BSP Developer's Guide

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BSP Organization
The Motorola M68040 must be put in a transparent memory-mapping mode.
The Motorola M683xx family is a special case. These processors run on busless
boards that communicate with the outside world via serial lines; for this reason,
the boot ROMs contain an embedded standalone VxWorks shell
(vxWorks.st_rom.hex). This type of configuration may become more prevalent in
future busless systems.
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2.3.2 Sequence Overview
The processor is first “jumped” to the entry point in ROM, which sets the status
word and creates a dummy stack; then it jumps toaCroutine. A parameter on the
dummy stack determines whether to clear memory (cold start), and then copies the
rest of ROM into RAM (if the remainder of the ROM is compressed, then it is
uncompressed during the copy). Next, the processor jumps to the entry point in
RAM. 2
The RAM entry point in bootConfig.c disables the cache, clears the bss segment to
zero, initializes the vector table, performs board specific initialization, and then
starts the multitasking kernel with a user booting task as its only activity.
The VxWorks boot ROM image is a standalone application in its own right. The
developer uses it to boot a new VxWorks image over the network and link in
application code. The boot ROM’s kernel is discarded; there is no trap mechanism
or reuse of this code. The application is linked with a new image built on the host.
2.3.3 Files and Routines
This section contains a more detailed explanation of how booting takes place,
organized by file and routine name. For clarity, the sequence has been broken
down into a number of main steps or function calls. The key functions are listed as
headings and shown in invocation order.
romInit.s: romInit( )
At power-up (cold start) the processor begins execution at romInit( ), always the
first routine in romInit.s. For warm starts, the processor begins execution at
2. The reason for executing the text segment from RAM is partly for speed (although it is not
faster in all situations), and to allow a uniform model for uncompression, which may be
insufficient reason for an application to retain this model, especially at the cost of wasted
RAM. Either way, the data segment and bss (uninitialized data) must be in RAM.
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