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