Step 2.1: Configure RTC Peripheral Library
2
Verify that the RTC clock is set to run at 1 kHz using the 1 kHz Ultra Low Power Internal Oscillator (OSCULP1K).
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.
3
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
- $RTC_ {\rm prescaler} = 1$
- $F_{\rm GCLK-RTC} = 1024 Hz$
- $F_{\rm RTC-CNT} = F_{\rm GCLK-RTC} = 1024 Hz$
- $T_{\rm interrupt-period} = 500 * 10^{-3} s$
Step 2.2: Configure I²C Peripheral Library, I²C Pins, and Verify I²C Clock
Configure I²C Peripheral
Configure I²C Pins
Verify I²C Clock
3
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.
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, …).
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.
Step 2.3: Configure USART Peripheral Library, USART Pins, and Verify USART Clock
Configure USART Peripheral
4
Select the SERCOM 3 peripheral library in the Project Graph and configure it for USART protocol.
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
Verify USART Clock
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.
Step 2.4: Configure DMA Peripheral Library
2
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 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.
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