Low Power Application on PIC32CM LE00 Using MPLAB® Harmony v3 Peripheral Libraries: Step 2

Last modified by Microchip on 2023/11/15 17:44

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.

RTC box

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

RTC clock configuration

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 PIC32CM LE00 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.

RTC configuration options

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

  • RTCprescaler=1
  • FGCLK−RTC=1024Hz
  • FRTC−CNT=FGCLK−RTC=1024Hz
  • Tinterrupt−period=500∗10−3s

(1)CompareValue=Tinterrupt−period∗FRTC−CNT=500∗10−3∗1024=512(0x200)

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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 SERCOM5, or drag and drop, to add the SERCOM instance 5 to the project.

SERCOM 5 box

Select the SERCOM 5 peripheral library and configure it for the I²C protocol:

sercom_5_configuration_options.png

Configure I²C Pins

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

pin_settings_tool.png

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

SERCOM pins setup 1

Now, select the MCC Pin Table tab and then scroll down to the SERCOM5 module as shown:

  • Enable I²C data (I2C_SDA) on PB30 (pin #95)
  • Enable I²C clock (I2C_SCL) on PB31 (pin #96)

pin table SERCOM5 configuration

Go back to the Pin Settings table and customize the PB30 and PB31 pins names as listed:

  • Pin ID: PB30
    • Custom Name: I2C_SDA
  • Pin ID: PB31
    • Custom Name: I2C_SCL

SERCOM 5 pin settings

Verify I²C Clock

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

clock configuration

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

peripheral clock settings

Once the window is opened, scroll down to the SERCOM5_CORE peripheral and select GCLK1 (1 MHz) as the source clock to generate the peripheral clock frequency.

SERCOM 5 clock configuration

When a peripheral is added to the project, the peripheral clock is automatically fed by the GCLK1. However, you must configure the peripheral clocks according to your needs (power consumption, performance, …).

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.

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Configure USART Peripheral Library, USART Pins, and Verify 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.

SERCOM 3 box

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

stdio tool

Connect the SERCOM3 USART output to the STDIO USART input.

SERCOM 3 stdio linked

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

SERCOM 3 Config options

Note: In this lab, the SERCOM3 (as USART) interrupt is disabled as the application does not need a callback on USART transfer complete. A USART transmit buffer empty event triggers the DMA to transfer one byte of data from source (user buffer) to 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 tab by clicking Project Graph > Plugins > Pin Configuration.

pin settings tool

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

  • Enable USART Transmit (SERCOM3_TX) on PB20 (pin #68)
  • Enable USART Receive (SERCOM3_RX) on PB21 (pin #69)

pin table sercom3 configuration

Go back to the Pin Settings table and customize the PB20 and PB21 pins names as indicated:

  • Pin ID: PB20
    • Custom Name: SERCOM3_TX
  • Pin ID: PB21
    • Custom Name: SERCOM3_RX

SERCOM 3 pin settings

Verify USART Clock

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

clock configuration

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

peripheral clock settings

Once the window is opened, scroll down to the SERCOM3_CORE peripheral and select GCLK1 (1 MHz) as the source clock to generate the peripheral clock frequency.

SERCOM 3 clock configuration

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.

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Configure DMA Peripheral Library

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

DMA configuration

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

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