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README.md

piolib

PIOlib/libPIO is a user-space API to the rp1-pio driver, which gives access to the PIO hardware of RP1. It takes the form of a clone of the PICO SDK PIO API, where most of the methods are implemented as RPC calls to RP1. This allows existing PIO code to be run without (much) alteration, but runs into problems when it relies on the PIO state machine and the support code being closely coupled.

Build Instructions

Install the prerequisites with sudo apt install build-essential cmake - you need at least version 3.10 of cmake. Run the following commands, either here or in the top-level directory to build and install everything:

  1. cmake . (or create a build subdirectory and run cmake ..)
  2. make

If ls -l /dev/pio0 reports that the file is not found, you may need to update your Pi 5 firmware to one with PIO support and make sure that you are running a suitably recent kernel. If ls -l /dev/pio0 reports that the file is owned by root and group root, you should add the following to /etc/udev/rules.d/99-com.rules:

SUBSYSTEM=="*-pio", GROUP="gpio", MODE="0660"

Make sure to reboot or run sudo udevadm control --reload-rules && sudo udevadm trigger in order to apply the new group ownership.

Examples

  • piotest: This is the normal WS2812 example LED PIO code, but using DMA to send the data. The optional parameter is the GPIO number to drive; the default is 2.
  • piopwm: The PWM example, unmodified except for dynamic SM allocation and a command line parameter to choose the GPIO. The optional parameter is the GPIO number to drive; the default is 4.
  • piows2812: The ws2812 example, unmodified except for dynamic SM allocation and a command line parameter to choose the GPIO. The optional parameter is the GPIO number to drive; the default is 2.
  • rp1sm: Show the state of the hardware for a particular SM. The parameter is the number of the state machine to inspect.
  • dpi_csync: Nick's DPI composite sync generator. More of an example than something usable - it may conflict with the DPI driver in interlaced modes. Many parameters; defaults to SDTV line rate.
  • quadenc: A decoder for quadrature-encoded signals, as generated by rotary encoders such as old mechanical mice. The optional parameter is the base GPIO number for an adjacent pair of input signals; the default is 10 (the other half of the pair being 11).

Known issues

  • Blocking operations block the whole RP1 firmware interface until they complete.