Harmony v3 Peripheral Libraries on SAM D5x/E5x: Step 2

Step 2.1: Configure RTC Peripheral Library


Under the bottom left Available Components tab, expand Peripherals > RTC.
Double click or drag and drop RTC to add the Real-Time Clock (RTC) Peripheral Library (PLIB) to the project graph.



Verify that the RTC is set to run at 1 kHz internal ultra-low-power clock.

When a module is added to the project graph, the MPLAB® Harmony Configurator (MHC) automatically enables the clock to the module. The default RTC source is an internal 1 kHz ultra-low-power clock (OSCULP1K).


Note: on the SAM E54 device, the 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 (OSCULP1K) is enough to generate time periods of 500 milliseconds, one second, two seconds, and four seconds.


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


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

  • RTC clock = 1024 Hz
  • RTC Prescaler = 1
  • Required Interrupt rate = 500 ms

Hence, Compare Value = (500/1000) x 1024 = 512 (0x200).

Step 2.2: Configure I²C Peripheral Library and I²C pins


Under the Available Components tab, expand Peripherals > SERCOM

Double click on SERCOM3 to add the SERCOM instance 3 to the project.


Select the SERCOM3 Peripheral Library and configure it for I²C protocol as shown.


Note: The SERCOM3 (as I²C) retains the default 100 kHz speed because the temperature sensor chip on I/O1 Xplained Pro Extension Kit can operate at 100 kHz I²C speed.


Open the Pin Configuratio tabs by clicking MHC > Tools > Pin Configuration.



Select the MHC Pin Settings tab and sort the entries by Port names as shown below.


Now, select the MHC Pin Table tab and then scroll down to the SERCOM3 module as shown below.

  • Enable I²C Clock (TWI_SCL) on PA22 (Pin #92)
  • Enable I²C Data (TWI_SDA) on PA23 (Pin #93)

Note: This completes the configuration of the I²C peripheral library. The application code will use the I²C PLIB Application Peripheral Interfaces (APIs) to read temperature from the temperature sensor.

Step 2.3: Configure Universal Synchronous Asynchronous Receiver Transmitter (USART) Peripheral Library and USART pins


Under the tab Available Components tab, expand Peripheral > SERCOM.

Double click on SERCOM2 to add the SERCOM instance 2 to the project.


Select the SERCOM2 Peripheral Library in the project graph and configure it for USART protocol as shown below.


Verify the default baud rate is set to 115200 Hz.

Note: the application will use the SERCOM2 (as USART) PLIB for printing messages on the serial terminal. Hence, only the transmit functionality is enabled and the receive functionality is disabled.


Select the Pin Table tab and then scroll down to the SERCOM2 module as shown below.

Enable USART_TX on PB25 (Pin #101).


Note: in the SERCOM2 (as USART) configuration, USART is enabled for TX functionality and no USART Rx functionality is enabled.

Step 2.4: Configure DMA Peripheral Library


Launch DMA Configurator by going to the MHC tab in MPLAB X IDE and then selecting Tools > DMA Configuration.



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

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

  • 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 Source/Destination Address after every transfer. Automatically set by the MHC, 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-bits/32-bits respectively.
  • Burst Length: this is a very fast data transfer mode. It can perform up to 16 transfers (beats) before releasing the control of the system bus back to the CPU. The default value of burst length is a single beat (one transfer).
    • In the default configuration, USART is configured for one-byte data at a time. So, the burst length is configured as a single beat.
  • FIFO Threshold: FIFO threshold level determines the size when the data in the internal DMA FIFO should be transferred to/from memory.
    • When the size of the data filled (in the internal DMA FIFO) becomes equal to the FIFO threshold size, the actual burst transfer (from the internal DMA buffer to USART peripheral) takes place, thereby improving the overall performance.
    • In the default configuration, the DMA transfers 1 beat of data as burst transfer.

Disable USART interrupt:


Under the Project Graph tab, click on the SERCOM2 block.


In the Configuration Options, uncheck the Enable Interrupts option.


Note: in this lab, SERCOM2 (as USART) interrupt is disabled as the application does not need a callback on USART transfer complete. A USART transmit buffer empty event triggers DMA to transfer one byte of data from source (user buffer) to destination (USART Tx register). When all the requested bytes are transmitted, DMA PLIB notifies the application by calling the registered DMA callback event handler.

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