BSP Developer's Guide

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BSP Organization
Many VxWorks facilities cannot be invoked from this routine. Because there is no
task context as yet (no TCB and no task stack), facilities that require a task context
cannot be invoked. This includes any facility that can cause the caller to be
preempted, such as semaphores, or any facility that uses such facilities, such as
printf( ). Instead, the usrInit( ) routine does only what is necessary to create an
initial task, usrRoot( ). This task then completes the startup.
The initialization in usrInit( ) includes the following:
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Cache Initialization. The code at the beginning of usrInit( ) initializes the
caches, sets the mode of the caches and puts the caches in a safe state. At the
end of usrInit( ), the instruction and data caches are enabled by default.
Zeroing Out the System bss Segment. The C and C++ languages specify that
all uninitialized variables must have initial values of 0. These uninitialized
variables are put together in a segment called the bss. This segment is not
actually loaded during the bootstrap, because it is known to be zeroed out.
Because usrInit( ) is the first C code to execute, it clears the section of memory
containing bss as its very first action. While the VxWorks boot ROMs clear all
memory, VxWorks does not assume that the boot ROMs are used.
Initializing Interrupt Vectors. The exception vectors must be set up before
enabling interrupts and starting the kernel. First, intVecBaseSet( ) is called to
establish the vector table base address.
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! CAUTION: For some architectures, there are exceptions to the rule that
intVecBaseSet( ) must be called before enabling interrupts and starting the kernel.
See the appropriate VxWorks Architecture Supplement document.
After intVecBaseSet( ) is called, the routine excVecInit( ) initializes all exception
vectors to default handlers that safely trap and report exceptions caused by
program errors or unexpected hardware interrupts.
Initializing System Hardware to a Quiescent State. System hardware is initialized
by calling the system-dependent routine sysHwInit( ). This mainly consists of
resetting and disabling hardware devices that can cause interrupts after interrupts
are enabled (when the kernel is started). This is important because VxWorks ISRs
(for I/O devices, system clocks, and so on) are not connected to their interrupt
vectors until the system initialization is completed in the usrRoot( ) task. However,
because the memory pool is not yet initialized, you must not try to connect an
interrupt handler to an interrupt during the sysHwInit( ) call.
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