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open source bare-metal C firmware and documentation for microcontrollers


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MIT license

⚠️ Project name change notice

Apologies for any inconvenience caused. The Git project name has been shortened from "piconomix-fwlib" to "px-fwlib". Here is the Git command to change your cloned repo's URL:

git remote set-url origin

The online documentation URL has changed to:

PX-HER0 Board

STM32L072 PX-HER0 Board now in stock at Crowd Supply! Click HERE


px-fwlib is a collection of open source C firmware and documentation for microcontrollers to develop portable bare-metal code that is vendor and architecture neutral (or easier to reuse).

It is tough to find the best compromise between lean 8-bit targets, middle-of-the-road 16-bit targets, and resource rich 32-bit targets, but this cross-platform library aims to provide a good foundation before you are forced to add target specific code and getting locked in.

Click HERE to view the complete online documentation.

Click HERE to download releases of the open source library (source code and offline documentation).


  • Teach good firmware development practices to guide the next generation of professional embedded engineers.
  • Share source code, knowledge and expertise with our global community of engineers, scientists and enthusiasts.
  • Publish concise quick start guides and tutorials to reduce the learning curve of new microcontrollers.
  • Provide a standard framework and drivers for rapid code development.
  • Minimize porting by providing unified peripheral driver APIs (to maximize device driver reuse).

My sincere hope is that seasoned veterans will pitch in and share their years of experience to mentor the future generation and raise the bar in terms of quality and quantity.


Included with the library is a CLI (Command Line Interpreter) executing on an Arduino Uno R3 that creates an interactive shell environment so that you can experiment with GPIO, ADC, I2C and SPI using only an ANSI/VT100 terminal emulator (for example Tera Term).

Electrodragon BMP280 breakout board connected to I2C

Connect your board, fire up the CLI and verify that it works:

CLI Exlorer executing on an Arduino Uno R3

The BMP280 is found at 7-bit slave address 0x76. The chip identification register value for the BMP280 is 0x58. This confirms that you are able to write to and read from the I2C slave.

After verification, it is easy to accomplish the same in C using the library:

#include "px_i2c.h"
#include "px_board.h"

// Bosch BMP280 I2C Slave Address
#define I2C_SLA_ADR   0x76

// Create I2C Slave handle object
px_i2c_handle_t px_i2c_handle;

int main(void)
    uint8_t data[1];

    // Initialise board
    // Initialise I2C driver
    // Open handle to I2C slave device
    px_i2c_open(&px_i2c_handle, PX_I2C_NR_0, I2C_SLA_ADR);

    // START I2C write transaction and write register address
    data[0] = 0xd0;
    px_i2c_wr(&px_i2c_handle, data, 1, PX_I2C_FLAG_START_AND_END);
    // REPEATED START I2C read transaction and read register value
    px_i2c_rd(&px_i2c_handle, data, 1, PX_I2C_FLAG_REP_START_AND_STOP);

    // Close I2C Handle


MIT license

The MIT license has been selected to grant freedom for both open source and commercial (closed source) projects and to nurture future growth of the library. Please see the LICENSE.

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A significant amount of time has been invested to craft and refine this free open source library. If you saved development time, acquired a new skill, or advanced your career, you are welcome to support this project with a visit to the shop.

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