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Boot Assist Module (BAM)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
625
The censorship word is a 32-bit word of data stored in the shadow row of internal flash memory. This
memory location is read and interpreted by hardware as part of the boot process and is used in conjunction
with the BOOTCFG pin to enable/disable the internal flash memory and the Nexus interface. The address
of the Censorship word is 0x00FF_FDE0. The censorship word consists of two fields: censorship control
and serial boot control. The censorship word is programmed during manufacturing to be 0x55AA_55AA.
This results in a device that is not censored and uses a Flash-based password for serial boot mode.
Figure 21-2. Censorship word
The BAM program uses the state of bit SIU_CCR[DISNEX] to determine whether the serial password
received in serial boot mode should be compared to a public password (fixed value of the
0xFEED_FACE_CAFE_BEEF) or needs to be compared to a Flash password - 64-bit data, stored in the
shadow row of internal flash at address 0x00FF_FDD8. If the bit is set, the BAM uses the Flash serial
password, if the bit is cleared, it uses the public password.
10
!0x55AA
Any value
External—No
arbitration—Censored
Disable
d
Enabled
Public
0x55AA
External—No arbitration—Public
Enabled Enabled
Public
11
Invalid value
1
‘!’ = ‘NOT,’ as in!0x55AA, means all values except 0x55AA. Do not use 0x0000 or 0xFFFF for the value of the
censorship control or serial boot control words.
Censorship Word @ 0x00FF_FDE0
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
0
Censorship Control - showing an uncensored part (Factory Default)
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0
1
0
1
0
1
0
1
1
0
1
0
1
0
1
0
Serial Boot Control - showing the use of the flash based password (Factory Default)
Table 21-3. Boot modes (continued)
BOOTCFG
[0:1]
Censorship
control
0x00FF_FDE
0
Serial boot
control
0x00FF_FDE
2
Boot mode name
Internal
Flash
state
Nexus
state
Serial
password
Содержание MPC5644A
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