Receiving characters from a UART under MQX

dcooper — Mon, 16 Nov 2015 23:51:53 GMT

I am trying to implement a serial (UART) interface on a K60 under MQX. This seemed relatively straight forward, but am having no success.

I intend to have a task that that opens and receives characters on ittyx port.

I do not know how many characters will be received.

I want to read 4 characters when available (a header) and then read additional characters based on a length value included in the first 4 bytes read. It did not seem unreasonable to think the MQX serial drivers could support this kind of use case. Can someone point me to example code or offer insights as to how the driver works?

Questions:

Should I be using read() or fread(), I am not clear on the difference?

If in a while(1) loop I make a call to fread() and no characters are available, does this task give up the cpu allowing other tasks to run.

If, as an example, the chip has received 8 bytes and I do an fread() to read the first 4 bytes, can I then do another fread() for the remaining bytes, will I get the next 4 bytes?

Re: Receiving characters from a UART under MQX

DavidS — Fri, 20 Nov 2015 00:09:31 GMT

Hi David,

Yes you can do this.

With UART in interrupt mode it will buffer the inputs and code can go extract as many bytes at a time as you want. And then go back and get more.

If too many bytes are received before reading from the buffer, then the buffer will retain what it accumulated and drop the rest of the incoming characters. The buffer is configurable in size in the BSP file init_sci.c. It defaults to 64 bytes for the TX buffer and 64 bytes for the RX buffer.

UPDATE:

I created test code for the Tower TWR-K60D100M+TWR-SER using C:\Freescale\Freescale_MQX_4_2\mqx\examples\hello2 example.

The three key files are attached (user_config.h, twrk60d100m.h, hello.c).

Recompile the BSP/PSP and hello2 MQX application.

Run it and use terminal with 115200baud, 8-bit, 1-stop, no parity.

The default terminal output window will show below if you do not type any character as input:

Hello

- World

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