mfkiwl/pico-hx

PCB combining Raspberry Pi Pico and iCE40 FPGA

PicoHX

This is an FPGA board that combines an iCE40 HX FPGA with the Raspberry Pi Pico. The Pico can program the FPGA over USB using a script included in this repo and then interact with it using GPIO.

KiCad rendering

DVI Demo

Pictured is an included DVI demo. First, the RP2040 was programmed with the USB software which then exposes a USB programmer device to the host. Then, the FPGA configuration containing the DVI test pattern config was uploaded from the host to the RP2040, which then programmed the FPGA, which then displayed the test pattern on screen. This DVI PMOD was used.

Features

• iCE40 HX FPGA (TQFP144, 1k pinout assumed)
• 10 Pico GPIOs connected to FPGA
  • 2 are connected to GBIN inputs
• 4x PMODs in a 2x double-PMOD arrangement
• 8x user LEDs for FPGA
• 1x CDONE LED
• 2x users buttons for FPGA
• 1x user button for Pico
• RUN button for Pico
• Headers for Pico SWD and hardware UART
• Footprint for QSPI PSRAM or flash
• Micro SD card slot

Design

Programming

All iCE40 configuration pins are routed to the RP2040 GPIO so the details of how or when it is programmed are up to the software. The included software in this repo will make the Pico present itself is a USB device with these interfaces:

• Vendor programmer interface: This is how the user can program the iCE40 at any time over USB, using the included picoprog.py script.
• CDC UART: This UART is separate to the hardware UART that is available on the dedicated pin header. By default, stdout is sent to the CDC UART for convenience.

FPGA clock

The pico exposes one pin that can directly output a clock from one of its PLLs with an optional divider. In the demo software, the USB PLL (48MHz) is divided by 4 to output a 12MHz clock for the FPGA. On the FPGA side, the GBIN5 pin is used for clock input so that the SB_PLL40_2F_PAD can be used.

Power

There is only a 1.2v regulator on the board as the Pico provides a 3.3v output. The 2V5_VPP input is tied to 3.3v as the NVCM isn't used in this project.

PIO support

The 10 GPIOs connected to the FPGA and 4 GPIOs connected to the SD card slot are in consecutive order, so PIO can be used.

Demo

A demo that displays several test patterns controlled by BTN-A and blinks the LEDs in succession can be found in rtl/demo.

cd rtl/demo
make prog

Usage

Building Pico software

It's assumed that the pico-sdk is installed and the required environment variables are set.

cd software
mkdir build
cd build
cmake ..
make

The software can then be flashed using picotool for example. Default behaviour of the software is to immediately flash the iCE40 with an included bitstream that runs a counter with output to the 8 user LEDs.

Programming iCE40 bitstream

It's assumed that the OSS FPGA toolchain is installed which includes yosys and nextpnr-ice40.

After the Pico software is flashed, it's ready to program the iCE40 using a custom USB driver script. The script is written in Python3 and requires pyusb.

pip3 install pyusb

It can then be programmed with similar usage to iceprog. The programmer script is picoprog.py.

./picoprog.py bitstream.bit