System Status and Configuration Module (SSCM) RM0391
66.3.3 Boot mode functionality
The device supports the following boot modes for the main boot core:
• User Code Boot mode (SSCM): the device will boot from the first bootable section of the flash memory main array (BOOT_ID = 0x5A).
• BAF Code Boot: the device will boot from UTest NVM Flash Block, (interface with the
HSM if available) and perform device setup (BOOT_ID = 0xA5).
• Standby-Boot : after waking up from Standby Mode, the processor will execute from the
Standby RAM. The flash memory will not be accessible in this mode.
If booting is not possible with the selected configuration (for example, no Boot ID is found in the selected boot location for SSCM and BAF, that is 0x5A and 0xA5 respectively) then the device will enter serial boot mode.
If the HSM is enabled via DCF record, the HSM will boot from the location found via the
HSM boot header search. Refer to Section 66.3.6: HSM boot header search
for details.
66.3.4 BAF configuration
In BAF Code Boot mode the boot core will start to execute the BAF code at the location provided in the “Embedded Flash Memory” chapter (TestFlash block memory map). The
BMODE field in the SSCM status register will be set to the value 0b101. Details of the BAF operation are described in the BAF chapter.
66.3.5 User code boot sector search
66.3.5.1 Potential boot sectors
As shown in
Figure 1799 in User Code Boot mode, several locations are searched for a
valid boot ID. The lowest sector which starts with a valid boot ID will be used to boot the device.
The flash memory locations that are searched for boot information are shown in the “Reset and Boot” chapter (section “HW boot record search (SSCM search)”).
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System Status and Configuration Module (SSCM)
Figure 1799. Flash memory partitioning and RCHW search
5 th
loc
4 th
loc
3 rd
loc
2 nd
loc
$0000 0000
(1 st
location) apps space
Boot information apps space
Boot information apps space
Boot information apps space
Boot information apps space
Boot information
$0000 000C
Application
Application
$0000 0008
$0000 0004
$0000 0000
Application start address
RCHW
66.3.5.2 Reset Configuration Half-Word
For each boot sector in the flash memory, SSCM checks the content of the Reset
Configuration Half-Word (RCHW) at offset 0x00. If the RCHW field BOOT_ID holds the value 0x5A then the sector is considered bootable. In addition, there is a flag which indicates that the code is VLE code. (If a device only supports VLE code for future compatibility the flag must always be set to ‘1’.) All other bits are reserved.
0
R 0
W
Reset 0
1
0
0
2
0
0
3
0
0
4
0
0
5
0
0
6 7
0 VLE
0 0
8
0
9
0
10
0
11 12
BOOT_ID
0 0
13
0
14
0
15
0
= Reserved
Figure 1800. Reset Configuration Half-Word
Once the device detects that it needs to boot from flash memory, and finds a valid
BOOT_ID, it will boot from the application start address at offset 0x04 within the boot sector.
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