3.14.1 Low Power Application on SAM L21 Xplained Pro Evaluation Kit

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Description

The application demonstrates low power application on SAM L21 Xplained Pro Evaluation Kit. on power-up, the device is set to Standby Sleep mode. The device wakes up from Standby mode and enters Active mode when the user covers the light sensor (by placing a hand over it, for example) on the I/O1 Xplained Pro extension kit. The application periodically prints room temperature on a serial terminal while the light sensor is covered. The device goes back to Standby mode when the user uncovers the light sensor. LED0 in the SAM L21 evaluation kit is toggled every time the temperature is displayed on the serial console. When the user presses the switch button SW0, the application switches Sleep mode from Standby mode to Idle mode.

Modules/Technology Used

  • Peripheral Modules:
    • I2C
    • RTC
    • USART
    • DMAC
    • ADC
    • PM
    • SUPC
    • EIC
    • EVSYS

Hardware Used

Note: The application is being developed on a SAM L21 XPRO-B board. Ensure that use the same revision on the evaluation board before going further, else the user could face issues with power consumption values.

Software/Tools Used

This project has been verified to work with the following versions of software tools:

Refer Project Manifest present in harmony-manifest-success.yml under the project folder firmware/src/config/sam_l21_xpro.

  • Refer the Release Notes to know the MPLAB X IDE and MCC Plugin version.
  • Any Serial Terminal application, such as Tera Term terminal application.

Because Microchip regularly updates tools, occasionally issue(s) could be discovered while using the newer versions of the tools. If the project does not seem to work and version incompatibility is suspected. It is recommended to double-check and use the same versions that the project was tested with. To download original version of MPLAB Harmony v3 packages, refer to document How to Use the MPLAB Harmony v3 Project Manifest Feature (DS90003305).

Setup

  • Connect the I/O1 Xplained Pro extension kit to the Extension Header 2 (EXT2) of the SAML21 Xplained Pro Evaluation Kit.
  • Probe PA02 (SW0 pin) and PB05 (wake-up test pin) on Extension Header 1 (EXT1) as highlighted in the Hardware Setup figure to measure wake-up time.
  • Connect a USB cable to the DEBUG USB port for programming.
    Note: Make sure common ground is connected with the board while using the logic analyzer or CRO.

Programming Hex File

The pre-built hex file can be programmed by following the below steps.

Steps to program the hex file:
  • Open MPLAB X IDE.
  • Close all existing projects in IDE, if any project is opened.
  • Go to File -> Import -> Hex/ELF File.
  • In the Import Image File window,
    1. Create Prebuilt Project,
      • Click the Browse button to select the prebuilt hex file.
      • Select Device as ATSAML21J18B.
      • Ensure the proper tool is selected under Hardware Tool and click on Next button.
    2. Select Project Name and Folder,
      • Select appropriate project name and folder and click on Finish button
  • In MPLAB X IDE, click on Make and Program Device button to program the device.
  • Follow the steps in Running the Demo section below.

Programming/Debugging Application Project

  • Open the project (saml21_low_power\firmware\sam_l21_xpro.X) in MPLAB X IDE.
  • Ensure SAML21 Xplained Pro (EDBG) is selected as hardware tool to program/debug the application.
  • Build the code and program the device by clicking on the Make and Program button in MPLAB X IDE tool bar.
  • Follow the steps in Make and Program Device section below.

Running the Demo

  • Open Tera Term, connect to serial console. If there is any connection issue on tera terminal, unplug the USB cable connected to Micro-B port, and reconnect it back.
  • Change the baud rate to 115200.
  • Perform a reset by pressing the RESET switch.
  • Verify the application title message is displayed.
  • Cover the light sensor on the I/O Xplained Pro board by placing the hand over it (or another element to put the light sensor in a dark environment) to print the temperature and message on the terminal. The user should see the following messages (containing the temperature value in °F) on the terminal every 500 milliseconds for the duration the light sensor is covered.
  • Observe Current Consumption on MPLAB Data Visualizer.
    Note: The MPLAB Data Visualizer is a program to process and visualize data. The MPLAB Data Visualizer can receive data from various sources, such as the Embedded Debugger Data Gateway Interface (EDBG DGI) and COM ports. It is possible to track an application in run-time using a terminal graph or oscilloscope. It analyzes the power consumption of an application through correlation of code execution and power consumption when used together with a supported probe or board.
  • Open the MPLAB Data Visualizer application from the MPLAB X IDE and select the connected SAM L21 Xplained Pro board on the Connectionstab, then enable the DGI.
  • Once the MPLAB Data Visualizer is connected to SAM L21 Xplained Pro, different interfaces will appear under the SAM L21 Xplained Pro. Select the Power interface and click on the Power Settings button. Then click on the ‘Calibrate’. After calibration is complete, click on the Start Capturing Power button. A window will pop up; select ‘Plot Raw’ and then click ‘Close’.
  • Note: Before calibrating the power, disconnect the Logic Analyzer from the SAML21 Xplained Pro Evaluation Kit, as it consumes power and may affect MCU power measurements.
  • Ensure that the jumpers for Current Measurement on the SAM L21 Xplained Pro are set to MEASURE for the MCU and BYPASS for the I/Os.
  • The Power Analysis window will appear on the MPLAB Data Visualizer tool interface.
  • The step image shows the device in Standby mode with its measured power consumption. The user can observe small peaks that illustrate the 500 milliseconds Real-Time Clock (RTC) timer expiry.
  • Cover the light sensor on the I/O Xplained Pro board by placing the hand over it (or another element) to print the temperature on the terminal and observe the power consumption of the device.
  • Press the SW0 button to switch from Standby mode to Idle mode. The following image shows the transition of the power consumption from Standby mode to Idle mode.
  • The following image shows the device in Idle mode with a measured power consumption of 373 µA.
    Note: The user can observe that the small peaks coming from RTC timer expiry disappeared because the power consumption in Idle mode is higher than the power required to start ADC conversion.
  • Place the hand over the light sensor. The device will wake up on the next ADC window monitor interrupt, read and print data on serial and then re-enter Standby mode. The following image shows the transition of the power consumption by switching from Idle mode to Standby mode.
    Note: The above results highlight the power consumption is lower in Standby mode than in Idle mode.
  • Wake-up Time Measurement Using Logic Analyzer/ Cathode-Ray Oscilloscope (CRO).

    To demonstrate the CPU wake up time, switch SW0 is configured to generate an interrupt. A General Purpose Input/Output (GPIO) is toggled in the Interrupt Service Routine (ISR) of the switch press event. The MCU comes out of Sleep mode when an interrupt occurs (in this case, the switch press interrupt). The time between the switch press and the GPIO toggle in the ISR is the wake up time.

  • Connect the logic analyzer or the CRO to the board according to the step image.
  • Press the SW0 switch and capture the signals to measure the wake-up time in Standby and Idle mode. The following image shows the wake-up time from Standby mode.
  • The following image shows the wake-up time from Idle mode.
  • By observing the outputs, the user can conclude that the wake-up time is greater in Standby mode than in Idle mode.

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