Opening UART in registered Clock function throws Error

Michael Hoang

Other Parts Discussed in Thread: CC2650

Hello,

I'm trying to call UART_read() within a callbackFxn registered by Clock_construct(). Calling UART_read() completes the callback function, but then throws a "policySpin" error with the following code:

*
 *  ======== Pulse: registered with Clock_construct() =======
 */
Void Pulse(UArg arg0, UArg arg1)
{
	System_printf("Entering secondPulseFxn.\n");
	// For continuous runs, poll UART for STOP message
	unsigned char alertRx;
	if (continuousRun) {

		UART_read(uart, &alertRx, sizeof(alertRx));
		System_printf("Our alert: %i", alertRx);
}
}

// Somewhere else in code

    UART_Params_init(&uartParams);
    uartParams.readMode = UART_MODE_BLOCKING;
    uartParams.writeDataMode = UART_DATA_BINARY;
    uartParams.readDataMode = UART_DATA_BINARY;
    uartParams.readReturnMode = UART_RETURN_FULL; // Unblock when buffer is full
    uartParams.readEcho = UART_ECHO_OFF;
    uartParams.baudRate = 115200;
    uartParams.readTimeout = 10;
    uart = UART_open(Board_UART0, &uartParams);

If it helps, I'm using:

CCS Version: 6.1.3.00034

MCU: CC2650

TI-RTOS: 2.20

Not quick sure where to start with this one - commenting out UART_read() does not produce hanging of any kid. What's odd is the hanging only occurs after the callback is exited (i.e. I step though the last line of the callback). I've already enabled "BIOS.libType = BIOS.LibType_Debug;" in my .cfg script in an attempt for proper debug symbols to allow me to step through code with no such luck.

Ultimately, I'm trying to poll a UART handle periodically. I have several clock functions that are all time sensitive (micro-second granularity) and am trying to poll uart with the least amount of latency possible. This means avoiding for/while loops or using large receive buffers and this clock function is in charge of polling UART. If possible, I'd like to keep it within a Clock_construct() function as all of the clock functions are chained together. I've already tried closing my previous UART session and opening a UART session within this clock function without calling UART_read(). The same error is produced.

over 9 years ago

0 Michel Solecki over 9 years ago

Mastermind 8415 points

Hi Michael,

I see two problems:

You should not use a blocking call (your UART_read) from a Swi (you clock callback). It might take a long time and block other tasks.
The definition of the function pointer that you pass to clock construct takes only 1 argument Below is the definition of the function pointer that is expected:

typedef Void (*Clock_FuncPtr)(UArg);

I would recommend that you use polling from within a task. It will unblock after the "delay" and therefore offer a form of synchronism.

Alternatively, if you must use the clock to synchonize your tasks, you can use UART_MODE_CALLBACK (refer to documentation for more info). When using the callback mode, read only 1 character at a time. In your callback, you could store the character, and your clock callback would only check if any new characters have arrived.
Here is the pseudo code:

yourUARTcallback(....) {
  //fetch and store your character

  // Execute another non-blocking read
  UART_read(someTemporaryBuffer, 1);
}

yourClockCallback(....) {
  if (buffer is not empty(someTemporaryBuffer)) {
    // Execute some action here
  }
}

main(...) {
  // initialize and open your uart
  // construct your clock and pass the clock callback function

  BIOS_start();
}

Regards,

Michel

0 Kenia Guinto over 9 years ago in reply to Michel Solecki

TI__Expert 7250 points

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Opening UART in registered Clock function throws Error