pd-buddy-firmware/README.md

PD Buddy firmware

This is the firmware for the PD Buddy project. Currently, this specifically means the PD Buddy Sink. The firmware is currently under heavy development, but is largely functional.

Features

• 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.
• 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.
• Setup mode implements a USB CDC-ACM command-line interface allowing configuration to be loaded from and stored in flash.

Prerequisites

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. If you prefer to use SWD, you could also use stlink or OpenOCD.

Compiling

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}.

Flashing

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

dfu-util

Set the boot mode switch on the PD Buddy Sink to DFU mode and plug it into your computer. Flash the firmware with:

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

Don’t forget to set the switch back to normal mode after unplugging the device.

stlink

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

OpenOCD can also be used to flash the firmware. For example:

$ openocd -f interface/stlink-v2.cfg -f target/stm32f0x.cfg -c "program build/pd-buddy-firmware.elf verify reset exit"

Usage

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.

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.

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.