Problem with UART transmit

[RuPi_283656]

Hello. I am developing using Psoc 5. One of the things I need to do is repeatedly measure an A/D voltage and send the results over the serial RS232 line to a PC. Each transmission is 22 bytes and they are sent as fast as the processor can take an A/D reading.

   

Something strange is happening. It will send the value 276 times and then fail. The way it fails is that it starts a new transmission before the previous one has completed. It seems to be a buffer overflow problem but I have not found any method to correct the problem. However if I slow down the transmission frequency (for instance by taking each A/D reading 20 times and averaging) then the problem is not seen.

   

I started out using a TX buffer of 256 bytes. As a test I reduced TX buffer to 4 bytes, thinking that the problem might be in the interrupt routine. It made absolutely no difference. I am running RS232 ad 115 kBaud and I have added code to protect against buffer overflow (that code was disabled during the 4 byte tx buffer test). Each time I send the 22 byte data, I use the following code:

       

   SendSerial (buf, len);   // send 8 bytes
    SendSerial (((char*) &IRd, sizeof (ImRetData));  // send 22 bytes

   

The SendSerial routine looks like this:

   

Void SendSerial (char *buf, int len)
{
    WaitForUartTxBufEmpty (200);

   

    UART_PutArray ((BYTE*) buf, len);
}

   

void WaitForUartTxBufEmpty (int len)
{
    while (UART_GetTxBufferSize () > len);
}

   

Originally I had a timeout in the wait for empty routine, but removed it during testing to be sure it was not timing out. I have also tried changing the wait routine input length to zero.

   

I really think the problem is in the wait routine. I suspect that the routine returns before the buffer is empty, but debugging is difficult on this device. For instance it seems impossible to set debug conditions. If there is a way I would appreciate the info.

   

Thank you, Russ

[Bob_Marlowe]

UART_GetTxBufferSize() does return the number of USED bytes, not the number of free bytes, look at datasheet.

       

Bob

[RuPi_283656]

Hello Bob. Yes I agree with that, but that is what I am doing.  In routine

   

"WaitForUartTxBufEmpty". I am waiting for the number of used bytes to be reduced to zero, or some other value that will allow me to add the number of bytes required for the current operation.

   

I do think that "number of used bytes" means the number fo bytes in the buffer that are used, where used means "not yet sent".  The data sheel clearly states that "An empty buffer returns zero".

   

In reality I should not even have to use the Wait function to assure faithful transmission, as the data sheet states that UART_PutArray is a blocking function.  I added the wait test when I could not find a reason for the overwrite problem...

   

Thanks, Russ

[HeLi_263931]

Did you try to use the ReadTxStatus() for finding out whether the TX FIFO is empty or not?

[HeLi_263931]

And another question: are you sure the problem lies within the PSoC and not your receiving application? Maybe its just not fast enough?