arch/x86/boot/tty.c

   1 /* -*- linux-c -*- ------------------------------------------------------- *
   2  *
   3  *   Copyright (C) 1991, 1992 Linus Torvalds
   4  *   Copyright 2007 rPath, Inc. - All Rights Reserved
   5  *
   6  *   This file is part of the Linux kernel, and is made available under
   7  *   the terms of the GNU General Public License version 2.
   8  *
   9  * ----------------------------------------------------------------------- */
  10
  11 /*
  12  * arch/i386/boot/tty.c
  13  *
  14  * Very simple screen I/O
  15  * XXX: Probably should add very simple serial I/O?
  16  */
  17
  18 #include "boot.h"
  19
  20 /*
  21  * These functions are in .inittext so they can be used to signal
  22  * error during initialization.
  23  */
  24
  25 void __attribute__((section(".inittext"))) putchar(int ch)
  26 {
  27         unsigned char c = ch;
  28
  29         if (c == '\n')
  30                 putchar('\r');  /* \n -> \r\n */
  31
  32         /* int $0x10 is known to have bugs involving touching registers
  33            it shouldn't.  Be extra conservative... */
  34         asm volatile("pushal; pushw %%ds; int $0x10; popw %%ds; popal"
  35                      : : "b" (0x0007), "c" (0x0001), "a" (0x0e00|ch));
  36 }
  37
  38 void __attribute__((section(".inittext"))) puts(const char *str)
  39 {
  40         int n = 0;
  41         while (*str) {
  42                 putchar(*str++);
  43                 n++;
  44         }
  45 }
  46
  47 /*
  48  * Read the CMOS clock through the BIOS, and return the
  49  * seconds in BCD.
  50  */
  51
  52 static u8 gettime(void)
  53 {
  54         u16 ax = 0x0200;
  55         u16 cx, dx;
  56
  57         asm volatile("int $0x1a"
  58                      : "+a" (ax), "=c" (cx), "=d" (dx)
  59                      : : "ebx", "esi", "edi");
  60
  61         return dx >> 8;
  62 }
  63
  64 /*
  65  * Read from the keyboard
  66  */
  67 int getchar(void)
  68 {
  69         u16 ax = 0;
  70         asm volatile("int $0x16" : "+a" (ax));
  71
  72         return ax & 0xff;
  73 }
  74
  75 static int kbd_pending(void)
  76 {
  77         u8 pending;
  78         asm volatile("int $0x16; setnz %0"
  79                      : "=rm" (pending)
  80                      : "a" (0x0100));
  81         return pending;
  82 }
  83
  84 void kbd_flush(void)
  85 {
  86         for (;;) {
  87                 if (!kbd_pending())
  88                         break;
  89                 getchar();
  90         }
  91 }
  92
  93 int getchar_timeout(void)
  94 {
  95         int cnt = 30;
  96         int t0, t1;
  97
  98         t0 = gettime();
  99
 100         while (cnt) {
 101                 if (kbd_pending())
 102                         return getchar();
 103
 104                 t1 = gettime();
 105                 if (t0 != t1) {
 106                         cnt--;
 107                         t0 = t1;
 108                 }
 109         }
 110
 111         return 0;               /* Timeout! */
 112 }