RAM 6.0 BUX II Series Uživatelská příručka stáhnout pdf (Strana 25)

2 Overview of a BSP

2.2 Boot Sequence

This routine must duplicate much of the hardware initialization done by romInit( )

in order to set the run-time state rather than the boot state. Keep in mind that the

board may have been booted using a ROM monitor or hardware debugger. In this

case, the VxWorks boot ROM code, where romInit( ) is located, is not executed and

VxWorks system initialization is not performed. Therefore, failure to duplicate the

initialization code from romInit( ) may result in BSP failure.

Step 4: Execute usrInit( )

The purpose of the usrInit( ) routine is to completely initialize the CPU and shut

down any other hardware, thus preparing the way for the kernel to initialize and

start itself. This routine is located in usrConfig.c but calls routines in several other

files, some of which you must provide and some of which are provided by Wind

River. Normally, it is not necessary to modify the usrInit( ) routine provided by

Wind River. However, the sysHwInit( ) routine that must be called from usrInit( )

typically requires modification. The sysHwInit( ) routine ensures that the

board-dependent hardware is quiescent. sysHwInit( ) is provided in the reference

BSP or template and is located in sysLib.c.

The usrInit( ) routine (in usrConfig.c) saves information about the boot type,

handles all initialization that must be performed before the kernel is actually

started, and then starts the kernel execution. It is the first C code to run in VxWorks.

This routine is invoked in supervisor mode with all hardware interrupts locked

out.

Many facilities cannot be invoked from this routine. Because there is no task

context yet—that is, no task control block (TCB) and no thread 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 itself uses a

facility of this type, such as printf( ). Instead, the usrInit( ) routine does only what

is necessary to create the initial thread, usrRoot( ). usrRoot( ) then completes the

startup.

The initialization operations performed in usrInit( ) include the following:

■

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—C language specifies that all

uninitialized variables (stored in bss) must have initial values of 0. Because

usrInit( ) is the first C code to execute, it clears the section of memory

containing bss.

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RAM 6.0 BUX II Series Uživatelská příručka Strana 25