pio

Provides clean API to interact with RP2040's on-board Programable Input/Output (PIO) block. See chapter 3 of the RP2040 datasheet for more information.

piolib

This module contains the piolib package which contains importable drivers for use with a PIO such as:

• SPI driver
• 8-pin send-only parallel bus
• WS2812 (Neopixel) driver
• A pulse-constrained square wave generator (Pulsar)

Introduction to PIO

The PIO is a versatile hardware interface. It can support a variety of IO standards, including:

• 8080 and 6800 parallel bus
• I2C
• 3-pin I2S
• SDIO
• SPI, DSPI, QSPI
• UART
• DPI or VGA (via resistor DAC)

PIO is programmable in the same sense as a processor and has a total of nine instructions: JMP, WAIT, IN, OUT, PUSH, PULL, MOV, IRQ, and SET. These are programmed in PIO assembly format describing a PIO program, where each command corresponds to one instruction in the output binary. Below is an example program in PIO assembly:

.program squarewave
again:
    set pins, 1 [1] ; Drive pin high and then delay for one cycle
    set pins, 0     ; Drive pin low
    jmp again       ; Set PC to label `again`

How to install pioasm

To develop new code using PIO with this package, you must build and install the pioasm tool. It can be be built from the pico-sdk:

git clone git@github.com:raspberrypi/pico-sdk.git
cd pico-sdk/tools/pioasm
cmake .
make
sudo make install

How to develop a PIO program

To develop a PIO program you first start out with the .pio file. Let's look at the Pulsar example first.

1. pulsar.pio: specifies a binary PIO program that can be loaded to the PIO program memory.
2. all_generate.go: holds the code generation command on the line with //go:generate pioasm -o go pulsar.pio pulsar_pio.go which by itself generates the raw binary code that can be loaded onto the PIO along with helper code to load it correctly inside pulsar_pio.go.
3. pulsar_pio.go: contains the generated code by the pioasm tool.
4. pulsar.go: contains the User facing code that allows using the PIO as intended by the author.

Regenerating piolib

go generate ./...

Other notes

Keep in mind PIO programs are very finnicky, especially differentiating between SetOutPins and SetSetPins. The difference is subtle but it can be the difference between spending days debugging a silly conceptual mistake. Have fun!