PXS20RM Datasheet, PDF (146/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Boot Assist Module (BAM)
8.4.2.2 BAM software flow
Figure 8-2 describes the BAM logic flow.
BAM entry
0xFFFF_C000
Save default
configuration.
Check boot mode.
Which boot mode is selected is verified by reading
the SSCM_STATUS register (BMODE).
Boot
No
mode valid
?
Yes
Restore default
configuration.
STATIC mode.
Download new code
and save it into SRAM.
Restore default
configuration.
Execute new code.
Figure 8-2. BAM logic flow
The first action is to save the initial device configuration. In this way it is possible to restore the initial
configuration after downloading the new code but before executing it. This allows the new code to be
executed as the device was just coming out of reset.
The SSCM_STATUS[BMODE] field (see Section 48.3.1.1, System Status Register (STATUS)) indicates
which boot has to be executed (see Table 8-3).
If BMODE field shows either a single chip value (011) or the reserved values, the boot mode is not
considered valid and the BAM pushes the device into static mode.
In all other cases data is downloaded in serial boot mode and saved into the correct SRAM location.
Table 8-3. Fields of SSCM STATUS register read by BAM to detect the chosen boot mode
Field
Description
BMODE BMODE Device Boot Mode.
000 Serial Boot Loader (FlexCAN or LINFlex) with autobaud
001 FlexCAN Serial Boot Loader (without autobaud)
010 LINFlex Serial Boot Loader (without autobaud)
011 Single Chip
other values are reserved
Then, the initial device configuration is restored and the code jumps to the address provided for the
downloaded code. At this point BAM has just finished its task.
PXS20 Microcontroller Reference Manual, Rev. 1
8-4
Freescale Semiconductor