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Reset
InitBoot
Call
SelectBootMode
Read the state
of I/O pins to
determine what
boot mode is
desired
Call
Boot Loader
?
No
Yes
EntryPoint determined
directly from state of
I/O pins
Call
boot loader,
SCI, SPI,
I2C, eCAN, or
parallel I/O
EntryPoint
and load
data/code
Read
Call
ExitBoot
Begin execution
at EntryPoint
Reset
InitBoot
SelectBootMode
Select jump
to flash
ExitBoot
Jump to
0x3F 7FF6
User
programmed
branch to
desired
location
Bootloader Modes
shows an overview of the boot process. Each step is described in greater detail in following
sections.
Figure 2-2. Boot ROM Function Overview
The following boot modes do not call a bootloader. Instead, they jump to a predefined location in memory:
•
Jump to branch instruction in flash memory
In this mode, the boot ROM software will configure the device for 28x operation and then branch
directly to location 0x3F 7FF6 in flash memory. This location is just before the 128-bit code security
module (CSM) password locations. You are required to have previously programmed a branch
instruction at location 0x3F 7FF6 that will redirect code execution to either a custom boot-loader or the
application code.
On RAM-only devices, the boot-to-flash option jumps to reserved memory and should not be used. On
ROM-only devices, the boot-to-flash option jumps to the location 0x3F7FF6 in ROM.
Figure 2-3. Jump-to-Flash Flow Diagram
•
Jump to M0 SARAM
In this mode, the boot ROM software will configure the device for 28x operation and then branch
directly to 0x00 0000; the first address in the M0 SARAM memory block
22
Bootloader Features
SPRU722C – November 2004 – Revised October 2006