Open-Source Firmware for ZY12PDN USB-PD

Open-source firmware for USB Power Delivery trigger board based on an FUSB302B power delivery controller and a STM32F030F4 MCU.

Building

• Clone the project from GitHub
• Open it with Visual Studio Code
• Install the PlatformIO extension
• Click the build icon in the status bar

Upload

The ZY12PDN board has a 4-pin SWD pads at the bottom. Either solder wires to them or use a 4-pin adapter with pogo pins.

Connect the SWD pads with an ST-Link, J-Link or Black Magic Probe to your computer and click the upload icon in the status bar of Visual Studio Code.

The boards initially have flash protection enabled. It can initially be disabled using openocd. Note: This command erase the flash memory:

openocd -f interface/stlink.cfg -f target/stm32f0x.cfg -c "init; reset halt; stm32f0x unlock 0; stm32f0x mass_erase 0; reset halt; exit

Hardware

See Hardware for a detailed description of the board and its components (incl. schematic).

Usage Instructions

The user interface – if it can be called so – is similar to the original ZY12PDN. The board can work in one of three modes:

• Interactive mode: By pressing the button, the board switches between available voltages.
• Fixed voltage mode: The board provides a configured voltage. If the configured voltage is not available, the board will output 5V.
• Configuration mode: By pressing the button, either the interactive mode or one of the fixed voltage modes is selected.

In all modes, the LED color indicates either the current voltage (interactive and fixed voltage mode) or the desired voltage (configuration mode).

Configuring the Board

The configuration mode is entered by plugging in the board while pressing the button. The LED will flash quickly in cyan until the button is released. The mode can be selected by pressing the button. To save the configuration, the button must be pressed for a longer period until the LED goes off. During configuration, the output voltage remains at 5V.

Supported PD Messages

• Capabilities: The source announces the supported voltages. The sink must immediately request one of the voltages.
• Request: The sink requests a specific voltage and maximum current.
• Accept: The source confirms the requested voltage. The new voltage is not ready yet.
• Reject: The source rejects the requested voltage.
• PS_RDY: The source indicates that the request voltage has been applied.

Notes

• If the event type of the pd_sink callback is callback_event::source_caps_changed, request_power() must be called to request a voltage -- even if it is 5V. Otherwise the source is likely to reset.
• The firmware is currently limited to the fixed voltages. Additionally capabilities (variable voltages etc.) can be easily added.
• Using the build flag -D PD_DEBUG, debugging output can be enabled. In order to see it, you have to solder a wire to PA2 (USART2 TX pin) and connect it to a serial adapter. The baud rate is 115,200 bps.
• The USB PD protocol is timing sensitive. Be very careful with debugging output in the source_caps_changed callback. It the debugging output takes too long, the USB power supply will likely reset and even cut the power.

Firmware Mode

The SWDIO line is shared with the interrupt line of the USB PD controller.

In order to enable firmware upload, the FUSB302B interrupt is not activated until USB PD activity has been detected. Instead, the code manually switches between measuring CC1 and CC2 even though the chip could do it automatically.

To upload firmware, connect a debug adapter (such as ST-Link or J-Link) to the SWD pads on the bottom of the board and provide power from any source except a USB PD power supply:

• Feed power to the USB connector from a non USB PD power supply
• Feed 3.3V to the VCC pad on the bottom side of the board (e.g. through an older ST-Link adapter)
• Feed 5V to the output terminal

SWD can be used to upload new firmware. But debugging is only possible until the interrupt pin is activated in code.

Acknowledgements

Thanks to the people that have also analyzed the ZY12PDN board and contributed to this work:

• Alex Whittemore: Notes on USB PD Triggers (and ZY12PDN Instructions) and ZY12PDN Reverse Engineering Part 1.
• Brian Lough: Powering your projects uing USB-C Power Delivery (YouTube)
• OxPeter and MarkOlsson on further people on Brian Lough's Discord Channel