/*
Copyright (C) Magna Carta Software, Inc. 1990, 1991.  All Rights Reserved
NS16550A.C -- Routines specific to the National Semiconductor NS16550x family.
*/

#include <comm.h>
#if (defined(MSC) || defined(__WATCOMC__) || defined(__HIGHC__))
    #include <conio.h>
#endif



/*
SET_16550_THRESHOLD -- Set the interrupt threshold level and enable the FIFOs
on the NS16550A.
Parameters:
    COMM_PORT *p    -- a ptr. to the port;
    WORD count      -- the desired interrupt threshold level;
        valid values:
            0   -- switch to 16450 mode;
            1   -- interrupt when one character arrives in the buffer;
            4   -- interrupt when four characters arrive in the buffer;
            8   -- interrupt when eight characters arrive in the buffer;
            14  -- interrupt when fourteen characters arrive in the buffer;
Return value:
    EOF -- 16550A not present on the designated port;
    -2  -- invalid 16550A threshold level specified;
    0   -- normal return;
*/
short set_16550_threshold(COMM_PORT *p, WORD count)
{
    short val;

    if (isauart(p->ubase_addr) != 3) return (EOF);
    if (count) {
        switch (count) {
            case 1:
                val = 0;
                break;
            case 4:
                val = 1;
                break;
            case 8:
                val = 2;
                break;
            case 14:
                val = 3;
                break;
            default:
                val = -2;

        }
        if (val != -2) {
            /* INITIALIZE FIFO MODE */
            outp(p->ubase_addr+2, 1);
            /* SET THRESHOLD LEVEL */
            outp(p->ubase_addr+2, (val << 6) | 1);
            p->utype = (val << 8) | (BYTE) NS16550A;
        }
    }
    else {          /* SWITCH TO 16450 MODE */
        outp(p->ubase_addr+2, 0);
    }

    return ((val < 0) ? val : 0);
}