red channels, respectively, of the original color image, but contain no sync information.
This is less of a request and more of a mention of the idea, in case anyone wants to work on it. I'd like to give it a try myself, someday, and this project is definitely a huge head-start toward that goal!

Support BBC-Micro Style TTL C-Sync, R, G, B

Thanks for an excellent project. I got a nice stable picture with the monochrome composite config at the first attempt.

Question: I am interested in making a simple pattern generator to test and debug Microvitec Cub monitors at the National Museum of Computing. That needs a signal that matches that from a BBC Micro, which is TTL level (1 bit) signals with Composite Sync, R, G, and B with PAL timing.

Looking at your work already it seems that should be fairly (!!) simple to add as a new colour option to the existing project. Is this something you would regard as potentially in-scope and be willing to collaborate on, or would you prefer if I worked on it solo?

One thing that isn't obvious to me from the code (and I haven't looked very hard) is the significance of all the bits in the 16 bit values you assign to identifiers like HSLO in cvideo.h. Can you explain what the bits do?

Bounds checking in draw_horizontal_line

draw_horizontal_line doesn't check its bounds correctly and can stamp over memory outside the bitmap.

The vertical position isn't checked before attempting to draw the line.

The horizontal position is clipped to max of width and should be clipped to width-1.

How to build?

The usual cmake .. from build doesn't work as expected. I spent some time trying to fixup the cmake file without any luck.

build$ cmake ..
CMake Warning (dev) in CMakeLists.txt:
  No project() command is present.  The top-level CMakeLists.txt file must
  contain a literal, direct call to the project() command.  Add a line of
  code such as

    project(ProjectName)

  near the top of the file, but after cmake_minimum_required().

  CMake is pretending there is a "project(Project)" command on the first
  line.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- The C compiler identification is GNU 10.3.0
-- The CXX compiler identification is GNU 10.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Error at CMakeLists.txt:3 (pico_generate_pio_header):
  Unknown CMake command "pico_generate_pio_header".


CMake Warning (dev) in CMakeLists.txt:
  No cmake_minimum_required command is present.  A line of code such as

    cmake_minimum_required(VERSION 3.18)

  should be added at the top of the file.  The version specified may be lower
  if you wish to support older CMake versions for this project.  For more
  information run "cmake --help-policy CMP0000".
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Configuring incomplete, errors occurred!
See also "/home/epoulsen/workspaces/pico-mposite/build/CMakeFiles/CMakeOutput.log".

External genlock

Amazing work.
How would you go to use this code with external sync, coming for example from a lm1881.
I guess one could configure interrupts per line and frame.

16bit per pixel support

I've been working on this vintage computer HDMI upscaler project for the Pi Zero:
https://github.com/IanSB/RGBtoHDMI/wiki

This takes up to 12 bpp digital inputs + sync and I was looking at sharpie7's test pattern generator fork of your project and it seems like it should be possible to modify your design for 16bpp support as I want to generate at least 12bpp digital test patterns for testing RGBtoHDMI boards.

Would it be possible to change this for 16bpp support and separate H & V syncs or are there any underlying bandwidth limitations etc?