Step 2.1: Configure Real-Time Clock (RTC) Peripheral Library
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In Clock Easy View, verify 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).
On the SAM L10 device, the RTC can be clocked through several low power clock sources of 1 kHz and 32 kHz. The 1 kHz clock source retained (OSCULP1K) is enough to generate time periods of 500 milliseconds, 1 second, 2 seconds, and 4 seconds.
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Go back to the project graph and configure the RTC PLIB to generate a compare interrupt every 500 milliseconds.
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 (i.e., 0x200).
Step 2.2: Configure I²C Peripheral Library, I²C Pins, and Verify I²C Clock
1
Under the Device Resources tab, expand Harmpony > Peripherals > SERCOM.
Double-click on SERCOM1 to add the SERCOM instance 1 to the project.
Select the SERCOM 1 Peripheral Library and configure it for the I²C protocol.
- The SERCOM1 (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.
- The SERCOM1 (as I²C) retains the default 50-100 nanoseconds hold time for Serial Data (SDA) Hold Time because it aligns with the minimum (50 nanoseconds) start hold time in the specification of the temperature sensor chip (AT30TSE758).
- The SERCOM1 (as I²C) retains the default 100 nanoseconds for I2C Trise time because it aligns with the maximum (300 nanoseconds) input rise time in the specification of the temperature sensor chip (AT30TSE758).
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In Clock Easy View, open the Peripheral Clock Configuration by clicking on the button Peripheral Clock Configuration.
Once the window is opened, scroll down to the SERCOM1_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 Application Programming Interfaces (APIs) to read the temperature from the temperature sensor.
Step 2.3: Configure Universal Synchronous Asynchronous Receiver Transmitter (USART) Peripheral Library, USART Pins, and Verify USART Clock
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Under the tab Device Resources tab, expand Harmony > Peripherals > SERCOM.
Double-click on SERCOM0 to add the SERCOM instance 0 to the project.
Associate STDIO tool with SERCOM instance 0 (USART) peripheral by right clicking on the yellow diamond.
Select the SERCOM0 Peripheral Library in the Project Graph, verify default SERCOM Operation Mode configuration is set as USART and configure it.
Verify the default baud rate is set to 115200 Hz.
Note: In this lab, the SERCOM0 (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.
Step 2.4: Configure DMA Peripheral Library
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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 Serial Peripheral Interface (SPI) peripheral is configured for 16-bit/32-bit mode, then the beat size must be set to 16-bits/32-bits respectively.
Click on Add Channel to add the DMA channel and configure the DMA channel.
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, DMA PLIB notifies the application by calling the registered DMA callback event handler.
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