Serial Stream connector - Amazon IoT Greengrass
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Amazon IoT Greengrass Version 1 no longer receives feature updates, and will receive only security patches and bug fixes until June 30, 2023. For more information, see the Amazon IoT Greengrass V1 maintenance policy. We strongly recommend that you migrate to Amazon IoT Greengrass Version 2, which adds significant new features and support for additional platforms.

Serial Stream connector

Warning

This connector has moved into the extended life phase, and Amazon IoT Greengrass won't release updates that provide features, enhancements to existing features, security patches, or bug fixes. For more information, see Amazon IoT Greengrass Version 1 maintenance policy.

The Serial Stream connector reads and writes to a serial port on an Amazon IoT Greengrass core device.

This connector supports two modes of operation:

  • Read-On-Demand. Receives read and write requests on MQTT topics and publishes the response of the read operation or the status of the write operation.

  • Polling-Read. Reads from the serial port at regular intervals. This mode also supports Read-On-Demand requests.

Note

Read requests are limited to a maximum read length of 63994 bytes. Write requests are limited to a maximum data length of 128000 bytes.

This connector has the following versions.

Version

ARN

3

arn:aws-cn:greengrass:region::/connectors/SerialStream/versions/3

2

arn:aws-cn:greengrass:region::/connectors/SerialStream/versions/2

1

arn:aws:greengrass:region::/connectors/SerialStream/versions/1

For information about version changes, see the Changelog.

Requirements

This connector has the following requirements:

Version 3
  • Amazon IoT Greengrass Core software v1.9.3 or later.

  • Python version 3.7 or 3.8 installed on the core device and added to the PATH environment variable.

    Note

    To use Python 3.8, run the following command to create a symbolic link from the the default Python 3.7 installation folder to the installed Python 3.8 binaries.

    sudo ln -s path-to-python-3.8/python3.8 /usr/bin/python3.7

    This configures your device to meet the Python requirement for Amazon IoT Greengrass.

  • A local device resource in the Greengrass group that points to the target serial port.

    Note

    Before you deploy this connector, we recommend that you set up the serial port and verify that you can read and write to it.

Versions 1 - 2
  • Amazon IoT Greengrass Core software v1.7 or later.

  • Python version 2.7 installed on the core device and added to the PATH environment variable.

  • A local device resource in the Greengrass group that points to the target serial port.

    Note

    Before you deploy this connector, we recommend that you set up the serial port and verify that you can read and write to it.

Connector Parameters

This connector provides the following parameters:

BaudRate

The baud rate of the serial connection.

Display name in the Amazon IoT console: Baud rate

Required: true

Type: string

Valid values: 110, 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 28800, 38400, 56000, 57600, 115200, 230400

Valid pattern: ^110$|^300$|^600$|^1200$|^2400$|^4800$|^9600$|^14400$|^19200$|^28800$|^38400$|^56000$|^57600$|^115200$|^230400$

Timeout

The timeout (in seconds) for a read operation.

Display name in the Amazon IoT console: Timeout

Required: true

Type: string

Valid values: 1 - 59

Valid pattern: ^([1-9]|[1-5][0-9])$

SerialPort

The absolute path to the physical serial port on the device. This is the source path that's specified for the local device resource.

Display name in the Amazon IoT console: Serial port

Required: true

Type: string

Valid pattern: [/a-zA-Z0-9_-]+

SerialPort-ResourceId

The ID of the local device resource that represents the physical serial port.

Note

This connector is granted read-write access to the resource.

Display name in the Amazon IoT console: Serial port resource

Required: true

Type: string

Valid pattern: [a-zA-Z0-9_-]+

PollingRead

Sets the read mode: Polling-Read or Read-On-Demand.

  • For Polling-Read mode, specify true. In this mode, the PollingInterval, PollingReadType, and PollingReadLength properties are required.

  • For Read-On-Demand mode, specify false. In this mode, the type and length values are specified in the read request.

Display name in the Amazon IoT console: Read mode

Required: true

Type: string

Valid values: true, false

Valid pattern: ^([Tt][Rr][Uu][Ee]|[Ff][Aa][Ll][Ss][Ee])$

PollingReadLength

The length of data (in bytes) to read in each polling read operation. This applies only when using Polling-Read mode.

Display name in the Amazon IoT console: Polling read length

Required: false. This property is required when PollingRead is true.

Type: string

Valid pattern: ^(|[1-9][0-9]{0,3}|[1-5][0-9]{4}|6[0-2][0-9]{3}|63[0-8][0-9]{2}|639[0-8][0-9]|6399[0-4])$

PollingReadInterval

The interval (in seconds) at which the polling read takes place. This applies only when using Polling-Read mode.

Display name in the Amazon IoT console: Polling read interval

Required: false. This property is required when PollingRead is true.

Type: string

Valid values: 1 - 999

Valid pattern: ^(|[1-9]|[1-9][0-9]|[1-9][0-9][0-9])$

PollingReadType

The type of data that the polling thread reads. This applies only when using Polling-Read mode.

Display name in the Amazon IoT console: Polling read type

Required: false. This property is required when PollingRead is true.

Type: string

Valid values: ascii, hex

Valid pattern: ^(|[Aa][Ss][Cc][Ii][Ii]|[Hh][Ee][Xx])$

RtsCts

Indicates whether to enable the RTS/CTS flow control. The default value is false. For more information, see RTS, CTS, and RTR.

Display name in the Amazon IoT console: RTS/CTS flow control

Required: false

Type: string

Valid values: true, false

Valid pattern: ^(|[Tt][Rr][Uu][Ee]|[Ff][Aa][Ll][Ss][Ee])$

XonXoff

Indicates whether to enable the software flow control. The default value is false. For more information, see Software flow control.

Display name in the Amazon IoT console: Software flow control

Required: false

Type: string

Valid values: true, false

Valid pattern: ^(|[Tt][Rr][Uu][Ee]|[Ff][Aa][Ll][Ss][Ee])$

Parity

The parity of the serial port. The default value is N. For more information, see Parity.

Display name in the Amazon IoT console: Serial port parity

Required: false

Type: string

Valid values: N, E, O, S, M

Valid pattern: ^(|[NEOSMneosm])$

Create Connector Example (Amazon CLI)

The following CLI command creates a ConnectorDefinition with an initial version that contains the Serial Stream connector. It configures the connector for Polling-Read mode.

aws greengrass create-connector-definition --name MyGreengrassConnectors --initial-version '{ "Connectors": [ { "Id": "MySerialStreamConnector", "ConnectorArn": "arn:aws-cn:greengrass:region::/connectors/SerialStream/versions/3", "Parameters": { "BaudRate" : "9600", "Timeout" : "25", "SerialPort" : "/dev/serial1", "SerialPort-ResourceId" : "my-serial-port-resource", "PollingRead" : "true", "PollingReadLength" : "30", "PollingReadInterval" : "30", "PollingReadType" : "hex" } } ] }'

In the Amazon IoT Greengrass console, you can add a connector from the group's Connectors page. For more information, see Getting started with Greengrass connectors (console).

Input data

This connector accepts read or write requests for serial ports on two MQTT topics. Input messages must be in JSON format.

  • Read requests on the serial/+/read/# topic.

  • Write requests on the serial/+/write/# topic.

To publish to these topics, replace the + wildcard with the core thing name and # wildcard with the path to the serial port. For example:

serial/core-thing-name/read/dev/serial-port
Topic filter: serial/+/read/#

Use this topic to send on-demand read requests to a serial pin. Read requests are limited to a maximum read length of 63994 bytes.

Message properties
readLength

The length of data to read from the serial port.

Required: true

Type: string

Valid pattern: ^[1-9][0-9]*$

type

The type of data to read.

Required: true

Type: string

Valid values: ascii, hex

Valid pattern: (?i)^(ascii|hex)$

id

An arbitrary ID for the request. This property is used to map an input request to an output response.

Required: false

Type: string

Valid pattern: .+

Example input
{ "readLength": "30", "type": "ascii", "id": "abc123" }
Topic filter: serial/+/write/#

Use this topic to send write requests to a serial pin. Write requests are limited to a maximum data length of 128000 bytes.

Message properties
data

The string to write to the serial port.

Required: true

Type: string

Valid pattern: ^[1-9][0-9]*$

type

The type of data to read.

Required: true

Type: string

Valid values: ascii, hex

Valid pattern: ^(ascii|hex|ASCII|HEX)$

id

An arbitrary ID for the request. This property is used to map an input request to an output response.

Required: false

Type: string

Valid pattern: .+

Example input: ASCII request
{ "data": "random serial data", "type": "ascii", "id": "abc123" }
Example input: hex request
{ "data": "base64 encoded data", "type": "hex", "id": "abc123" }

Output data

The connector publishes output data on two topics:

  • Status information from the connector on the serial/+/status/# topic.

  • Responses from read requests on the serial/+/read_response/# topic.

When publishing to this topic, the connector replaces the + wildcard with the core thing name and # wildcard with the path to the serial port. For example:

serial/core-thing-name/status/dev/serial-port
Topic filter: serial/+/status/#

Use this topic to listen for the status of read and write requests. If an id property is included it the request, it's returned in the response.

Example output: Success
{ "response": { "status": "success" }, "id": "abc123" }
Example output: Failure

A failure response includes an error_message property that describes the error or timeout encountered while performing the read or write operation.

{ "response": { "status": "fail", "error_message": "Could not write to port" }, "id": "abc123" }
Topic filter: serial/+/read_response/#

Use this topic to receive response data from a read operation. The response data is Base64 encoded if the type is hex.

Example output
{ "data": "output of serial read operation" "id": "abc123" }

Usage Example

Use the following high-level steps to set up an example Python 3.7 Lambda function that you can use to try out the connector.

Note
  1. Make sure you meet the requirements for the connector.

  2. Create and publish a Lambda function that sends input data to the connector.

    Save the example code as a PY file. Download and unzip the Amazon IoT Greengrass Core SDK for Python. Then, create a zip package that contains the PY file and the greengrasssdk folder at the root level. This zip package is the deployment package that you upload to Amazon Lambda.

    After you create the Python 3.7 Lambda function, publish a function version and create an alias.

  3. Configure your Greengrass group.

    1. Add the Lambda function by its alias (recommended). Configure the Lambda lifecycle as long-lived (or "Pinned": true in the CLI).

    2. Add the required local device resource and grant read/write access to the Lambda function.

    3. Add the connector to your group and configure its parameters.

    4. Add subscriptions to the group that allow the connector to receive input data and send output data on supported topic filters.

      • Set the Lambda function as the source, the connector as the target, and use a supported input topic filter.

      • Set the connector as the source, Amazon IoT Core as the target, and use a supported output topic filter. You use this subscription to view status messages in the Amazon IoT console.

  4. Deploy the group.

  5. In the Amazon IoT console, on the Test page, subscribe to the output data topic to view status messages from the connector. The example Lambda function is long-lived and starts sending messages immediately after the group is deployed.

    When you're finished testing, you can set the Lambda lifecycle to on-demand (or "Pinned": false in the CLI) and deploy the group. This stops the function from sending messages.

Example

The following example Lambda function sends an input message to the connector.

import greengrasssdk import json TOPIC_REQUEST = 'serial/CORE_THING_NAME/write/dev/serial1' # Creating a greengrass core sdk client iot_client = greengrasssdk.client('iot-data') def create_serial_stream_request(): request = { "data": "TEST", "type": "ascii", "id": "abc123" } return request def publish_basic_request(): iot_client.publish(payload=json.dumps(create_serial_stream_request()), topic=TOPIC_REQUEST) publish_basic_request() def lambda_handler(event, context): return

Licenses

The Serial Stream connector includes the following third-party software/licensing:

This connector is released under the Greengrass Core Software License Agreement.

Changelog

The following table describes the changes in each version of the connector.

Version

Changes

3

Upgraded the Lambda runtime to Python 3.7, which changes the runtime requirement.

2

Updated connector ARN for Amazon Web Services Region support.

1

Initial release.

A Greengrass group can contain only one version of the connector at a time. For information about upgrading a connector version, see Upgrading connector versions.

See also