PD Buddy Sink Firmware

PD Buddy Sink Serial Console Configuration Interface

Version 1.2.0-dev, 2017-12-09

The PD Buddy Sink can be put into setup mode by holding the Setup button while plugging it into a computer. In this mode, the device runs a configuration interface over a USB CDC-ACM virtual serial port in addition to the usual USB Power Delivery communications. This allows the user to change the voltage and current the Sink requests, as well as other settings related to the device’s operation.

Quick Start

Connecting to the Configuration Console

Connect to the PD Buddy Sink with your favorite serial console program, such as GNU Screen, Minicom, or PuTTY. On Linux, the device file will probably be something like /dev/ttyACM0. Any baud rate will work, as USB CDC-ACM doesn’t care what it’s set to. After connecting, press Enter and you should be greeted with a PDBS) prompt.

View the Saved Configuration

To see the configuration the device already has, run get_cfg:

PDBS) get_cfg
status: valid
flags: (none)
v: 9.00 V
i: 3.00 A

If the Sink has no configuration, this will simply print No configuration.

Setting Voltage and Current

The set_v and set_i commands allow you to set the voltage and current the Sink will request. The units used are millivolts and milliamperes. For example, to configure the device to request 2.25 A at 20 V, run the following commands:

PDBS) set_v 20000
PDBS) set_i 2250

Reviewing Configuration Changes

The changes made so far are held temporarily in RAM. To review the temporary configuration buffer, run get_tmpcfg:

PDBS) get_tmpcfg
status: valid
flags: (none)
v: 20.00 V
i: 2.25 A

Saving Configuration

The configuration buffer must be written to flash for the device to actually request the selected voltage and current. To do this, run:

PDBS) write

As soon as the prompt reappears after running write, the changes have been stored to flash, which can be verified with get_cfg. The Sink may be safely unplugged at any time.

Voltage Ranges

The preferred voltage may be set to any value for programmable power supplies. This means uncommon voltages may be set, e.g. 13.8 V. Few non-programmable power supplies offer such a voltage. To ensure a Sink configured this way can still work with as many power supplies as possible, it is possible to configure a closed range of acceptable voltages:

PDBS) set_v 13800
PDBS) set_vrange 11000 16000
PDBS) get_cfg
status: valid
flags: (none)
v: 13.80 V
vmin: 11.00 V
vmax: 16.00 V
i: 2.25 A

If 12 V and 15 V are available from a power supply, the Sink would request 12 V given this configuration. If higher voltages from the range are preferred over lower ones, it is possible to set this as well:

PDBS) toggle_hv_preferred
PDBS) get_cfg
status: valid
flags: HV_Preferred
v: 13.80 V
vmin: 11.00 V
vmax: 16.00 V
i: 2.25 A

To remove a configured voltage range, returning to a single desired voltage, simply set the top and bottom of the range to 0 V.

Alternate Configuration Types

While configuring a current to be requested at any voltage works well for some use cases (e.g. linear regulators), for others, it may make more sense to set the power required, or even the resistance of a resistive load. As of firmware version 1.2.0, the PD Buddy Sink supports setting these directly:

PDBS) set_p 45000
PDBS) get_tmpcfg
status: valid
flags: (none)
v: 20.00 V
p: 45.00 W
PDBS) set_r 8889
PDBS) get_tmpcfg
status: valid
flags: (none)
v: 20.00 V
r: 8.88 Ω

In either case, the device will set the current it requests according to the configured value. The value is kept constant across the entire configured voltage range, allowing the current to vary accordingly.

Commands

Commands are echoed on the terminal as characters are received. Lines are separated by \r\n and a command’s output ends with the PDBS) prompt. The character encoding used for text is UTF-8.

The command buffer can be cleared by sending ^D (a \x04 character). It is recommended to do this at the start of programmatic communications to ensure that the first command sent will be correctly processed.

If a received command is not recognized, the PD Buddy Sink responds with a line repeating the unknown command with any arguments removed, followed by a space and a question mark. For example:

PDBS) foo bar
foo ?

Miscellaneous

help

Usage: help

Prints short help messages about all available commands.

license

Usage: license

Prints licensing information for the firmware.

identify

Usage: identify

Blinks the LED quickly. Useful for identifying which device you’re connected to if several are plugged in to your computer at once.

Storage

get_cfg

Usage: get_cfg [index]

If no index is provided, prints the current configuration from flash. If there is no configuration, No configuration is printed instead.

For developers: if an index is provided, prints a particular location in the configuration flash sector. If the index lies outside the configuration flash sector, Invalid index is printed instead.

load

Usage: load

Loads the current configuration from flash into the buffer. Useful if you want to change some settings while leaving others alone. If there is no configuration, No configuration is printed instead.

write

Usage: write

Synchronously writes the contents of the configuration buffer to flash. Wear leveling is done to ensure long flash life, and the flash sector is automatically erased if necessary.

If the output is enabled, the newly written configuration is automatically negotiated. The newly configured power is then made available on the output connector if it is available from the source.

erase

Usage: erase

Synchronously erases all stored configuration from flash. This can be used to restore a device to its default state.

Note: The erase command is mainly intended for development and testing. Stored configuration is automatically erased if necessary when write is run, and wear leveling is performed as well. Unless you really know what you’re doing, there should be no reason to ever run erase.

Configuration

get_tmpcfg

Usage: get_tmpcfg

Prints the contents of the configuration buffer.

clear_flags

Usage: clear_flags

Clears the configuration buffer flags that can be toggled with toggle_* commands.

toggle_giveback

Usage: toggle_giveback

Toggles the GiveBack flag in the configuration buffer. GiveBack allows the power supply to temporarily remove power from the Sink’s output if another device needs more power. Recommended if the Sink is being used to charge a battery.

toggle_hv_preferred

Usage: toggle_hv_preferred

Toggles the HV_Preferred flag in the configuration buffer. When enabled, preference is given to higher voltages in the range. When disabled, preference is given to lower voltages.

set_v

Usage: set_v voltage_in_mV

Sets the voltage of the configuration buffer, in millivolts. Prints no output on success, an error message on failure.

Note: values are rounded down to the nearest 20 mV, 50 mV, or 100 mV for various parts of the USB Power Delivery protocol.

set_vrange

Usage: set_vrange min_voltage_in_mV max_voltage_in_mV

Sets the minimum and maximum voltage of the configuration buffer, in millivolts. Prints no message on success, an error message on failure.

Note: values are rounded down to the nearest 20 mV, 50 mV, or 100 mV for various parts of the USB Power Delivery protocol.

set_i

Usage: set_i current_in_mA

Sets the current of the configuration buffer, in milliamperes, overriding any power or resistance configured. Prints no output on success, an error message on failure.

Note: values are rounded down to the nearest 10 mA.

set_p

Usage: set_p power_in_mW

Sets the power of the configuration buffer, in milliwatts, overriding any current or resistance configured. Prints no output on success, an error message on failure.

Note: values are rounded down to the nearest 10 mW.

set_r

Usage: set_r resistance_in_mΩ

Sets the resistance of the configuration buffer, in milliohms, overriding any current or power configured. Prints no output on success, an error message on failure.

Note: values are rounded down to the nearest 10 mΩ.

Power Delivery

output

Usage: output [enable|disable]

If no argument is provided, prints the state of the power output (enabled or disabled).

If an argument is provided, sets the output to the specified state.

This command only affects whether the output can be turned on during the ongoing run of Setup mode. The output is disabled in Setup mode by default, and is always enabled in Sink mode.

get_source_cap

Usage: get_source_cap

Prints the capabilities advertised by the Power Delivery source. Each capability is represented by a Power Data Object (PDO), printed in the format listed in the PDO Format section below. If there are no capabilities, e.g. when the source does not support USB Power Delivery, No Source_Capabilities is printed instead.

Configuration Format

Wherever a configuration object is printed, the following format is used.

The configuration consists of a number of fields, one per line. Each field is of the format:

name: value

Only the status field is mandatory. Any or all other fields may be absent if their values are not valid or relevant.

status

The status field holds the name of the status of the printed configuration object. The possible names are:

empty: A configuration object left empty after the last erase.
valid: The configuration object that holds the current device settings.
invalid: A configuration object that once held settings, but has been superseded.

flags

The flags field holds zero or more flags. If no flags are enabled, the field’s value is (none). Otherwise, the field’s value is some combination of the following words, separated by spaces, representing the flags enabled in this configuration object:

GiveBack: allows the power supply to temporarily reduce power to the device if necessary.
HV_Preferred: precedence is given to higher voltages when selecting from the range (lower voltages take precedence when the flag is disabled).

v

The v field holds the preferred voltage of the configuration object, in volts. The field’s value is a floating-point decimal number, followed by a space and a capital V. For example: 20.00 V.

vmin

The vmin field holds the lower end of the configuration object’s voltage range, in volts. The field’s value is a floating-point decimal number, followed by a space and a capital V. For example: 20.00 V.

When absent, this field’s value may be assumed to be 0 V.

vmax

The vmax field holds the upper end of the configuration object’s voltage range, in volts. The field’s value is a floating-point decimal number, followed by a space and a capital V. For example: 20.00 V.

When absent, this field’s value may be assumed to be 0 V.

i

The i field holds the current of the configuration object, in amperes. The field’s value is a floating-point decimal number, followed by a space and a capital A. For example: 2.25 A.

p

The p field holds the power of the configuration object, in watts. The field’s value is a floating-point decimal number, followed by a space and a capital W. For example: 2.25 W.

r

The r field holds the resistance of the configuration object, in ohms. The field’s value is a floating-point decimal number, followed by a space and a capital Ω. For example: 2.25 Ω.

PDO Format

When a list of PDOs is printed, each PDO is numbered with a line as follows:

PDO n: type

n is the index of the PDO. type is one of fixed, typec_virtual, or the entire PDO represented as a 32-bit hexadecimal number if the type is unknown. If type is not a hexadecimal number, the rest of the PDO is printed as a list of fields, one per line, each indented by a single ASCII tab character. Each field is of the format:

name: value

Source Fixed Supply PDO Fields

This section describes how Source Fixed Supply PDOs (type fixed) are printed. For more information about the meaning of each field, see the USB Power Delivery Specification, Revision 2.0, Version 1.3, section 6.4.1.2.3.

dual_role_pwr

The dual_role_pwr field holds the value of the PDO’s Dual-Role Power bit (B29). If this field is not present, its value shall be assumed 0.

usb_suspend

The usb_suspend field holds the value of the PDO’s USB Suspend Supported bit (B28). If this field is not present, its value shall be assumed 0.

unconstrained_pwr

The unconstrained_pwr field holds the value of the PDO’s Unconstrained Power bit (B27). If this field is not present, its value shall be assumed 0.

usb_comms

The usb_comms field holds the value of the PDO’s USB Communications Capable bit (B26). If this field is not present, its value shall be assumed 0.

dual_role_data

The dual_role_data field holds the value of the PDO’s Dual-Role Data bit (B25). If this field is not present, its value shall be assumed 0.

peak_i

The peak_i field holds the value of the PDO’s Peak Current field (B21-20), in decimal. If this field is not present, its value shall be assumed 0.

v

The v field holds the value of the PDO’s Voltage field (B19-10), in volts. The field’s value is a floating-point decimal number, followed by a space and a capital V. For example: 20.00 V.

i

The i field holds the value of the PDO’s Maximum Current field (B9-0), in amperes. The field’s value is a floating-point decimal number, followed by a space and a capital A. For example: 2.25 A.

Type-C Current Virtual PDO Fields

This section describes how Type-C Current Virtual PDOs (type typec_virtual) are printed. These are not actually PDOs sent in a PD Source_Capabilities message, but merely a convenient way of reporting advertised Type-C Current when USB Power Delivery is not available.

i

The i field holds the value of the advertised Type-C Current, in amperes. The field’s value is a floating-point decimal number, followed by a space and a capital A. For example: 1.50 A.

USB Descriptors

The PD Buddy Sink can be identified by the following USB device descriptors:

idVendor: 0x1209 (InterBiometrics, or pid.codes)
idProduct: 0x9DB5 (PD Buddy Sink)

The device’s firmware version number is given in the iSerial descriptor. The version number follows Semantic Versioning. The serial console configuration interface is the API that the version number describes.

Starting with firmware version 1.2.0, the version number can also be read using the firmware version extension: an interface descriptor with class code 0xFF, subclass code 0x46, and protocol 0x57 points to a string descriptor with the firmware version.

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