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Step 7.1: Build and Program the Application
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Cover the light sensor on the I/O Xplained Pro board by placing your hand over it (or another element to put the light sensor in a dark environment) to print the temperature and message on the terminal. You 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:
Step 7.2: Observe Current Consumption on Data Visualizer
The Data Visualizer is a program to process and visualize data. The 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.
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Once the Data Visualizer is connected to the SAM L21 EDBG, different interfaces will appear. Select the Power interface and click on the Start button to start measuring the power consumption of the device.
The Power Analysis window will appear on the Data Visualizer tool interface.
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The step image shows the device in Standby mode with its measured power consumption. You can observe small peaks that illustrate the 500 milliseconds Real-Time Clock (RTC) timer expiry.
The average value is considered when measuring the power consumption of the device because the instant value is not stable. Then, the power consumption of the device in Standby mode is 6.99 µA.
Note that the above results highlight the power consumption is lower in Standby mode than in Idle mode.
Step 7.3: 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.
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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, you can conclude that the wake-up time is greater in Standby mode than in Idle mode.
Results
You successfully created a low power application using the SAM L21 Xplained Pro Evaluation Kit and I/O1 Xplained Pro Kit and experienced how, where, and which Low Power mode to use depending on the application requirements such as power and wake up response times.
Analysis
In this lab, you have successfully created a project from scratch, added Peripheral Libraries (PLIBs) and learned how to use an Event System to drive events received from the peripherals without CPU intervention. You also learned how to configure a device to work in Sleep modes and measure wake up time.
Conclusions
In this tutorial, you discovered how to configure the device to work in Sleep modes, this tutorial can be used as a reference when you develop a real-time application where the power and wake up response time plays a crucial role.