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Platform - UART Circular Buffer with LDMA

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Overview

This project uses an EFM32GG11 to receive UART frames into a circular buffer using LDMA.

Gecko SDK version

  • GSDK v4.4.3

Hardware Required

Connections Required

  • Connect the Giant Gecko GG11 Starter Kit to the CP2102N-EK USBXpress Bridge Development Kit via a micro-USB cable to your PC.
  • Connect the GG11 STK's PC1 pin to CP2102N-EK's TXD pin.

Setup

To test this application, you can either create a project based on an example project or start with an empty example project.

Create a project based on an example project

  1. Make sure that this repository is added to Preferences > Simplicity Studio > External Repos.

  2. From the Launcher Home, add the BRD2204A to My Products, click on it, and click on the EXAMPLE PROJECTS & DEMOS tab. Find the example project filtering by circular buffer.

  3. Click the Create button on the Platform - UART Circular Buffer with LDMA example. Example project creation dialog pops up -> click Finish and Project should be generated.

    Create_example

  4. Build and flash this example to the board.

Start with an empty example project

  1. Create an Empty C Project project for your hardware using Simplicity Studio 5.

  2. Replace the app.c file in the project root folder with the provided app.c (located in the src folder).

  3. Open the .slcp file. Select the SOFTWARE COMPONENTS tab and install the software components:

    • [Platform] → [Peripheral] → [LDMA]
    • [Platform] → [Peripheral] → [USART]

  4. Build and flash the project to your device.

How It Works

The application stays in EM1 until an interrupt occurs. After typing into Tera Term, the serial data from the USB is converted by the CP2102N into a UART signal that is stored into the GG11's USART RX FIFO. The LDMA is configured to start a transfer as soon as it sees data available in the FIFO. AFter the LDMA transfers BUFFER_SIZE/2 bytes of data to the circular buffer, the LDMA triggers an interrupt. In the interrupt handler, the application updates the stop index of the circular buffer to either 0 or BUFFER_SIZE/2. Set break points in interrupt handle function and start debugging to make sure that the application works correctly.

debug

In the case where less than BUFFER_SIZE/2 data bytes are received, the LDMA interrupt will not trigger. This presents an issue to the user: the circular buffer contains updated data, but the stop index is not updated. To fix this, the RX Timeout feature triggers an interrupt after 256 baud times if a new UART frame isn't received after a end of frame event. The interrupt handler updates the stop index according to the number of LDMA transfers that occured.