µTasker Forum

µTasker Forum => NXP^TM M522XX, KINETIS and i.MX RT => Topic started by: kyork on August 29, 2008, 10:23:43 PM

Title: UART XON/XOFF
Post by: kyork on August 29, 2008, 10:23:43 PM

This may be a simple misunderstanding on my part.  When operating in XON/XOFF mode, should the driver pass those control bytes to the application when fnRead() is called?

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TTYTABLE tInterfaceParameters;       //table for passing information to driver
QUEUE_HANDLE serialPortId;

tInterfaceParameters.Channel = 1;  // serial 0, 1, 2, 3, 4, etc.
tInterfaceParameters.ucSpeed =  SERIAL_BAUD_57600; // baud rate
tInterfaceParameters.Rx_tx_sizes.RxQueueSize = RX_BUFFER_SIZE;       // input buffer size
tInterfaceParameters.Rx_tx_sizes.TxQueueSize = TX_BUFFER_SIZE; // outpu buffer size
tInterfaceParameters.Task_to_wake = 0;
tInterfaceParameters.usConfig = (CHAR_8 | NO_PARITY | USE_XON_OFF | ONE_STOP | NO_HANDSHAKE | CHAR_MODE);    

serialPortId = fnOpen(TYPE_TTY, FOR_I_O, &tInterfaceParameters);
if ( serialPortId != 0 )  // open or change the channel with defined configurations (initially inactive)
{
fnDriver( serialPortId, (RX_ON | TX_ON), 0 );        // enable RX & TX
}
And then later

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int count = fnRead(serialPortId, inBuffer, inBlockLen);

inBuffer will contain a 0x11, the XON byte.  Should this be the case?  Shouldn't the driver remove those control bytes? 

Title: Re: UART XON/XOFF
Post by: kyork on August 29, 2008, 11:48:46 PM

I don't know if the behavior is correct, but I changed:

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else if ((XON_CODE == ch) && (tx_ctl->ucState & TX_WAIT)) {
    tx_ctl->ucState &= ~TX_WAIT;                                 // unblock transmitter
    send_next_byte(Channel, tx_ctl);                             // restart transmission, if paused
    return;
}
to

Code: [Select]

else if(XON_CODE == ch) {           
    if (tx_ctl->ucState & TX_WAIT) {
        tx_ctl->ucState &= ~TX_WAIT;                                 // unblock transmitter
        send_next_byte(Channel, tx_ctl);                             // restart transmission, if paused           
    }
    return;
}
in fnSciRxByte() in Tty_drv.c and it fixed my issue.

Title: Re: UART XON/XOFF
Post by: mark on August 30, 2008, 12:12:11 AM

Hi

I believe your understand is correct. When the sequence XOFF, XON, XOFF, XON occurs it works correctly. If, however, XON is received when not expected (no XOFF before) I think that it is not correct to pass the character to the input buffer.

It seems sensible to improve this:

        else if (XON_CODE == ch) {                                       // {13}
            if (tx_ctl->ucState & TX_WAIT) {                             // if in XOFF state
                tx_ctl->ucState &= ~TX_WAIT;                             // unblock transmitter
                send_next_byte(Channel, tx_ctl);                         // restart transmission
            }
            return;
        }

This is slightly different from your fix since it doesn't call send_next_byte() if it was not in XOFF state. Probably calling this will not cause any real problem but this takes no risks.

Thanks!

Regards

Mark