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
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
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
.
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
Copyright © 2011–2013, Texas Instruments Incorporated