MQTT - HAT Brick

This is the description of the MQTT API bindings for the HAT Brick. General information and technical specifications for the HAT Brick are summarized in its hardware description.

An installation guide for the MQTT API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

Sleep

Download (example-sleep.txt)

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# Change XXYYZZ to the UID of your HAT Brick

setup:
    # Turn Raspberry Pi and Bricklets off in 2 seconds for 30 minutes with sleep indicator enabled
    publish '{"power_off_delay": 2, "power_off_duration": 1800, "raspberry_pi_off": true, "bricklets_off": true, "enable_sleep_indicator": true}' to tinkerforge/request/hat_brick/XXYYZZ/set_sleep_mode 

API

All published payloads to and from the MQTT bindings are in JSON format.

If an error occures, the bindings publish a JSON object containing the error message as member _ERROR. It is published on the corresponding response topic: .../response/... for .../request/... and .../callback/... for .../register/....

Basic Functions

request/hat_brick/<UID>/set_sleep_mode
Request:
  • power_off_delay – Type: int, Range: [0 to 232 - 1]
  • power_off_duration – Type: int, Range: [0 to 232 - 1]
  • raspberry_pi_off – Type: bool
  • bricklets_off – Type: bool
  • enable_sleep_indicator – Type: bool
Response:
  • no response

Sets the sleep mode.

Note

Calling this function will cut the Raspberry Pi's power after Power Off Delay seconds. You have to shut down the operating system yourself, e.g. by calling 'sudo shutdown -h now'.

Parameters:

  • Power Off Delay: Time in seconds before the RPi/Bricklets are powered off.
  • Power Off Duration: Duration in seconds that the RPi/Bricklets stay powered off.
  • Raspberry Pi Off: RPi is powered off if set to true.
  • Bricklets Off: Bricklets are powered off if set to true.
  • Enable Sleep Indicator: If set to true, the status LED will blink in a 1s interval during the whole power off duration. This will draw additional 0.3mA.

Example: To turn RPi and Bricklets off in 5 seconds for 10 minutes with sleep indicator enabled, call (5, 60*10, true, true, true).

This function can also be used to implement a watchdog. To do this you can write a program that calls this function once per second in a loop with (10, 2, true, false, false). If the RPi crashes or gets stuck the HAT will reset the RPi after 10 seconds.

request/hat_brick/<UID>/get_sleep_mode
Request:
  • empty payload
Response:
  • power_off_delay – Type: int, Range: [0 to 232 - 1]
  • power_off_duration – Type: int, Range: [0 to 232 - 1]
  • raspberry_pi_off – Type: bool
  • bricklets_off – Type: bool
  • enable_sleep_indicator – Type: bool

Returns the sleep mode settings as set by request/hat_brick/<UID>/set_sleep_mode.

request/hat_brick/<UID>/set_bricklet_power
Request:
  • bricklet_power – Type: bool
Response:
  • no response

Set to true/false to turn the power supply of the connected Bricklets on/off.

By default the Bricklets are on.

request/hat_brick/<UID>/get_bricklet_power
Request:
  • empty payload
Response:
  • bricklet_power – Type: bool

Returns the power status of the connected Bricklets as set by request/hat_brick/<UID>/set_bricklet_power.

request/hat_brick/<UID>/get_voltages
Request:
  • empty payload
Response:
  • voltage_usb – Type: int, Range: [0 to 216 - 1]
  • voltage_dc – Type: int, Range: [0 to 216 - 1]

Returns the USB supply voltage and the DC input supply voltage in mV.

There are three possible combinations:

  • Only USB connected: The USB supply voltage will be fed back to the DC input connector. You will read the USB voltage and a slightly lower voltage on the DC input.
  • Only DC input connected: The DC voltage will not be fed back to the USB connector. You will read the DC input voltage and the USB voltage will be 0.
  • USB and DC input connected: You will read both voltages. In this case the USB supply will be without load, but it will work as backup if you disconnect the DC input (or if the DC input voltage falls below the USB voltage).

Advanced Functions

request/hat_brick/<UID>/get_spitfp_error_count
Request:
  • empty payload
Response:
  • error_count_ack_checksum – Type: int, Range: [0 to 232 - 1]
  • error_count_message_checksum – Type: int, Range: [0 to 232 - 1]
  • error_count_frame – Type: int, Range: [0 to 232 - 1]
  • error_count_overflow – Type: int, Range: [0 to 232 - 1]

Returns the error count for the communication between Brick and Bricklet.

The errors are divided into

  • ACK checksum errors,
  • message checksum errors,
  • framing errors and
  • overflow errors.

The errors counts are for errors that occur on the Bricklet side. All Bricks have a similar function that returns the errors on the Brick side.

request/hat_brick/<UID>/set_bootloader_mode
Request:
  • mode – Type: int, Range: See symbols
Response:
  • status – Type: int, Range: See symbols

Sets the bootloader mode and returns the status after the requested mode change was instigated.

You can change from bootloader mode to firmware mode and vice versa. A change from bootloader mode to firmware mode will only take place if the entry function, device identifier and CRC are present and correct.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

The following symbols are available for this function:

For mode:

  • "Bootloader" = 0
  • "Firmware" = 1
  • "BootloaderWaitForReboot" = 2
  • "FirmwareWaitForReboot" = 3
  • "FirmwareWaitForEraseAndReboot" = 4

For status:

  • "OK" = 0
  • "InvalidMode" = 1
  • "NoChange" = 2
  • "EntryFunctionNotPresent" = 3
  • "DeviceIdentifierIncorrect" = 4
  • "CRCMismatch" = 5
request/hat_brick/<UID>/get_bootloader_mode
Request:
  • empty payload
Response:
  • mode – Type: int, Range: See symbols

Returns the current bootloader mode, see request/hat_brick/<UID>/set_bootloader_mode.

The following symbols are available for this function:

For mode:

  • "Bootloader" = 0
  • "Firmware" = 1
  • "BootloaderWaitForReboot" = 2
  • "FirmwareWaitForReboot" = 3
  • "FirmwareWaitForEraseAndReboot" = 4
request/hat_brick/<UID>/set_write_firmware_pointer
Request:
  • pointer – Type: int, Range: [0 to 232 - 1]
Response:
  • no response

Sets the firmware pointer for request/hat_brick/<UID>/write_firmware. The pointer has to be increased by chunks of size 64. The data is written to flash every 4 chunks (which equals to one page of size 256).

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

request/hat_brick/<UID>/write_firmware
Request:
  • data – Type: [int, ...], Length: 64, Range: [0 to 255]
Response:
  • status – Type: int, Range: [0 to 255]

Writes 64 Bytes of firmware at the position as written by request/hat_brick/<UID>/set_write_firmware_pointer before. The firmware is written to flash every 4 chunks.

You can only write firmware in bootloader mode.

This function is used by Brick Viewer during flashing. It should not be necessary to call it in a normal user program.

request/hat_brick/<UID>/set_status_led_config
Request:
  • config – Type: int, Range: See symbols
Response:
  • no response

Sets the status LED configuration. By default the LED shows communication traffic between Brick and Bricklet, it flickers once for every 10 received data packets.

You can also turn the LED permanently on/off or show a heartbeat.

If the Bricklet is in bootloader mode, the LED is will show heartbeat by default.

The following symbols are available for this function:

For config:

  • "Off" = 0
  • "On" = 1
  • "ShowHeartbeat" = 2
  • "ShowStatus" = 3
request/hat_brick/<UID>/get_status_led_config
Request:
  • empty payload
Response:
  • config – Type: int, Range: See symbols

Returns the configuration as set by request/hat_brick/<UID>/set_status_led_config

The following symbols are available for this function:

For config:

  • "Off" = 0
  • "On" = 1
  • "ShowHeartbeat" = 2
  • "ShowStatus" = 3
request/hat_brick/<UID>/get_chip_temperature
Request:
  • empty payload
Response:
  • temperature – Type: int, Range: [-215 to 215 - 1]

Returns the temperature in °C as measured inside the microcontroller. The value returned is not the ambient temperature!

The temperature is only proportional to the real temperature and it has bad accuracy. Practically it is only useful as an indicator for temperature changes.

request/hat_brick/<UID>/reset
Request:
  • empty payload
Response:
  • no response

Calling this function will reset the Bricklet. All configurations will be lost.

After a reset you have to create new device objects, calling functions on the existing ones will result in undefined behavior!

request/hat_brick/<UID>/write_uid
Request:
  • uid – Type: int, Range: [0 to 232 - 1]
Response:
  • no response

Writes a new UID into flash. If you want to set a new UID you have to decode the Base58 encoded UID string into an integer first.

We recommend that you use Brick Viewer to change the UID.

request/hat_brick/<UID>/read_uid
Request:
  • empty payload
Response:
  • uid – Type: int, Range: [0 to 232 - 1]

Returns the current UID as an integer. Encode as Base58 to get the usual string version.

request/hat_brick/<UID>/get_identity
Request:
  • empty payload
Response:
  • uid – Type: string, Length: up to 8
  • connected_uid – Type: string, Length: up to 8
  • position – Type: char
  • hardware_version – Type: [int, ...], Length: 3, Range: [0 to 255]
  • firmware_version – Type: [int, ...], Length: 3, Range: [0 to 255]
  • device_identifier – Type: int, Range: [0 to 216 - 1]
  • _display_name – Type: string

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here. If symbolic output is not disabled, the device identifier is mapped to the corresponding name in the format used in topics.

The display name contains the HAT's name in a human readable form.

Callback Configuration Functions

request/hat_brick/<UID>/set_voltages_callback_configuration
Request:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
  • value_has_to_change – Type: bool, Default: false
Response:
  • no response

The period is the period with which the register/hat_brick/<UID>/voltages callback is triggered periodically. A value of 0 turns the callback off.

If the value has to change-parameter is set to true, the callback is only triggered after the value has changed. If the value didn't change within the period, the callback is triggered immediately on change.

If it is set to false, the callback is continuously triggered with the period, independent of the value.

New in version 2.0.1 (Firmware).

request/hat_brick/<UID>/get_voltages_callback_configuration
Request:
  • empty payload
Response:
  • period – Type: int, Unit: 1 ms, Range: [0 to 232 - 1], Default: 0
  • value_has_to_change – Type: bool, Default: false

Returns the callback configuration as set by request/hat_brick/<UID>/set_voltages_callback_configuration.

New in version 2.0.1 (Firmware).

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the corresponding .../register/... topic and an optional suffix. This suffix can be used to deregister the callback later.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

register/hat_brick/<UID>/voltages
Register Request:
  • register – Type: bool
Callback Response:
  • voltage_usb – Type: int, Range: [0 to 216 - 1]
  • voltage_dc – Type: int, Range: [0 to 216 - 1]

A callback can be registered for this event by publishing to the .../register/hat_brick/<UID>/voltages[/<SUFFIX>] topic with the payload "true". An added callback can be removed by publishing to the same topic with the payload "false". To support multiple (de)registrations, e.g. for message filtering, an optional suffix can be used.

If the callback is triggered, a message with it's payload is published under the corresponding .../callback/hat_brick/<UID>/voltages[/<SUFFIX>] topic for each registered suffix.

This callback is triggered periodically according to the configuration set by request/hat_brick/<UID>/set_voltages_callback_configuration.

The callback payload members are the same as request/hat_brick/<UID>/get_voltages.

New in version 2.0.1 (Firmware).