VxWorks
BSP Developer's Guide, 6.6
10
2.2 Boot Sequence
This section describes the steps in a typical VxWorks boot scenario and identifies
which routines implement each step. All processors execute the same logical
process in initializing and loading VxWorks, although some may require an extra
step or two and others may skip certain steps.
2.2.1 Sequence Overview
At a minimum, initializing a processor consists of providing a portion of code, and
possibly some tables, that are located at the specific location in memory that the
processor jumps to upon reset or power-up of the target system. This code sets the
processor to a specific state, initializes memory and memory addressing, disables
interrupts, and then passes control to additional bootstrapping code.
Upon power-up or reset, the processor first jumps to the entry point in ROM,
_romInit( ). The assembly code at the jump destination sets up memory, initializes
the processor status word, and creates a temporary stack. The processor then
jumps to a C routine (romStart( ) in installDir/vxworks-6.x/
target/config/
all/bootInit.c). A parameter in a register or on a temporary stack determines
whether memory must be cleared (cold start) and then copies the appropriate
sections of ROM into RAM. If the code in ROM is compressed, it is decompressed
during the copy. Next, the processor jumps to the VxWorks entry point in RAM.
The VxWorks entry point is _sysInit( ) in sysALib.s. This assembly routine sets the
initial hardware state (much as _romInit( ) does) and then jumps to usrInit( ) in
usrConfig.c. usrInit( ) is the first C routine that runs from a VxWorks image. This
routine initializes the cache, clears the block storage segment (bss) to zero,
initializes the vector table, performs board-specific initialization, and then starts
the multitasking kernel with a user-booting task.
Figure 2-1 provides an overview of the boot sequence when VxWorks is booted
from an image.
Figure 2-2 illustrates the boot sequence used when VxWorks is booted from a
ROM-based loader. Note that the boot sequence after usrInit( ) is the same as that
shown in Figure 2-1.
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