PD Buddy Sink Firmware
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PD Buddy Sink Firmware

This is the firmware for the PD Buddy Sink, a smart power jack for USB Power Delivery.

The firmware is written using ChibiOS RT and HAL, and is comprised of a library for USB Power Delivery and an application using that library to request a configured voltage and current.


  • Two boot modes, Setup and Sink, selected by the Setup button’s state at startup.
  • Sink mode implements a simple USB Power Delivery sink, aiming for full compliance with the USB Power Delivery Specification, Revision 2.0, Version 1.3, and with Revision 3.0, Version 1.1.
  • Requests the configured voltage and current if available, or a safe, low power request otherwise.
  • Provides power on the output connector only when an explicit contract is in place for the configured voltage and current.
  • Optional GiveBack support allows power supplies to temporarily remove power from the PD Buddy Sink if necessary.
  • Requests can be made from programmable power supplies, allowing voltages to be requested at 20 mV increments from a wide range (up to 3-21 V).
  • Configuring a voltage range provides a fallback if the preferred voltage is unavailable.
  • The amount of current the device requests can be set as a power or a resistance, as well as a current. These values are taken as constant over the configured voltage range.
  • Setup mode implements a USB CDC-ACM command-line interface, compatible with Linux, Mac OS X, and Windows 10, allowing configuration to be loaded from and stored in flash.
  • Setup mode allows real-time renegotiation of voltage and current, complete with the ability to control whether the output is enabled or disabled.
  • Users can easily read a power supply’s advertised capabilities while in Setup mode using a PD Buddy Wye.
  • Firmware upgrades are easily possible via Setup mode in conjunction with the microcontroller’s built-in DfuSe bootloader.


To compile the firmware, you must first install the GNU ARM Embedded Toolchain. Details of its installation is beyond the scope of this README. Once the toolchain is installed, clone this repository with:

$ git clone --recursive http://git.clayhobbs.com/pd-buddy/pd-buddy-firmware.git

This will give you a complete copy of the repository, including the ChibiOS submodule.

You will also need to install some program to flash the firmware. The simplest option is dfu-util, as it requires no extra hardware (though if upgrading from versions older than 1.2.0, either the Boot switch must be installed or two pads must be bridged). If you prefer to use SWD, you could also use stlink, OpenOCD, or a Black Magic Probe.


With all the dependencies installed, the firmware can be compiled as follows:

$ cd pd-buddy-firmware
$ make

This compiles the firmware to build/pd-buddy-firmware.{bin,elf}.


The firmware can be flashed in any number of ways, including but not limited to the following:


To flash via DfuSe (ST Microelectronics’s extended version of the standard USB DFU protocol), the Sink must first be put into DFU mode. If upgrading from a version older than 1.2.0, or if no firmware is installed, set the Boot switch (SW1) on the PD Buddy Sink to the position not marked on the silkscreen to set the device to DFU mode. If your Sink doesn’t have a Boot switch installed, you can simply bridge the two pads of SW1 circled in this image with a blob of solder to achieve the same effect. Once this Sink is set to DFU mode, plug it into your computer.

If upgrading from firmware version 1.2.0 or later, you can easily enter DFU mode by running the following command from the Sink’s configuration shell:

PDBS) boot

This immediately puts the Sink in DFU mode until it is reset or unplugged.

When the Sink is in DFU mode, the Status LED should be glowing dimly. The firmware can then be flashed with:

$ dfu-util -a 0 -s 0x08000000:leave -D build/pd-buddy-firmware.bin

If this fails with a message like “dfu-util: Cannot open DFU device 0483:df11”, it’s likely that you don’t have permissions to write to the device. Try running dfu-util as root if this is the case.

If applicable, don’t forget to set the switch back to normal mode (or remove the solder blob) after unplugging the device.


If you have an ST-LINK/V2, you can use it to flash the firmware via SWD as follows:

$ st-flash write build/pd-buddy-firmware.bin 0x8000000


OpenOCD can also be used to flash the firmware. If your debug probe is an ST-LINK/V2, you can easily do this as follows:

$ make flash-openocd-stlink

Black Magic Probe

Black Magic Probe debuggers can be used to flash the firmware as well. This can be easily done as follows:

$ make flash-bmp


After first flashing the PD Buddy Sink, the device has no configuration. To configure it, plug it into your computer while holding the “Setup” button. The LED should blink once per second to indicate that the device is in configuration mode. There are then two ways to configure the Sink: a serial terminal, or the configuration GUI.

Configuration with the Serial Terminal

Connect to the PD Buddy Sink with your favorite serial console program, such as GNU Screen, Minicom, or PuTTY. Press Enter, and you should be greeted with a PDBS) prompt. The help command gives brief summaries of each of the available commands.

For example, to configure the PD Buddy Sink to request 2.25 A at 20 V, run the following commands:

PDBS) set_v 20000
PDBS) set_i 2250
PDBS) write

When write is run, the chosen settings are written to flash. You can then simply disconnect the Sink from your computer.

For more information about the serial console configuration interface, refer to the full documentation.

Configuration with the GUI

The Sink can also be configured by the PD Buddy Configuration GUI. For more information, see that repository’s README.

Using the configured PD Buddy Sink

Once the Sink has been configured, just plug it into your USB PD power supply. If the supply is capable of putting out the configured current at the configured voltage, the Sink will negotiate it, then turn on its output and blink the LED three times to indicate success. If the supply cannot output enough power, the Sink will turn its LED on solid to indicate failure, and leave its output turned off.

Status LED descriptions

LED State Mode Meaning
Fast blink (4 blink/sec) Sink Negotiating USB Power Delivery contract
Medium blink (2 blink/sec) Sink USB Power Delivery contract established, output on
Off Sink Output on
On Sink Unable to get configured power from source
Long blink (1 blink/2 sec) Sink Only default USB power is available (e.g. powered with USB A to C cable)
Slow blink (1 blink/sec) Setup Running in setup mode
Fast blink (4 blink/sec) Setup identify command run