source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/AccessDPT.asm@ 359

Last change on this file since 359 was 358, checked in by aitotat@…, 13 years ago

Changes to XTIDE Universal BIOS:

  • Moved BIOS title and version strings to Version.inc.
  • Moved LBA to L-CHS conversion function to LbaAssist.asm.
File size: 4.8 KB
Line 
1; Project name : XTIDE Universal BIOS
2; Description : Functions for accessing DPT data.
3
4; Section containing code
5SECTION .text
6
7;--------------------------------------------------------------------
8; AccessDPT_GetDriveSelectByteToAL
9; Parameters:
10; DS:DI: Ptr to Disk Parameter Table
11; Returns:
12; AL: Drive Select Byte
13; Corrupts registers:
14; Nothing
15;--------------------------------------------------------------------
16ALIGN JUMP_ALIGN
17AccessDPT_GetDriveSelectByteToAL:
18 mov al, [di+DPT.wFlags]
19 and al, FLG_DRVNHEAD_LBA | FLG_DRVNHEAD_DRV
20 or al, MASK_DRVNHEAD_SET ; Bits set to 1 for old drives
21 ret
22
23
24;--------------------------------------------------------------------
25; AccessDPT_GetDeviceControlByteToAL
26; Parameters:
27; DS:DI: Ptr to Disk Parameter Table
28; Returns:
29; AL: Device Control Byte
30; Corrupts registers:
31; Nothing
32;--------------------------------------------------------------------
33ALIGN JUMP_ALIGN
34AccessDPT_GetDeviceControlByteToAL:
35 xor al, al
36 test BYTE [di+DPT.bFlagsLow], FLGL_DPT_ENABLE_IRQ
37 jnz SHORT .EnableDeviceIrq
38 or al, FLG_DEVCONTROL_nIEN ; Disable IRQ
39.EnableDeviceIrq:
40 ret
41
42
43;--------------------------------------------------------------------
44; AccessDPT_GetLCHStoAXBLBH
45; Parameters:
46; DS:DI: Ptr to Disk Parameter Table
47; Returns:
48; AX: Number of L-CHS cylinders
49; BL: Number of L-CHS heads
50; BH: Number of L-CHS sectors per track
51; Corrupts registers:
52; CX, DX
53;--------------------------------------------------------------------
54AccessDPT_GetLCHStoAXBLBH:
55 ; Return LBA-assisted CHS if LBA addressing used
56 test BYTE [di+DPT.bFlagsLow], FLG_DRVNHEAD_LBA
57 jz SHORT .ConvertPchsToLchs
58
59 call AccessDPT_GetLbaSectorCountToBXDXAX
60 call LbaAssist_ConvertSectorCountFromBXDXAXtoLbaAssistedCHSinDXAXBLBH
61 LIMIT_LBA_CYLINDERS_IN_DXAX_TO_LCHS_CYLINDERS
62 ret
63
64.ConvertPchsToLchs:
65 mov ax, [di+DPT.wPchsCylinders]
66 mov bx, [di+DPT.wPchsHeadsAndSectors]
67 ; Fall to AccessDPT_ShiftPCHinAXBLtoLCH
68
69
70;--------------------------------------------------------------------
71; AccessDPT_ShiftPCHinAXBLtoLCH
72; Parameters:
73; AX: P-CHS cylinders (1...16383)
74; BL: P-CHS heads (1...16)
75; Returns:
76; AX: Number of L-CHS cylinders (1...1024)
77; BL: Number of L-CHS heads (1...255)
78; CX: Number of bits shifted (4 at most)
79; Corrupts registers:
80; Nothing
81;--------------------------------------------------------------------
82AccessDPT_ShiftPCHinAXBLtoLCH:
83 xor cx, cx
84.ShiftLoop:
85 cmp ax, MAX_LCHS_CYLINDERS ; Need to shift?
86 jbe SHORT .Return ; If not, return
87 inc cx ; Increment shift count
88 shr ax, 1 ; Halve cylinders
89 shl bl, 1 ; Double heads
90 jnz SHORT .ShiftLoop ; Falls through only on the last (4th) iteration and only if BL was 16 on entry
91 dec bl ; DOS doesn't support drives with 256 heads so we limit heads to 255
92 ; We can save a byte here by using DEC BX if we don't care about BH
93.Return:
94 ret
95
96
97;--------------------------------------------------------------------
98; AccessDPT_GetLbaSectorCountToBXDXAX
99; Parameters:
100; DS:DI: Ptr to Disk Parameter Table
101; Returns:
102; BX:DX:AX: 48-bit sector count
103; Corrupts registers:
104; Nothing
105;--------------------------------------------------------------------
106AccessDPT_GetLbaSectorCountToBXDXAX:
107 mov ax, [di+DPT.twLbaSectors]
108 mov dx, [di+DPT.twLbaSectors+2]
109 mov bx, [di+DPT.twLbaSectors+4]
110 ret
111
112
113;--------------------------------------------------------------------
114; Returns pointer to DRVPARAMS for master or slave drive.
115;
116; AccessDPT_GetPointerToDRVPARAMStoCSBX
117; Parameters:
118; DS:DI: Ptr to Disk Parameter Table
119; Returns:
120; CS:BX: Ptr to DRVPARAMS
121; Corrupts registers:
122; Nothing
123;--------------------------------------------------------------------
124ALIGN JUMP_ALIGN
125AccessDPT_GetPointerToDRVPARAMStoCSBX:
126 eMOVZX bx, [di+DPT.bIdevarsOffset] ; CS:BX points to IDEVARS
127 add bx, BYTE IDEVARS.drvParamsMaster ; CS:BX points to Master Drive DRVPARAMS
128 test BYTE [di+DPT.bFlagsLow], FLGL_DPT_SLAVE
129 jz SHORT .ReturnPointerToDRVPARAMS
130 add bx, BYTE DRVPARAMS_size ; CS:BX points to Slave Drive DRVPARAMS
131.ReturnPointerToDRVPARAMS:
132 ret
133
134;--------------------------------------------------------------------
135; AccessDPT_GetUnshiftedAddressModeToALZF
136; Parameters:
137; DS:DI: Ptr to Disk Parameter Table
138; Returns:
139; AL: Addressing Mode (L-CHS, P-CHS, LBA28, LBA48)
140; unshifted (still shifted where it is in bFlagsLow)
141; ZF: Set based on value in AL
142; Corrupts registers:
143; AL
144;--------------------------------------------------------------------
145;
146; Converted to a macro since only called in two places, and the call/ret overhead
147; is not worth it for these two instructions (4 bytes total)
148;
149%macro AccessDPT_GetUnshiftedAddressModeToALZF 0
150 mov al, [di+DPT.bFlagsLow]
151 and al, MASKL_DPT_ADDRESSING_MODE
152%endmacro
Note: See TracBrowser for help on using the repository browser.