Arm® TrustZone® Getting Started Application on SAM L11: Step 2

Step 2.1: Configure Secure Real-Time Clock (RTC) Peripheral Library

1

Under the bottom left Available Components tab, expand Peripherals > RTC.
Double click or drag and drop RTC to add the RTC Peripheral Library (PLIB) to the Project Graph.

rtc_adding.png

2

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

rtc_clock_setup.png

Note: On the SAM L11 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, 1 second, 2 seconds, and 4 seconds.

3

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

rtc_configuration_setup.png

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 (i.e., 0x200).

Step 2.2: Configure Secure I²C Peripheral Library and Secure I²C pins

1

Under the Available Components tab, expand Peripherals > SERCOM.

Double click on SERCOM1 to add the SERCOM instance 1 to the project.

sercom_selection.png

Select the SERCOM 1 Peripheral Library and configure it for the I²C protocol as shown.

sercom_setup.png

Note:

  • 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 specified 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 specified in the specification of the temperature sensor chip (AT30TSE758).

2

Open the Pin Configuration tab by clicking MHC > Tools > Pin Configuration.

open_pin_configuration.png

3

Select the MHC Pin Settings tab and sort the entries by Ports, as shown below.

sercom_pins_setup_1.png

Now, select the MHC Pin Settings tab and then scroll down to the SERCOM1 module as shown below.

  • Enable I²C Clock (I²C_SCL)(SERCOM_PAD1) on PA17 (Pin #18) as Secure mode.
  • Enable I²C Data (I²C_SDA)(SERCOM_PAD0) on PA16 (Pin #17) as Secure mode.
sercom_pins_setup_2.png

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

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

1

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

Double click on SERCOM0 to add the SERCOM instance 0 to the project.

sercom_selection_for_uart.png

Select the SERCOM0 Peripheral Library in the Project Graph and verify default SERCOM Operation Mode configuration is set as USART. Configure it as shown:

uart_sercom_setup.png

Verify the default baud rate is set to 115200 Hz.

Note:

  • SERCOM0 (as USART) interrupt is disabled because Direct Memory Access (DMA) will be used (configured in the following steps) to transfer application buffer to the USART TX register and also recieves data from USART RX register.
  • As per the "SAM L11 Xplained Pro Evaluation Kit" design, SERCOM0 PAD2 and SERCOM0 PAD3 are used for SERCOM0 (as USART) data transmission and receiption.
  • The application will use the SERCOM0 (as USART) PLIB for printing messages on the serial terminal and reads a character from serial terminal as a user request to read last five stored temperature values from EEPROM.

2

Select the Pin Settings tab and then scroll down to the SERCOM0 module.

  • Enable USART_TX (SERCOM_PAD2) on PA24 (Pin #23) as NonSecure Mode.
  • Enable USART_RX (SERCOM_PAD3) on PA25 (Pin #24) as NonSecure Mode.
uart_sercom_pins_setup.png

Step 2.4: Configure Non-Secure DMA Peripheral Library

1

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

open_dma_configuration.png

2

Click on the DMA Settings tab.

  • Configure DMA Channel 0 to transmit application buffer to the USART TX register. The DMA transfers one byte from the user buffer to USART transmit buffer on each trigger.
  • Configure DMA Channel 1 to receive the USART RX register data to application recieve buffer. The DMA transfers one byte from the USART receive buffer to user buffer on each trigger.

Based on the trigger source, the DMA channels 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 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 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 DMA channels and configure the DMA channels.

sercom0_tx_dma_setup.png
Figure 2.1: SERCOM0 USART Transmit DMA Channel Setup
sercom0_rx_dma_setup.png
Figure 2.2: SERCOM0 USART Receive DMA Channel Setup

Note:

  • 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.
  • USART receive timeout event triggers DMA to transfer one byte of data from source (USART Rx register) to destination (user buffer). When all the requested bytes are received, DMA PLIB notifies the application by calling the registered DMA callback event handler.



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