PROCESSOR-SDK-AM64X: Bug in UART polling read

Simon Schwab

Tool/software:

Hi all,

I am using a UART instance configured in polling mode to read input from a terminal. I am using HTerm as terminal, not the integrated terminal of CCS.
I have a simple application where I read input with DebugP_readLine(pointer to buffer, 100u) and I can observe that UART_readPolling is in its read loop.

Now I send e.g. "foo" with a carriage return char via HTerm. I can see that the buffer is filled with my input but the application will hang forever in the polling read loop.

The problem is caused by a bug in uart_v0_lld.c (from MCU+ SDK v10.00.00.20) in the function UART_fifoRead:

1. While loop checks for 0 != readSizeRemaining
2. readSizeRemaining is never updated inside the loop, only tempReadSizeRemaining is. Therefore the loop will never break from this condition

Because I read input DebugP_readLine, readSizeRemaining will be 1 as it wants to read input character by character:

1. UART_fifoRead returns (size - tempReadSizeRemaining)
2. Because HTerm sends an input string altogether 4 characters have been read and the return value underflowed
3. UART_readPolling never returns although everything has been successfully read.

I guess the CCS terminal sends input after every keystroke unlike HTerm which never makes this bug visible.

7 months ago

0 Vaibhav Kumar 7 months ago

TI__Guru 50737 points

Hi,

Allow me sometime to check this on my setup. I will check the behaviour of the Polled reads and update you.

Regards,

Vaibhav

0 Vaibhav Kumar 7 months ago

TI__Guru 50737 points

Hi Simon,

I have observed that indeed this is a bug as the variable

readSizeRemaining is checked for but the variable

tempReadSizeRemaining should be checked for.

I have also noticed that the latest SDK release has this issue fixed.

static uint32_t UART_fifoRead(UARTLLD_Handle hUart, uint8_t *buffer,
                              uint32_t readSizeRemaining)
{
    uint32_t tempReadSizeRemaining = readSizeRemaining;
    uint32_t size    = tempReadSizeRemaining;
    Bool isRxReady = FALSE;
    uint8_t *tempBuffer = buffer;

    isRxReady = UART_statusIsDataReady(hUart);

    while (((Bool)TRUE == isRxReady) && (0U != readSizeRemaining))
    {
        /* once the H/w is ready  reading from the H/w                        */
        *tempBuffer = (UInt8) UART_readByte(hUart);
        tempBuffer++;
        --tempReadSizeRemaining;

        isRxReady = UART_statusIsDataReady(hUart);
    }

    return (size - tempReadSizeRemaining);
}

Marking the thread closed.

Regards,

Vaibhav

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PROCESSOR-SDK-AM64X: Bug in UART polling read