Skip to Content

Low Power Application on SAM L21 Using MPLAB® Harmony v3 Peripheral Libraries: Step 2

Last modified by Microchip on 2023/11/09 09:09

Configure RTC, I2C, USART, and DMA Peripheral Libraries

Configure RTC Peripheral Library

Click on the Resource Management [MCC] tab, In the Device Resources, expand Peripherals > RTC.
Double-click or drag and drop RTC to add the RTC peripheral library (PLIB) to the project graph.

Available Components and Project Graph pane

Verify that the RTC clock is set to run at 1 kHz using the 1 kHz Ultra Low Power Internal Oscillator (OSCULP1K).

RTC clock set to run at 1 kHz

Information

Note:

  • When a module is added to the project graph, MPLAB® Code Configurator (MCC) automatically enables the clock to the module. The default RTC clock source is OSCULP1K.
  • On the SAM L21 device, RTC can be clocked through several low-power clock sources of 1 kHz and 32 kHz as shown above. The 1 kHz clock source retained is enough to generate periods of 500 milliseconds.

 Go back to the project graph and configure the RTC PLIB to generate a compare interrupt every 500 milliseconds.

Configuration Options window

Information

Note: The Compare Value is set as 0x200. This compare value generates an RTC compare interrupt every 500 milliseconds.

  • RTCprescaler = 1
  • FGCLK−RTC = 1024 Hz
  • FRTC−CNT = FGCLK−RTC = 1024 Hz
  • Tinterrupt−period = 500 ∗ 10−3 s
    (1)
    CompareValue = Tinterrupt−period ∗ FRTC−CNT = 500 ∗ 10−3 ∗ 1024 = 512(0x200)

Back to Top

Configure I²C Peripheral Library, I²C Pins, and Verify I²C Clock

Configure I²C Peripheral

Click on the Resource Management [MCC] tab, In the Device Resources, expand Peripherals > SERCOM.
Double-click on SERCOM2 or drag and drop to add SERCOM instance 2 to the project.

Available Components and Project Graph pane

Select the SERCOM 2 peripheral library and configure it for the I²C protocol:

Configuration Options pane

Configure I²C Pins

Click Project Graph > Plugins > Pin Configuration to open the Pin Configuration tabs.

Tools > Pin Configuration menu

Once the MCC Pin Settings window is opened, find the Order drop-down list, and select Pins to sort the entries by port names.

Pin Settings window

Now, select the MCC Pin Table tab and then scroll down to the SERCOM2 module as shown:

  • Enable I²C data (I2C_SDA) on PA08 (pin #17)
  • Enable I²C clock (I2C_SCL) on PA09 (pin #18)

Pin Table

Go back to the Pin Settings table and customize the PA08 and PA09 pins names as listed:

  • Pin ID: PA08
    • Custom Name: I2C_SDA
  • Pin ID: PA09
    • Custom Name: I2C_SCL

Pin Settings pane

Verify I²C Clock

Open the Clock Configuration tab by clicking Project Graph > Plugins > Clock Configuration.

Tools > Clock Configuration menu

Open the Peripheral Clock Configuration tab by clicking on the button in the Peripheral Clock Selection.

Peripheral Clock Configuration tab​​

Once the window is opened, scroll down to the SERCOM2_CORE peripheral and select GCLK0 (12 MHz) as the source clock to generate the peripheral clock frequency.

Peripheral Clock Configuration pane​

Warning

When a peripheral is added to the project, the peripheral clock is automatically fed by the GCLK0. However, you must configure the peripheral clocks according to your needs (power consumption, performance, …).

Information

This completes the configuration of the I²C peripheral library. The application code will use the I²C PLIB APIs to read temperature from the temperature sensor.

Back to Top

Configure the USART Peripheral Library, and USART Pins, and Verify the USART Clock

Configure USART Peripheral

Under the left tab Resource Management (MCC), go to Device Resources and expand Libraries > Harmony > Peripherals > SERCOM.
Double-click on SERCOM3 or drag and drop to add SERCOM instance 3 to the project.

Available Components and Project Graph pane

Under the Resource Management (MCC) tab, go to Device Resources and expand Libraries > Harmony > Tools and double-click on STDIO or drag and drop to add the STDIO tool to the project.

Available Components and Project Graph pane

Connect the SERCOM3 USART output to the STDIO USART input.

SERCOM3 USART and STDIO USART​​

Select the SERCOM 3 peripheral library in the Project Graph and configure it for the USART protocol.

Configuration Options window​​

Information

Note: In this lab, the SERCOM3 (as USART) interrupt is disabled as the application does not need a callback on the USART transfer complete. A USART transmit buffer empty event triggers the DMA to transfer one byte of data from the source (user buffer) to the destination (USART Tx register). When all the requested bytes are transmitted, the DMA PLIB notifies the application by calling the registered DMA callback event handler.

Configure USART Pins

Open the Pin Configuration tabs by clicking Project Graph > Plugins > Pin Configuration.

Tools > Pin Configuration menu

Now, select the MCC Pin Table tab and then scroll down to the SERCOM3 module as listed below:

  • Enable USART Transmit (SERCOM3_TX) on PA22 (pin #43)
  • Enable USART Receive (SERCOM3_RX) on PA23 (pin #44)

Pin Table window

Go back to the Pin Settings table and customize the PA22 and PA23 pins names as indicated below:

  • Pin ID: PA22
    • Custom Name: SERCOM3_TX
  • Pin ID: PA23
    • Custom Name; SERCOM3_RX

Pin Settings window

Verify USART Clock

Open the Clock Configuration tab by clicking Project Graph > Plugins > Clock Configuration.

Tools > Clock Configuration menu

Open the Peripheral Clock Configuration tab by clicking on the button in the Peripheral Clock Selection.

Peripheral Clock Configuration tab

Once the window is opened, scroll down to the SERCOM3_CORE peripheral and select GCLK0 (12 MHz) as the source clock to generate the peripheral clock frequency.

Peripheral Clock Configuration pane

Information

This completes the configuration of the USART peripheral library. The application code will use the USART PLIB APIs to print messages on the serial terminal.

Back to Top

Configure DMA Peripheral Library

Open the DMA Configuration tabs by clicking Project Graph > Plugins > DMA Configuration.

Tools > DMA Configuration menu

Click on the DMA Settings tab. Configure DMA Channel 0 to transfer the application buffer to the USART TX register. The DMA transfers one byte from the user buffer to the USART transmit buffer on each trigger.

Based on the trigger source, the DMA channel configuration is automatically set by MCC.

  • Trigger Action: Action taken by DMA on receiving a trigger.
    • One beat transfer: Generally used during a memory-to-peripheral or peripheral-to-memory transfer.
    • One block transfer: Generally used during the memory-to-memory transfer on a software trigger.
  • Source Address Mode, Destination Address Mode: Select whether to increment the Source/Destination Address after every transfer. Automatically set by MCC based on the trigger type. For example:
    • If the trigger source is USART transmit, then the Source Address is incremented, and the Destination Address is fixed.
    • If the trigger source is USART receive, then the Source Address is fixed, and the Destination Address is incremented.
  • Beat Size: Size of one beat. The default value is 8 bits. For example:
    • If the SPI peripheral is configured for 16-bit/32-bit mode, then the beat size must be set to 16/32 bits respectively.
    • Enable Interrupts: In this Tab, SERCOM3 (as USART) Interrupt is enabled.

DMA settings window

Back to Top