[GCP] Iot core

tl;dr

Terminology

referenced Technical overview of Internet of Things article.

• top-level components(3)

  • device: hardware itself and sw
  • gateway: connect to cloud services without internet
  • cloud: google cloud

• type of message

  • state information(data)
    • current status of the device
    • read/write
  • telemetry
    • device metric (i.g sensor data, gps …)
    • read only
    • Each source of telemetry results in a channel
    • Telemetry data might be preserved as a stateful variable on the device or in the cloud.

• commnads

  • actions performed by a device.
  • commands are often not idempotent
  • which means each duplicate message usually results in a different outcome

• operational information

  • i.g. CPU operating temperature and battery state
  • can be transmitted as telemetry or state data.

• serial interface

  • process of sending data one bit at a time, sequentially, over a communication channel or computer bus
  • contrast to parallel communication

• GPIO

  • General-purpose input/output pin
  • can be designed to carry digital or analog signals, and digital pins have only two states: HIGH or LOW.

• PWM

  • pulse width modulation
  • The effect in the device can be a lower or higher power level

• ADC

  • analog to digital conversion
  • analog -> binary

• I2C

  • Inter Integrated Circuit
  • Inter-Integrated Circuit serial bus uses a protocol that enables multiple modules to be assigned a discrete address on the bus
  • pronounced “I two C”, “I-I-C”, or “I squared C”.

• OTA update

  • over the air updates

GCP IoT Core conecpts

Devices, Configuration and State

1. Device metadata

metadata serves primarily as a label or identifier for devices. (or classifies devices)

• more secure than device state or device configuration because device metadata is never sent to or from a device
• shouldn’t change often (best: update it no more often than once per day)
• 500 key-value pairs (each key must be unique)
• Cloud IoT Core does not interpret or index device metadata
• e.g. hardware thumbprint, serial number, manufacturer information

2. Device configuration

IoT Core → device Sends desired state to robot with pre-defined commands like e.g.

• Device configuration is an arbitrary, user-defined blob of data sent from Cloud IoT Core to a device
• Device configuration is persisted in storage by Cloud IoT Core (64KB)
• After a configuration has been applied to a device, the device can report its state to Cloud IoT Core.
• A device configuration should focus on desired values or results, rather than on a sequence of commands
• Updates a device’s state by sending the expected state as a configuration
• Note that a device is not guaranteed to receive every configuration update
  • If a configuration is being updated rapidly, devices may not receive intermediate versions.

Configuration versions

• A device receives configurations only in increasing order of version numbers; in other words, it will never be sent a configuration older than its current version
• If the device reconnects to the MQTT bridge, it may receive an older configuration than it did during the earlier connection (rare case)

3. Device state

device → IoT Core Captures the current status of the device, not the environment

• Devices can describe their state with an arbitrary user-defined blob of data sent from the device to the cloud
• Device state information is not updated frequently.
• Configuration and state data can have the same schema and encoding, or they can be different
• e.g. health of the device or its firmware version