source: xtideuniversalbios/trunk/Assembly_Library/Src/File/Drive.asm@ 314

Last change on this file since 314 was 181, checked in by krille_n_@…, 13 years ago

Changes to all parts of the project:

  • Size optimizations.
  • Added a define (EXCLUDE_FROM_XTIDECFG) to exclude unused library code from XTIDECFG.
  • Tried to minimize time spent with interrupts disabled.
  • Some minor attempts to improve speed (reordering instructions etc).
  • Tried to improve readability, did some cleanup and fixed some errors in comments.
File size: 4.7 KB
Line 
1; Project name : Assembly Library
2; Description : Functions for accessing drives.
3
4
5; Section containing code
6SECTION .text
7
8;--------------------------------------------------------------------
9; Drive_GetNumberOfAvailableDrivesToAX
10; Parameters:
11; Nothing
12; Returns:
13; AX: Number of available drives
14; Corrupts registers:
15; Nothing
16;--------------------------------------------------------------------
17ALIGN JUMP_ALIGN
18Drive_GetNumberOfAvailableDrivesToAX:
19 push dx
20 push cx
21
22 call Drive_GetFlagsForAvailableDrivesToDXAX
23 call Bit_GetSetCountToCXfromDXAX
24 xchg ax, cx
25
26 pop cx
27 pop dx
28 ret
29
30
31;--------------------------------------------------------------------
32; Drive_GetFlagsForAvailableDrivesToDXAX
33; Parameters:
34; Nothing
35; Returns:
36; DX:AX: Flags containing valid drives (bit 0 = drive A, bit 1 = drive B ...)
37; Corrupts registers:
38; Nothing
39;--------------------------------------------------------------------
40ALIGN JUMP_ALIGN
41Drive_GetFlagsForAvailableDrivesToDXAX:
42 push cx
43 push bx
44 mov dx, DosCritical_HandlerToIgnoreAllErrors
45 call DosCritical_InstallNewHandlerFromCSDX
46
47 call .GetNumberOfPotentiallyValidDriveLettersToCX
48 xor bx, bx
49 xor ax, ax ; Temporary use BX:AX for flags
50 cwd ; Start from drive 0
51 call .CheckDriveValidityUntilCXisZero
52 mov dx, bx ; Flags now in DX:AX
53
54 call DosCritical_RestoreDosHandler
55 pop bx
56 pop cx
57 ret
58
59;--------------------------------------------------------------------
60; .GetNumberOfPotentiallyValidDriveLettersToCX
61; Parameters:
62; Nothing
63; Returns:
64; CX: Number of potentially valid drive letters available
65; Corrupts registers:
66; AX, DX
67;--------------------------------------------------------------------
68ALIGN JUMP_ALIGN
69.GetNumberOfPotentiallyValidDriveLettersToCX:
70 call Drive_GetDefaultToAL
71 xchg dx, ax ; Default drive to DL
72 call Drive_SetDefaultFromDL
73 eMOVZX cx, al ; Number of potentially valid drive letters available
74 cmp cl, 32
75 jb SHORT .Return
76 mov cl, 32
77ALIGN JUMP_ALIGN, ret
78.Return:
79 ret
80
81;--------------------------------------------------------------------
82; .CheckDriveValidityUntilCXisZero
83; Parameters:
84; CX: Number of potentially valid drive letters left
85; DL: Drive number (00h=A:, 01h=B: ...)
86; BX:AX: Flags for drive numbers
87; Returns:
88; BX:AX: Flags for valid drive numbers
89; Corrupts registers:
90; CX, DX
91;--------------------------------------------------------------------
92ALIGN JUMP_ALIGN
93.CheckDriveValidityUntilCXisZero:
94 call .IsValidDriveNumberInDL
95 jnz SHORT .PrepareToCheckNextDrive
96 call .SetFlagToBXAXfromDriveInDL
97ALIGN JUMP_ALIGN
98.PrepareToCheckNextDrive:
99 inc dx
100 loop .CheckDriveValidityUntilCXisZero
101 ret
102
103;--------------------------------------------------------------------
104; .IsValidDriveNumberInDL
105; Parameters:
106; DL: Drive number (00h=A:, 01h=B: ...)
107; Returns:
108; ZF: Set if drive number is valid
109; Cleared if drive number is invalid
110; Corrupts registers:
111; Nothing
112;--------------------------------------------------------------------
113ALIGN JUMP_ALIGN
114.IsValidDriveNumberInDL:
115 push ds
116 push bx
117 push ax
118
119 inc dx ; Default drive is 00h and first drive is 01h
120 mov ah, GET_DOS_DRIVE_PARAMETER_BLOCK_FOR_SPECIFIC_DRIVE
121 int DOS_INTERRUPT_21h
122 dec dx
123 test al, al
124
125 pop ax
126 pop bx
127 pop ds
128 ret
129
130;--------------------------------------------------------------------
131; .SetFlagToBXAXfromDriveInDL
132; Parameters:
133; DL: Drive number (0...31)
134; BX:AX: Flags containing drive numbers
135; Returns:
136; BX:AX: Flags with wanted drive bit set
137; Corrupts registers:
138; Nothing
139;--------------------------------------------------------------------
140ALIGN JUMP_ALIGN
141.SetFlagToBXAXfromDriveInDL:
142 push cx
143
144 mov cl, dl
145 xchg dx, bx
146 call Bit_SetToDXAXfromIndexInCL
147 xchg bx, dx
148
149 pop cx
150 ret
151
152
153;--------------------------------------------------------------------
154; Drive_GetDefaultToAL
155; Parameters:
156; Nothing
157; Returns:
158; AL: Current default drive (00h=A:, 01h=B: ...)
159; Corrupts registers:
160; AH
161;--------------------------------------------------------------------
162ALIGN JUMP_ALIGN
163Drive_GetDefaultToAL:
164 mov ah, GET_CURRENT_DEFAULT_DRIVE
165 SKIP2B f ; cmp ax, <next instruction>
166 ; Fall to Drive_SetDefaultFromDL
167
168
169;--------------------------------------------------------------------
170; Drive_SetDefaultFromDL
171; Parameters:
172; DL: New default drive (00h=A:, 01h=B: ...)
173; Returns:
174; AL: Number of potentially valid drive letters available
175; Corrupts registers:
176; AH
177;--------------------------------------------------------------------
178Drive_SetDefaultFromDL:
179 mov ah, SELECT_DEFAULT_DRIVE
180 int DOS_INTERRUPT_21h
181 ret
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