Question

How can I extend the Bluetooth examples with UART functionality?

Answer

There are 3 options:

1. Use the standard printf and get functions which are retargeted to one USART or LEUART peripheral. 

This option is very easy to use but you cannot send binary data with this.

The easiest way to use printf is through the use of our retargetserial driver. To get started,

• copy the following files from the hardware\kit\common\drivers\ folder in the SDK to your project 
  • retargetio.c, retargetserial.h and retargetserial.c
• include retargetserial.h in your main.c
• call RETARGET_SerialInit() before the first call to printf()
• open hal-config.h and set the definition of HAL_VCOM_ENABLE  as shown below
  • #define HAL_VCOM_ENABLE                   (1)

Now you can call printf() anywhere in the application and the output will be directed through the virtual COMPORT. Please remember that printf() can take somewhat long to execute  so care should be taken in using it so that Bluetooth connections are not interrupted.

2. Use the em_usart or the em_leuart driver.

These drivers are part of the emlib. They provide an API for the USART and LEUART MCU peripherals.You can find more about the API here:

https://siliconlabs.github.io/Gecko_SDK_Doc/efr32bg1/html/group__USART.html

https://siliconlabs.github.io/Gecko_SDK_Doc/efr32bg1/html/group__LEUART.html

3. Use the uartdrv driver.

This driver is the most flexible from the available options. It is built on the top of emlib. The UART driver support both USART and LEUART peripherals.

The driver is fully reentrant and multiple driver instances can coexist. The driver does not buffer or queue data, but it queues UART transmit and receive operations. Both blocking and non-blocking transfer functions are available. Non-blocking transfer functions report transfer completion with callback functions. Transfers are done using DMA. Simple direct/forced transmit and receive functions are also available.

UART hardware flow control (CTS/RTS) is fully supported by the driver. UART software flow control (XON/XOFF) is partially supported. 

In this article we going to set up the uartdrv  to use the USART  peripheral in few steps. The attached example is demonstrating the initialization and the using of non-blocking RX/TX functions with implementing a simple echo functionality.

Setting up the uartdrv

Step 1 – Add the necessary emlib source files to the project from the gecko SDK. These are the followings:

platform\emlib\src\em_cmu.c

platform\emlib\src\em_core.c

platform\emlib\src\em_dma.c

platform\emlib\src\em_emu.c

platform\emlib\src\em_gpio.c

platform\emlib\src\em_int.c

platform\emlib\src\em_ldma.c

platform\emlib\src\em_leuart.c

platform\emlib\src\em_usart.c

Then add the necessary emdrv source files to the project from the gecko SDK. These are the followings:

platform\emdrv\dmadrv\src\dmadrv.c

platform\emdrv\gpiointerrupt\src\gpiointerrupt.c

platform\emdrv\uartdrv\src\uartdrv.c

Step 2 – Update the include paths of the project.

You need to add the emlib and emdrv include paths as listed below:

platform\emlib\inc

platform\emdrv\common\inc

platform\emdrv\dmadrv\config

platform\emdrv\dmadrv\inc

platform\emdrv\gpiointerrupt\inc

platform\emdrv\gpiointerrupt\inc

platform\emdrv\uartdrv\inc

platform\emdrv\uartdrv\config

In case using UART over J-Link CDC-on Silicon Labs boards you need the include path for the board and kit abstraction headers also. These headers containing the Virtual COM pin settings. The path for these are below:

hardware\kit\\common

hardware\kit\common\bsp

hardware\kit\common\halconfig

Step 3 – Once the necessary files and include paths are added you need to switch off the automatic sleeping feature of the Bluetooth stack. This is needed because the USART peripheral is not working in EM2.  It can be done by setting the gecko_configuration_t.sleep.flags to 0 as shown below.

/* Gecko configuration parameters (see gecko_configuration.h) */
static const gecko_configuration_t config = {
  .config_flags = 0,
  .sleep.flags = 0, // <- DISABLE THE SLEEP HERE
..
}