framebuffers

Framebuffers

This folder accompanies the Project F blog post: Framebuffers. These SystemVerilog designs show you how to drive the display from a bitmap in memory. You can freely build on these MIT licensed designs. Have fun.

File layout:

• ice40 - designs for iCEBreaker and other Lattice iCE40 boards
• res - resources: bitmaps and palettes
• sim - simulation with Verilator and LibSDL; see the Simulation README
• xc7 - designs for Arty and other Xilinx 7 Series boards with VGA output
• xc7-dvi - designs for Nexys Video and other Xilinx 7 Series boards with DVI output

These designs make use of modules from the Project F library. Check the included iCE40 Makefile or Vivado create_project.tcl to see the list of modules used.

Demos

All based on an image of David by Michelangelo:

• David Mono - 160x120 dithered monochrome image
• David 16 Colour - 160x120 16-colour image
• David Scale - 160x120 16-colour image scaled to fill 640x480 display
• David Fizzle - Fizzle fade on scaled image of David

Learn more about the designs and demos from the Framebuffers blog post, or read on for build instructions. New to graphics development on FPGA? Check out Beginning FPGA Graphics.

David by Michelangelo generated by an Artix-7 FPGA using the david_scale demo.

iCEBreaker Build

You can build projects for iCEBreaker using the included Makefile with Yosys, nextpnr, and IceStorm Tools.

You can get pre-built tool binaries for Linux, Mac, and Windows from YosysHQ. If you want to build the tools yourself, check out Building iCE40 FPGA Toolchain on Linux.

For example, to build david_scale; clone the projf-explore git repo, then:

cd projf-explore/graphics/framebuffers/ice40
make david_scale

After the build completes, you'll have a bin file, such as david_scale.bin. Use the bin file to program your board:

iceprog david_scale.bin

If you get the error Can't find iCE FTDI USB device, try running iceprog with sudo.

Problems Building

If Yosys reports "syntax error, unexpected TOK_ENUM", then your version is too old to support Project F designs. Try building the latest version of Yosys from source (see above for links).

Arty Build

To create a Vivado project for the Digilent Arty (original or A7-35T); clone the projf-explore git repo, then start Vivado and run the following in the Tcl console:

cd projf-explore/graphics/framebuffers/xc7/vivado
source ./create_project.tcl

You can then build top_david_scale or top_david_fizzle etc. as you would for any Vivado project.

Simulation

This design includes a test bench for the XD and linebuffer modules. You can run the test bench simulation from the GUI under the "Flow" menu or from the Tcl console with:

launch_simulation
run all

Other Xilinx 7 Series Boards

It's straightforward to adapt the project for other Xilinx 7 Series boards:

1. Create a suitable constraints file named <board>.xdc within the xc7 directory
2. Make a note of your board's FPGA part, such as xc7a35ticsg324-1L
3. Set the board and part names in Tcl, then source the create project script:

set board_name <board>
set fpga_part <fpga-part>
cd projf-explore/graphics/framebuffers/xc7/vivado
source ./create_project.tcl

Replace <board> and <fpga-part> with the actual board and part names.

Nexys Video Build

To create a Vivado project for the Digilent Nexys Video; clone the projf-explore git repo, then start Vivado and run the following in the Tcl console:

cd projf-explore/graphics/framebuffers/xc7-dvi/vivado
source ./create_project.tcl

You can then build the designs as you would for any Vivado project.

Tested Versions

The Nexys Video designs have been tested with:

• Vivado 2022.2

Verilator SDL Simulation

You can simulate these designs on your computer using Verilator and SDL. The Simulation README has build instructions.

Linting

If you have Verilator installed, you can run the linting shell script lint.sh to check the designs. Learn more from Verilog Lint with Verilator.

SystemVerilog?

These designs use a little SystemVerilog to make Verilog more pleasant. See the Library README for details of SV features used.