ttyhandle_out.c

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/* ttyhandle_out.c - ttyhandle_out */

#include <xinu.h>

/*------------------------------------------------------------------------
 *  ttyhandle_out  -  Handle an output on a tty device by sending more
 *           characters to the device FIFO (interrupts disabled)
 *------------------------------------------------------------------------
 */
void    ttyhandle_out(
     struct ttycblk *typtr,     /* Ptr to ttytab entry      */
     struct uart_csreg *csrptr  /* Address of UART's CSRs   */
    )
{
    
    int32   ochars;         /* Number of output chars sent  */
                    /*   to the UART        */
    int32   avail;          /* Available chars in output buf*/
    int32   uspace;         /* Space left in onboard UART   */
                    /*   output FIFO        */
    uint32  ier = 0;

    /* If output is currently held, simply ignore the call */

    if (typtr->tyoheld) {
        return;
    }

    /* If echo and output queues empty, turn off interrupts */

    if ( (typtr->tyehead == typtr->tyetail) &&
         (semcount(typtr->tyosem) >= TY_OBUFLEN) ) {
        ier = csrptr->ier;
        csrptr->ier = ier & ~UART_IER_ETBEI;
        return;
    }
    
    /* Initialize uspace to the available space in the Tx FIFO */

    uspace = UART_FIFO_SIZE - csrptr->txfifo_lvl;

    /* While onboard FIFO is not full and the echo queue is */
    /*   nonempty, xmit chars from the echo queue       */

    while ( (uspace>0) &&  typtr->tyehead != typtr->tyetail) {
        csrptr->buffer = *typtr->tyehead++;
        if (typtr->tyehead >= &typtr->tyebuff[TY_EBUFLEN]) {
            typtr->tyehead = typtr->tyebuff;
        }
        uspace--;
    }

    /* While onboard FIFO is not full and the output queue is   */
    /*   nonempty, transmit chars from the output queue     */

    ochars = 0;
    avail = TY_OBUFLEN - semcount(typtr->tyosem);
    while ( (uspace>0) &&  (avail > 0) ) {
        csrptr->buffer = *typtr->tyohead++;
        if (typtr->tyohead >= &typtr->tyobuff[TY_OBUFLEN]) {
            typtr->tyohead = typtr->tyobuff;
        }
        avail--;
        uspace--;
        ochars++;
    }
    if (ochars > 0) {
        signaln(typtr->tyosem, ochars);
    }

    if ( (typtr->tyehead == typtr->tyetail) &&
         (semcount(typtr->tyosem) >= TY_OBUFLEN) ) {
        ier = csrptr->ier;
        csrptr->ier = (ier & ~UART_IER_ETBEI);
    }
    return;
}