This is a new effort to use an ICE40 device to implement a 100x37 text mode display (using 800x600 SVGA video with 8x16 characters) for an 8 bit microcomputer.
I learned a lot in my previous effort to do this, and I think I know the main things I did wrong in the previous effort. I also have an architecture in mind that (I think!) should be feasible to implement.
I make no guarantees regarding if or when this project might be complete enough to use. What I have now does output a correct video signal, and I'm happy with the way sync and timing are handled.
I'm using an Upduino 3.0 FGPA dev board with a resistor DAC which supports 4 bits of color signal for red/green/blue, so 4096 colors are possible. I'm using an external 10 MHz oscillator, which feeds a PLL generating a 40 MHz clock internally. (This is the exact dot clock we need for 800x600 SVGA.)
The Verilog code is built using Icestorm via the APIO front end.
To build and upload the design:
apio verify
apio build
apio upload
The circuit (note that the pushbutton is for generating a debounced reset signal):
Test display showing a grid (which demonstrates that the signal is putting the correct pixels in the correct rows and columns):
12/2/2023: Implemented a pixel buffer (pixbuf.v). This is a 1024x16 dual ported RAM (inferred as 4 256x16 block RAMs) from which pixel color values are read by the main pixel color output process. So, any pixel color values we put in here will be output to the display (assuming that they are put in at the appropriate time.) This seems to work! The pixel buffer is initialized with some 6x6x6 RGB color cube values, just so we have something to display, since no process is actually storing data to the pixel buffer yet.
11/28/2023: Made the github project public and added more information to the readme.
11/25/2023: Moved count, sync, and visibility signal generation to a separate module (timing_gen.v).
11/24/2023: Creation. Initial goal is to display a grid, with the goal of having the pixels drawn exactly correspond to hcount/vcount values. This does seem to be working!