The Pi Pico's PIO units should be able to be clocked to sync up to with the Mac and easily get accurate pixel samples without having to oversample. Some math would be involved to figure out how to divide the system clock (48MHz) down to the pixel clock and setting the PIO unit to run at that speed. So it could do something like:
The second PIO can run the VGA or DVI code to output the frame buffer. I'm not sure how do mix in an overlay but some of the examples might have a method of doing it. The main CPU cores can mine bitcoin or something while the PIOs do the hard work. Or maybe talk to an ESP32 for WiFi and the VNC server.
Oh, it probably needs a level shifter chip so the 5V video signals don't burn out the 3.3V inputs.
Code:
wait for hsync to drop
(maybe) wait out of front porch time
read 512 pixels and send them to the main CPU
- main CPU reads the pixels with DMA and dumps them into the frame buffer
repeat until vsync
loop
The second PIO can run the VGA or DVI code to output the frame buffer. I'm not sure how do mix in an overlay but some of the examples might have a method of doing it. The main CPU cores can mine bitcoin or something while the PIOs do the hard work. Or maybe talk to an ESP32 for WiFi and the VNC server.
Oh, it probably needs a level shifter chip so the 5V video signals don't burn out the 3.3V inputs.