Matter Sleepy End Devices over OpenThread

This page explains how Matter OpenThread Sleepy End devices (SEDs) work and how to configure an SED example.

Overview

Matter provides a Sleepy End Device (SED) operating mode to extend the battery life of a power-limited devices. This operating mode leverages OpenThread functionalities to enhance the provided Matter features. Matter Sleepy functionalities currently focus on allowing an application to define the interval of time where a device is asleep.

Operating Modes

SEDs have two operating modes, Idle and Active.

  • Active Mode sets the SED into a fast-polling interval for maximum responsiveness when the Node is engaged in ongoing communication, such as an active exchange. The SLEEPY_ACTIVE_INTERVAL parameter communicates the maximum sleep interval of a node in active mode.

  • Idle mode, or slow-polling, sets the maximum time an SED will sleep before polling. This parameter affects both the minimum power consumption and maximum latency. The SLEEPY_IDLE_INTERVAL parameter communicates the maximum sleep interval of a node in idle mode.

A device determines if it is in Active or Idle mode based on whether it has at least one open exchange in the message layer. As long as the device has one open exchanges, it will remain in Active mode and poll its associated OpenThread router at the fast-polling interval. Once all exchanges are closed, the device will switch operating modes to Idle Mode.

When a device is in Idle mode, it will poll its associated router at its slow-polling interval to see if another device has tried to communicate with it while it was sleeping. If the OpenThread router has an outstanding message for the SED, the SED will enter its Active polling mode to process the message.

Thread Communication

To receive message that were sent while the SED was sleeping, SED relies on its associated Thread router to buffer any incoming messages. The Thread router will send all buffered messages to the SED when the SED polls the router at the end of its slow-polling interval.

Configuration

Matter exposes three defines that can be set to configure the SLEEPY_ACTIVE_INTERVAL, SLEEPY_IDLE_INTERVAL and SLEEPY_ACTIVE_THRESHOLD parameters.

Parameter Name

Define

Description

Default Value

Maximum allowed Value

SLEEPY_IDLE_INTERVAL

CHIP_DEVICE_CONFIG_SED_IDLE_INTERVAL

Maximum node sleep interval when in idle mode.

30000 ms

<= 1 hour

SLEEPY_ACTIVE_INTERVAL

CHIP_DEVICE_CONFIG_SED_ACTIVE_INTERVAL

Maximum node sleep interval when in active mode.

200 ms

<= 1 hour

SLEEPY_ACTIVE_THRESHOLD

CHIP_DEVICE_CONFIG_SED_ACTIVE_THRESHOLD

Minimum amount the node SHOULD stay awake after network activity.

1000 ms

NA

Usage

The default values for the these defines for the Silabs platform are located in src/platform/silabs/CHIPDevicePlatformConfig.h.

/**
 * CHIP_DEVICE_CONFIG_SED_IDLE_INTERVAL
 *
 * The maximum amount of time in milliseconds that the sleepy end device will use as an idle interval.
 * This interval is used by the device to periodically wake up and poll the data in the idle mode.
 */
#ifndef CHIP_DEVICE_CONFIG_SED_IDLE_INTERVAL
#define CHIP_DEVICE_CONFIG_SED_IDLE_INTERVAL chip::System::Clock::Milliseconds32(SL_OT_IDLE_INTERVAL)
#endif // CHIP_DEVICE_CONFIG_SED_IDLE_INTERVAL

/**
 * CHIP_DEVICE_CONFIG_SED_ACTIVE_INTERVAL
 *
 * The minimum amount of time in milliseconds that the sleepy end device will use as an active interval.
 * This interval is used by the device to periodically wake up and poll the data in the active mode.
 */
#ifndef CHIP_DEVICE_CONFIG_SED_ACTIVE_INTERVAL
#define CHIP_DEVICE_CONFIG_SED_ACTIVE_INTERVAL chip::System::Clock::Milliseconds32(SL_OT_ACTIVE_INTERVAL)
#endif // CHIP_DEVICE_CONFIG_SED_ACTIVE_INTERVAL

/**
 * CHIP_DEVICE_CONFIG_SED_ACTIVE_THRESHOLD
 * 
 * The minimum amount of time Minimum amount the sleepy end device will stay awake after network activity.
 */
#ifndef CHIP_DEVICE_CONFIG_SED_ACTIVE_THRESHOLD
#define CHIP_DEVICE_CONFIG_SED_ACTIVE_THRESHOLD chip::System::Clock::Milliseconds32(SL_ACTIVE_MODE_THRESHOLD)
#endif // CHIP_DEVICE_CONFIG_SED_ACTIVE_THRESHOLD

The default values for the defines previously shown are located third_party/silabs/efr32_sdk.gni.

  # ICD Configuration flags
  sl_ot_idle_interval_ms = 30000  # 30s Idle Intervals
  sl_ot_active_interval_ms = 200  # 500ms Active Intervals
  sl_active_mode_threshold = 1000  # 1s Active mode threshold

There are two methods with which you can change these defaults values.

The first method is by adding these defines to CHIPProjectConfig.h file of your project. For the lighting-app, the file is examples/lighting-app/silabs/efr32/include/CHIPProjectConfig.h.

#define CHIP_DEVICE_CONFIG_SED_ACTIVE_THRESHOLD <value_ms>
#define CHIP_DEVICE_CONFIG_SED_ACTIVE_INTERVAL <value_ms>
#define CHIP_DEVICE_CONFIG_SED_ACTIVE_THRESHOLD <value_ms>

The second method is by adding arguments to the build command. Here is an example building the EFR32MG24 BRD4186C with different values.

./scripts/examples/gn_efr32_example.sh examples/lighting-app/silabs/efr32 out/lighting-app BRD41686C sl_ot_idle_interval_ms=1000 sl_ot_active_interval_ms=200 sl_active_mode_threshold=5000 --sed

If both methods of changing the default values are used, the defines added to the CHIPProjectConfig.h take precedence on the build arguments.

Building

Enabling Sleepy Functionalities

To build an OpenThread SED example, two conditions must be met: 1) The following macro must be defined : CHIP_DEVICE_CONFIG_ENABLE_SED and 2) the example must use the MTD OpenThread libraries to be able to leverage OpenThread Sleepy functionalities.

The --sed macro can be added to the build command to enable sleepy functionalities. Here is an example to build the light-switch-app as a SED for the EFR32MG24 BRD4186C.

./scripts/examples/gn_efr32_example.sh ./examples/light-switch-app/efr32/ ./out/light-switch-app_SED BRD4186C --sed

Minimal Power Consumption

Simply enabling Sleepy functionalities does not give the application the best power consumption. By default, several features that increase power consumption are enabled in the example applications. The following set of features increase power consumption.

  • Matter Shell

  • OpenThread CLI

  • LCD and Qr Code

To achieve the most power-efficient build, add these build arguments to the build command to disable all power-consuming features.

./scripts/examples/gn_efr32_example.sh ./examples/light-switch-app/efr32/ ./out/light-switch-app_SED BRD4186C --sed --low-power