RTOS/TM4C1294NCPDT: Unable to read all 8 UARTs in TI-RTOS without dropping data

Hello Todd,

It appears that the UARTs initialized earlier in order have less issues with data corruption. When I only setup 1 to 3 UARTs all the data is received correctly. This works when using any combination of UARTs (ex: 1/2/3 or 2/5/6). When I setup more than 3 or 4 UARTs then characters start being dropped. At 8 UARTs setup only the first 5 setup will receive data and the last few will receive very little to none (UARTs 1-2 a few missed, 3-5 multiple missing characters, 6-8 very few characters received).

I have also noticed when the tasks or callbacks run more code and take longer to execute that more data is dropped. After trying numerous methods I am currently trying to minimize the overhead of the read task and callback function. Not much difference (if any) is made when running the code in a project alone or with other tasks also running (ex: USB and Ethernet socket tasks).

Below is an example of how I am currently setting up the UARTs in a loop and reading/processing the data. Hopefully you have some magic formula that works like "use callbacks and queues with XYZ set to ___". I feel I'm close!

Thank you very much for your help!

#define UART_READ_TASK_STACK_SIZE        1024
#define MAX_NUM_RX_BYTES    8   // Maximum RX bytes to receive in one go

// Structs and Stacks used in read task creation below
Task_Struct uartReadTaskStruct[UART_COUNT];
Char uartReadTaskStack[UART_COUNT][UART_READ_TASK_STACK_SIZE];

// UART params are the same except for callback function
UART_Params      UARTParams;
UART_Params_init(&UARTParams);
UARTParams.baudRate  = UART_BAUD_RATE; // 19200
UARTParams.writeDataMode = UART_DATA_BINARY;
UARTParams.readEcho = UART_ECHO_OFF;
UARTParams.readMode = UART_MODE_CALLBACK; // sets up RX for callback mode
UARTParams.readTimeout = 0; // don't wait to receive


// Setup all UARTs and tasks to read them
for (uartLoop = 0; uartLoop < UART_COUNT; uartLoop++) {

        // Callback function adds the port number to read callback task args
        UARTParams.readCallback = UARTRxCallbackFuncs[uartLoop];
        UARTHandles[uartLoop] = UART_open(UARTsAvailable[uartLoop], &UARTParams);
        if (!UARTHandles[uartLoop]) {
            System_printf("UART%d did not open\n", uartLoop); // UARTs have always opened no issues
        }
        // Create tasks to periodically read UARTs
        taskParams.stackSize = UART_READ_TASK_STACK_SIZE;
        taskParams.priority = 3;
        taskParams.arg0 = uartLoop;
        taskParams.stack = &uartReadTaskStack[uartLoop];
        Task_construct(&uartReadTaskStruct[uartLoop], (Task_FuncPtr)UARTReadTask, &taskParams, NULL);
}

// Callback function
static void multipleByteReadCallback(UART_Handle handle, void *rxBuf, size_t size, uint8_t port)
{
    //Copy rxBuf to txBuf
    memset(UARTRxBufCopy[port], 0, MAX_NUM_RX_BYTES);
    memcpy(UARTRxBufCopy[port], rxBuf, size);
    Semaphore_post(readSemaphore[port]);
}

// Read function
static void UARTReadTask(UArg arg0, UArg arg1) {
    int port = (int) arg0;
    size_t charsReceivedSize;
    while (1) {
        UART_read(UARTHandles[port], UARTRxBuf[port], MAX_NUM_RX_BYTES);
        Semaphore_pend(readSemaphore[port], BIOS_WAIT_FOREVER);
        charsReceivedSize = strlen(UARTRxBufCopy[port]);
        // copy characters received to a partial data packet buffer
        // If end of data character is received, print data (or add to queue)
        Task_sleep(10); // Tried with and without sleep and various times, 5-25 appear to help
    }
}

HI Select user name please,

Have you configured M3 module or specific interrupt priorities for each UART? Does ROV indicate any kind of FIFO interrupt priority being assigned to each UART? How could we expect serial data would not be lost if the FIF0's are unconstrained or merely polled?

Hi User,

You could also try looking at the CPU load to see if you have the cycles to process the data from 8 UARTs at that baud rate.
Just add the following to your .cfg file:

xdc.useModule('ti.uia.sysbios.LoggingSetup');

Then use RTOS analyzer in CCS to look at the CPU load.

Best regards,

Janet

Hello Janet,

I am currently traveling and unable to test the system. In general should CPU load be an issue at all when simply reading 8 UARTs?

I understand that differences in code and settings may drastically change performance, but in general shouldn't the TM4C1294NCPDT have plenty of CPU to spare? Using an Arduino sketch I was able to get all 8 UARTs read perfectly and data stored in under 50 lines of code. We were also able to get it working with freeRTOS without any issues as well as run a full Ethernet web server.

Thank you.

Hi User,

Since you have one task per UART, I was wondering if there was a lot of overhead due to Task switching.  That's why I thought looking at the CPU load might be useful.

Best regards,

Janet

Hello Janet,

Thank you for the suggestion, having less tasks running made a big difference! I created a single read task and looped over each UART continuously. While looping over 6 UARTs about 90% of the characters are coming but it looks like from the data stream that the FIFO buffers are being overrun before being read.

The 10% being misses result in partial packets being mixed with full packets like: <123456<1234567890> instead of <1234567890><1234567890>. About 10 packets come in fine, then a mixed up one. No apparent pattern to which UART it will be.

The data is 64 characters sent every 4 seconds and the buffers are twice the size at 128 characters:

unsigned char uartTivaRingBuffer[EK_TM4C1294XL_UARTCOUNT][128];

/* UART configuration structure */
const UARTTiva_HWAttrs uartTivaHWAttrs[EK_TM4C1294XL_UARTCOUNT] = {
{
   .baseAddr = UART0_BASE,
   .intNum = INT_UART0,
   .intPriority = (~0),
   .flowControl = UART_FLOWCONTROL_NONE,
   .ringBufPtr  = uartTivaRingBuffer[EK_TM4C1294XL_UART0],
   .ringBufSize = sizeof(uartTivaRingBuffer[EK_TM4C1294XL_UART0])
},
{
   .baseAddr = UART1_BASE,
   .intNum = INT_UART1,
   .intPriority = (~0),
   .flowControl = UART_FLOWCONTROL_NONE,
   .ringBufPtr  = uartTivaRingBuffer[EK_TM4C1294XL_UART1],
   .ringBufSize = sizeof(uartTivaRingBuffer[EK_TM4C1294XL_UART1])
},...

I am using the following minimal code in a test project but still can't get the full data:

UART_Params      UARTParams;
UART_Params_init(&UARTParams);
UARTParams.baudRate  = UART_BAUD_RATE;
UARTParams.readReturnMode = UART_RETURN_NEWLINE;
UARTParams.readEcho = UART_ECHO_OFF;

static void UARTReadTask(UArg arg0, UArg arg1) {
    int port;
    int charsReceivedSize;
    uint8_t sizeLoop;
    char charReceived;
    while (1) {
        for (port = 0; port < UART_COUNT; port++) {
            if (!UARTsActivated[port]) {
                continue;
            }
            charsReceivedSize = UART_read(UARTHandles[port], UARTRxBuf[port], MAX_NUM_RX_BYTES);
            for (sizeLoop=0; sizeLoop<charsReceivedSize; sizeLoop++) {
                charReceived = ((char*)UARTRxBuf[port])[sizeLoop];
                dataPacketRxBuffer[port][dataPacketRxBufferIndex[port]] = charReceived;
                dataPacketRxBufferIndex[port] += 1;
                if (charReceived == '>') {
                    System_printf("UART%d received %s\n", port, dataPacketRxBuffer[port]);
                    System_flush();
                    dataPacketRxBufferIndex[port] = 0;
                }
            }
        }
    }
}

I tried getting the CPU logger working but couldn't get anything, even the Execution related items to work after looking at all the tips on the forums. I even tried with fresh examples from the Resource Explorer too and no luck. I guess I'm just used to using regular computers and Linux where things seem easier and to just work. These TI products seems to break at every opportunity.

I appreciate your help and especially any help with some simple code as this seems like it should be trivially easy.

Thank you.

I understand that TI-RTOS is much more complicated, but this is how easy it is with Arduino (how we prototyped on the TM4C1294NCPDT using Energia). TI just doesn't release the UART/USB/Ethernet drivers we needed to work with Arduino so we had to write it in C instead...

char termChart = '>';
char character;
int baudRate = 19200;

HardwareSerial *Serials[8] = {&Serial, &Serial1, &Serial2, &Serial3, &Serial4, &Serial5, &Serial6, &Serial7};
String rxStrings[8];

String completedRxString;
String storedRxString = "";

// Setup
void setup() {
  Serial.begin(baudRate);
  Serial.println("Serial test begin");
  for (int i = 0; i < 8; i++) {
    rxStrings[i] = "";
    Serials[i]->begin(baudRate);
  }
}

void loop() {
  for (int i = 0; i < 8; i++) {
    while(Serials[i]->available()) {
      character = Serials[i]->read();
      rxStrings[i].concat(character);
      if (character == termChart) {
//          Serial.print("Serial " + String(i) + ": ");
//          Serial.println(rxStrings[i]);
          completedRxString = String(i)+":"+rxStrings[i]+";";
          storedRxString.concat(completedRxString);
          rxStrings[i] = "";
      }
    }
    if (storedRxString.length() > 2000) {
      Serial.println(storedRxString);
      storedRxString = "";
    }
  }
}

Hi User,

I think you could do something similar to what is done in the Arduino code, using just one task to read the UARTs.  There is a UART_control() command which you can use to check whether or not data is available on the uart.  Here is how I modified the uartecho example to use the UART_control() call:

    int         dataAvailable;

    ...

    /* Loop forever echoing */
    while (1) {
        if ((UART_control(uart, UART_CMD_ISAVAILABLE, &dataAvailable) == UART_STATUS_SUCCESS) &&
                    (dataAvailable != 0)) {
            UART_read(uart, &input, 1);
            UART_write(uart, &input, 1);
        }
    }

There is also a UART_CMD_GETRXCOUNT control command that gives you the actual number of characters available to read.

Best regards,

Janet