References
==========

.. [RPF21a] *Raspberry Pi Foundation.* https://www.raspberrypi.org/

.. [RPF21b] *Raspberry Pi
            Pico*. https://www.raspberrypi.org/products/raspberry-pi-pico/

.. [Reuter21a] *RP2040 PIO Emulator.*
               https://github.com/soundpaint/rp2040pio