Step 2.1: Configure RTC Peripheral Library
Verify that the RTC clock is set to run at 1 kHz internal ultra-low-power clock.
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 an internal 1 kHz ultra-low-power clock (OSCULP1K).
Note: On the SAM C21 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 (OSCULP1K) 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.
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
Select the Plugins > Pin Settings tab and sort the entries by Port names as shown below.
Now, select the Plugins > Pin Table tab and then scroll down to the SERCOM2 module as shown below.
- Enable I²C Clock (I2C SCL) on PA13 (Pin #30)
- Enable I²C Data ( I2C SDA) on PA12 (Pin #29)
Note: 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 and USART pins
Under the tab Device Resources tab, expand Harmony > Peripheral > SERCOM.
Double-click on SERCOM4 or drag and drop to add the SERCOM instance 4 to the project.
Select the SERCOM 4 peripheral library in the Project Graph and configure it for USART protocol.
Verify the default baud rate is set to 115200 Hz.
Note: The application will use the SERCOM4 (as USART) PLIB for printing messages on the serial terminal.
Step 2.4: Configure DMA Peripheral Library
Click on the DMA Settings tab. Configure DMA Channel 0 to transfer application buffer to the USART TX register. The DMA transfers one byte from the user buffer to 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-bits/32-bits respectively.