toolchain/gcc/libgloss/m68k/idp-inbyte.c

   1 /* idp-inbyte.c --
   2  * Copyright (c) 1995 Cygnus Support
   3  *
   4  * The authors hereby grant permission to use, copy, modify, distribute,
   5  * and license this software and its documentation for any purpose, provided
   6  * that existing copyright notices are retained in all copies and that this
   7  * notice is included verbatim in any distributions. No written agreement,
   8  * license, or royalty fee is required for any of the authorized uses.
   9  * Modifications to this software may be copyrighted by their authors
  10  * and need not follow the licensing terms described here, provided that
  11  * the new terms are clearly indicated on the first page of each file where
  12  * they apply.
  13  */
  14
  15 #include <_ansi.h>
  16 #include "mc68681reg.h"
  17
  18 /*
  19  * The DUART is mapped into the IDP address space in an unusual
  20  * manner.  The mc68681 is an 8 bit device located on the least
  21  * significant byte (byte0) of the data bus.  Bytes 3, 2, and
  22  * one have nothing in them and writes to these locations are
  23  * not valid.
  24  */
  25
  26 #define DUART_ADDR      0x00B00000
  27 #define READREG(x)      (*((volatile char *) DUART_ADDR + (x * 4) + 3))
  28 #define WRITEREG(x, y)  (*((char *) DUART_ADDR + (x * 4) + 3) = y)
  29
  30 /*
  31  * inbyte -- get a byte from the DUART RX buffer. This only reads
  32  *           from channel A
  33  */
  34 char
  35 _DEFUN_VOID (inbyte)
  36 {
  37   while ((READREG (DUART_SRA) & 0x01) == 0x00)
  38     ;
  39
  40   return (READREG (DUART_RBA));         /* read the byte */
  41 }