0xAA55 Signature
at offset 0x01FE ?
MBR detection
Is partition
within
physical
boundaries?
Partition type
is 0x00 ?
Yes
No
Success
Failed
No
Yes
Are all fields
0x00 ?
Yes
No
No
For all 4 entries
Yes
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Functional Description
Table 26-23. Partition Entry
Offset Length[bytes] Entry Description Value
0000h 1 Partition State 00h: Inactive80h: Active
0001h 1 Partition Start Head H
s
Partition Start Cylinder and
0002h 2 C
s
[7:0]-C
s
[9:8]-S
s
[5:0]
Sector
See Table 26-24 for partial
0004h 1 Partition Type
partition types
0005h 16 Partition End Head H
e
Partition End Cylinder and
0006h 2 C
e
[7:0]-C
e
[9:8]-S
e
[5:0]
Sector
First sector position relative to
0008h 4 LBA
s
=C
s
.H.S+ H
s
.S+ S
s
-1
the beginning of media
LBA
e
=C
e
.H.S+ H
e
.S+ S
e
-1Nbs=
000Ch 4 Number of sectors in partition
LBA
e
-LBA
s
+1
Table 26-24. Partition Types
Partition Type Description
01h FAT12
04h, 06h, 0Eh FAT16
0Bh, 0Ch, 0Fh FAT32
The way the ROM Code detects whether a sector is the 1
st
sector of an MBR or not is described in
Figure 26-20.
The ROM Code first checks if the signature is present. Each partition entry is checked:
• If its type is set to 00h then all fields in the entry must be 00h
• The partition is checked to be within physical boundaries, i.e. the partition is located inside and it’s size
fits the total physical sectors.
Figure 26-20. MBR Detection Procedure
4135
SPRUH73H–October 2011–Revised April 2013 Initialization
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