PseudoGPIO is a C++ library that allows an application running on a computer to control and use GPIO pins of an Arduino (or similar) board connected through USB through an API similar to the Arduino/Wiring one.

PseudoGPIO is based on a simple protocol based on the exchange of single-byte packets through a serial port.

The protocol allows for 8 different commands, encoded in the 3 higher-order bits of the packet. The remaining bits shall be interpreted differently, according to the command being issued.

No reply from the target shall be expected for any command, except where indicated.

Commands that do not provide a reply shall be assumed to have been executed correctly.

This command checks if the target board is alive and interpreting commands correctly. It also allows to retrieve the protocol version implemented by the board. The reply shall be a single byte with the following format:

Currently, only version 1 of the protocol is defined.

This command sets the mode of a pseudopin. Mode shall be interpreted as follows:

• 0: Input
• 1: Output

This command requests the status of a digital pseudopin. The reply is a single byte, of which only the LSB shall be interpreted as follows:

• 0: Low Level
• 1: High Level

This command sets the level of a digital pseudopin. Level shall be interpreted as in the DigitalRead command, i.e.:

• 0: Low Level
• 1: High Level

All commands involving a pseudopin number expect an integer in the range 0-15, which is generally mapped to the correspondingly numbered physical pin on the target board, but there might be exceptions depending on the particular target.

• Arduino Uno/Nano and other ATmega328-based Arduinos: Pseudopins are mapped to the correspondingly numbered pins
  • Pins 0 and 1 are used by the serial port and thus are not available
  • Pins 14 and 15 do not exist
    • Thus pseudopins 0/1/14/15 have no meaning on these boards
• STM32F103xx-based boards, such as Blue Pill, Black Pill, etc: Pseudopins 0-15 are mapped to physical pins PA0-PA15, with the following exceptions:
  • PA11 and PA12 are used by the USB connection, thus pseudopins 11 and 12 are mapped to PB11 and PB12
    • Note that PB12 drives the onboard led on the Black Pill (with inverted logic)
  • PA13 and PA14 are only available through the SWD header on the Black Pill