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
_DEFUN_VOID(inbyte)35 _DEFUN_VOID (inbyte)
36 {
37 while ((READREG (DUART_SRA) & 0x01) == 0x00)
38 ;
39
40 return (READREG (DUART_RBA)); /* read the byte */
41 }
42