PXN20RM Datasheet, PDF (257/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

9.2.2 Register Descriptions
The BAM module does not have any registers.
9.3 Functional Description
Boot Assist Module (BAM)
9.3.1 BAM Program Resources
The BAM program uses/initializes these MCU resources:
• The BOOTCFG field in the reset status register (SIU_RSR) determines the boot option
• The location and value of the reset configuration halfword (RCHW) determines the location of
boot code and the boot configuration options
• FlexCAN_A and eSCI _A modules for serial-boot mode
• FlexCAN_A message buffer RAM for stack and global variables during serial-boot mode
• The DISNEX bit in the SIU_CCR register to determine if the Nexus port is enabled
The BAM program:
• Configures the e200z6 MMU to cover all available MCU address space: internal flash, peripheral
bridge, and SRAM without address translation
• Configures FlexCAN_A, eSCI_A when performing serial-boot mode
• Uses the eDMA during serial-boot mode.
9.3.2 BAM Program Operation
If the CRP_Z6VEC register value is 0xFFFF_FFFC, the BAM code is executed after the negation of reset
and before user code starts. To prevent the execution of the BAM code when exiting sleep mode, change
the value of the CRP_Z6VEC register before entering sleep mode. See Chapter 6, Clocks, Reset, and
Power (CRP), for more detail about the CRP_Z6VEC register.
The BAM reads the status of the BOOTCFG bit from the reset status register (SIU_RSR) and the
appropriate boot sequence is started (see Table 9-2).
Table 9-2 shows the encoding of the BOOTCFG bit in the SIU_RSR, with the value stored in the
Censorship word in the shadow row of internal flash memory. The table also shows whether the internal
flash memory is enabled or disabled, whether the Nexus port is enabled or disabled, and whether the
password downloaded in serial-boot mode is compared with a fixed public password or compared to a user
programmable flash password.
Table 9-2. Boot Modes
Boot Mode Name
Internal—Censored
Internal—Public
BOOTCFG
0
Censorship
Control
0x00FF_FDE0
Serial Boot
Control
0x00FF_FDE2
Internal
Flash
State
Nexus State
Serial
Password
Any other value
0x55AA
Don't care
Enabled
Enabled
Disabled
Enabled
Flash
Public
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
9-3