Changeset 324 in xtideuniversalbios for trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/AccessDPT.asm

Timestamp:

Mar 11, 2012, 6:45:03 PM (13 years ago)

Author:

aitotat@…

google:author:

aitotat@gmail.com

Message:

Changes to XTIDE Universal BIOS:

• Boot Menu now displays correct capacity when using user defined LBA.

File:

• trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/AccessDPT.asm (modified) (2 diffs)

trunk/XTIDE_Universal_BIOS/Src/VariablesAndDPTs/AccessDPT.asm

@@ -58 +58 @@
 
     call    AccessDPT_GetLbaSectorCountToBXDXAX
-    call    AtaID_GetLbaAssistedCHStoDXAXBLBH
+    call    AccessDPT_ConvertSectorCountFromBXDXAXtoLbaAssistedCHSinDXAXBLBH
     test    dx, dx
     jnz     SHORT .LimitAXtoMaxLCHScylinders
@@ -157 +157 @@
     and     al, MASKL_DPT_ADDRESSING_MODE
 %endmacro
+
+
+;--------------------------------------------------------------------
+; LBA assist calculation:
+; this is how to fit a big drive into INT13's skimpy size requirements,
+; with a maximum of 8.4G available.
+;
+; total LBAs (as obtained by words 60+61)
+; divided by 63 (sectors per track) (save as value A)
+; Sub 1 from A
+; divide A by 1024 + truncate.
+; == total number of heads to use.
+; add 1
+; this value must be either 16, 32, 64, 128, or 256 (round up)
+; then take the value A above and divide by # of heads
+; to get the # of cylinders to use.
+;
+;
+; so a LBA28 drive will have 268,435,456 as maximum LBAs
+;
+; 10000000h / 63   = 410410h (total cylinders or tracks)
+;   410410h / 1024 = 1041h, which is way more than 256 heads, but 256 is max.
+;   410410h / 256  = 4104h cylinders
+;
+; there's a wealth of information at: http://www.mossywell.com/boot-sequence
+; they show a slightly different approach to LBA assist calulations, but
+; the method here provides compatibility with phoenix BIOS
+;
+; we're using the values from 60+61 here because we're topping out at 8.4G
+; anyway, so there's no need to use the 48bit LBA values.
+;
+; AccessDPT_ConvertSectorCountFromBXDXAXtoLbaAssistedCHStoDXAXBLBH:
+;   Parameters:
+;       BX:DX:AX:   Total number of sectors
+;   Returns:
+;       DX:AX:  Number of cylinders
+;       BH:     Number of sectors per track (always 63)
+;       BL:     Number of heads (16, 32, 64, 128 or 255)
+;   Corrupts registers:
+;       CX
+;--------------------------------------------------------------------
+AccessDPT_ConvertSectorCountFromBXDXAXtoLbaAssistedCHSinDXAXBLBH:
+    push    bp
+    push    si
+
+    ; Value A = Total sector count / 63
+    xor     cx, cx
+    push    cx      ; Push zero for bits 48...63
+    push    bx
+    push    dx
+    push    ax                      ; 64-bit sector count now in stack
+    mov     cl, LBA_ASSIST_SPT
+    mov     bp, sp                  ; SS:BP now points sector count
+    call    Math_DivQWatSSBPbyCX    ; Temporary value A now in stack
+
+    ; BX = Number of heads =  A / 1024
+    mov     ax, [bp]
+    mov     dx, [bp+2]
+    mov     bx, [bp+4]
+    call    Size_DivideSizeInBXDXAXby1024andIncrementMagnitudeInCX
+
+    ; Heads must be 16, 32, 64, 128 or 256 (round up)
+    mov     bx, 256                     ; Max number of heads
+    test    dx, dx                      ; 65536 or more heads?
+    jnz     SHORT .GetNumberOfCylinders
+    mov     cx, 128                     ; Half BX for rounding up
+.FindMostSignificantBitForHeadSize:
+    cmp     ax, cx
+    jae     SHORT .GetNumberOfCylinders
+    shr     cx, 1
+    shr     bx, 1                       ; Halve number of heads
+    jmp     SHORT .FindMostSignificantBitForHeadSize
+
+    ; DX:AX = Number of cylinders = A / number of heads
+.GetNumberOfCylinders:
+    mov     cx, bx
+    call    Math_DivQWatSSBPbyCX
+    mov     ax, [bp]
+    mov     dx, [bp+2]                  ; Cylinders now in DX:AX
+
+    ; Return LBA assisted CHS
+    add     sp, BYTE 8                  ; Clean stack
+    sub     bl, bh                      ; Limit heads to 255
+    mov     bh, LBA_ASSIST_SPT
+    pop     si
+    pop     bp
+    ret