memdisk/dskprobe.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2009 Shao Miller - All Rights Reserved
   4  *
   5  *   This program is free software; you can redistribute it and/or modify
   6  *   it under the terms of the GNU General Public License as published by
   7  *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
   8  *   Boston MA 02111-1307, USA; either version 2 of the License, or
   9  *   (at your option) any later version; incorporated herein by reference.
  10  *
  11  * ----------------------------------------------------------------------- */
  12
  13 /*
  14  * dskprobe.c
  15  *
  16  * Routines for probing BIOS disk drives
  17  */
  18
  19 /*
  20  * Uncomment for debugging
  21  *
  22  * #define DBG_DSKPROBE 1
  23  */
  24
  25 #include <stdint.h>
  26 #include "memdisk.h"
  27 #include "bda.h"
  28 #include "conio.h"
  29
  30 /*
  31  * We will probe a BIOS drive numer using INT 13h, AH=probe
  32  * and will pass along that call's success or failure
  33  */
  34 int probe_int13_ah(uint8_t drive, uint8_t probe)
  35 {
  36     int err;
  37     com32sys_t regs;
  38
  39     memset(&regs, 0, sizeof regs);
  40
  41     regs.eax.b[1] = probe;      /* AH = probe                 */
  42     regs.edx.b[0] = drive;      /* DL = drive number to probe */
  43     intcall(0x13, &regs, &regs);
  44
  45     err = !(regs.eflags.l & 1);
  46 #ifdef DBG_DSKPROBE
  47     printf("probe_int13_ah(0x%02x, 0x%02x) == %d\n", drive, probe, err);
  48 #endif
  49     return err;
  50 }
  51
  52 /*
  53  * We will probe the BIOS Data Area and count the drives found there.
  54  * This heuristic then assumes that all drives of 'drive's type are
  55  * found in a contiguous range, and returns 1 if the probed drive
  56  * is less than or equal to the BDA count.
  57  * This particular function's code is derived from code in setup.c by
  58  * H. Peter Anvin.  Please respect that file's copyright for this function
  59  */
  60 int probe_bda_drive(uint8_t drive)
  61 {
  62     int bios_drives;
  63     int err;
  64
  65     if (drive & 0x80) {
  66         bios_drives = rdz_8(BIOS_HD_COUNT);     /* HDD count */
  67     } else {
  68         uint8_t equip = rdz_8(BIOS_EQUIP);
  69         if (equip & 1)
  70             bios_drives = (equip >> 6) + 1;     /* Floppy count */
  71         else
  72             bios_drives = 0;
  73     }
  74     err = (drive - (drive & 0x80)) >= bios_drives ? 0 : 1;
  75 #ifdef DBG_DSKPROBE
  76     printf("probe_bda_drive(0x%02x) == %d, count: %d\n",
  77            drive, err, bios_drives);
  78 #endif
  79     return err;
  80 }
  81
  82 /*
  83  * We will probe a drive with a few different methods, returning
  84  * the count of succesful probes
  85  */
  86 int probe_drive(uint8_t drive)
  87 {
  88     int c = 0;
  89     /* Only probe the BDA for floppies */
  90     if (drive & 0x80) {
  91         c += probe_int13_ah(drive, 0x08);
  92         c += probe_int13_ah(drive, 0x15);
  93         c += probe_int13_ah(drive, 0x41);
  94     }
  95     c += probe_bda_drive(drive);
  96     return c;
  97 }
  98
  99 /*
 100  * We will probe a contiguous range of BIOS drive, starting with drive
 101  * number 'start'.  We probe with a few different methods, and return
 102  * the first drive which doesn't respond to any of the probes.
 103  */
 104 uint8_t probe_drive_range(uint8_t start)
 105 {
 106     uint8_t drive = start;
 107     while (probe_drive(drive)) {
 108         drive++;
 109         /* Check for passing the floppy/HDD boundary */
 110         if ((drive & 0x7F) == 0)
 111             break;
 112     }
 113     return drive;
 114 }