PXN20RM Datasheet, PDF (255/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Chapter 9
Boot Assist Module (BAM)
9.1 Introduction
The PXN20 boot assist module (BAM) is a 4 KB block of read-only memory (ROM) that is programmed
by Freescale using variable length encoding (VLE) code. The BAM program is executed by the e200z6
when the PXN20 performs a power-on-reset (POR) or any other reset for which the CRP_Z6VEC register
remains in its reset state. The BAM program provides MCU initialization. It also transitions to the user
application code that resides in the internal flash or downloads the user code into internal RAM via CAN
or SCI serial links and passes control to the user code.
9.1.1 Features
The BAM program provides the following functionality:
• Initial e200z6 core MMU setup with no address translation for all internal MCU resources and
external memory address space
• Location and detection of user boot code in the internal flash
• Automatic switch to serial-boot mode if internal flash is blank or invalid
• Supports user programmable 64-bit password protection for serial-boot mode
• Supports serial bootloading via CAN bus or eSCI to the internal SRAM
• Supports censorship protection for internal flash memory
• Provides an option to disable the error correction status module (ECSM) software watchdog timer
(enabled by default)
• Configures MMU boot block to boot as either classic Power Book E code or as Freescale VLE
code, allowing transition to the user code with classic Power Book E instructions or VLE
instructions
NOTE
The BAM program is intended to be run on e200z6 (main core) only.
Attempting to execute the BAM program by the e200z0 core may cause
erratic MCU behavior.
NOTE
During BAM program execution, the default reset values of various system
registers (e.g. SIU, FlexCAN, eSCI, ECSM, SWT) may be updated from
their default reset values.
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
9-1