RM0046 Boot Assist Module (BAM)
Doc ID 16912 Rev 5 815/936
If public access is not allowed but the flash is not secured, the received password is
compared with the value saved on NVPWD0 and NVPWD1 registers.
In uncensored devices, it is possible to download code via LINFlex or FlexCAN (serial boot
mode) into internal SRAM with any 64-bit private password stored in the flash and provided
during the boot sequence.
In the previous cases, comparison is done by the BAM application. If it goes wrong, BAM
pushes the device into static mode.
In case of public access not allowed and flash secured, the password is written into
SSCM[PWCMPH/L] registers.
In case of flash secured with public access not allowed (user password configured in the
NVPWD0 and NVPWD1 registers), the user must set the swapped password: NVPWD1 and
NVPWD0 to access the device (refer to following examples).
Example 15
In devices with flash secured, registers are programmed:
NVPWD0 = 0x87654321
NVPWD1 = 0x12345678
NVSCI0 = 0x55AA1111
NVSCI1 = 0x55AA1111
To download the code via SLB, the provided password is 0x1234_5678_8765_4321
(swapped WITH respect to NVPWD0/NVPWD1 —> NVPWD1/NVPWD0).
Example 16
In devices with flash NOT secured, registers are programmed:
NVPWD0 = 0x87654321
NVPWD1 = 0x12345678
NVSCI0 = 0x55AA55AA
NVSCI1 = 0x55AA55AA
To download the code via SLB the provided password is 0x8765_4321_1234_5678 (as
expected from NVPWD0/NVPWD1).
After a fixed time waiting, comparison is done by hardware. Then BAM again verifies the
SEC flag in SSCM_STATUS:
● SEC = 0, flash is now unsecured and BAM continues its task
● SEC = 1, flash is still secured because password was wrong; BAM puts the device into
static mode.
This fixed time depends on external crystal oscillator frequency (XOSC). With XOSC of
12 MHz, fixed time is 350 ms.
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