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@c  COPYRIGHT (c) 1988-2002.

@c  On-Line Applications Research Corporation (OAR).

@c  All rights reserved.

@c

@c  bsp.t,v 1.1 2002/07/30 21:43:53 joel Exp

@c

@chapter Board Support Packages

@section Introduction

An RTEMS Board Support Package (BSP) must be designed

to support a particular processor and target board combination.

This chapter presents a discussion of XXX specific BSP

issues.   For more information on developing a BSP, refer to the

chapter titled Board Support Packages in the RTEMS

Applications User's Guide.

@section System Reset

An RTEMS based application is initiated or

re-initiated when the XXX processor is reset.  When the

XXX is reset, the processor performs the following actions:

@itemize @bullet

@item The tracing bits of the status register are cleared to

disable tracing.

@item The supervisor interrupt state is entered by setting the

supervisor (S) bit and clearing the master/interrupt (M) bit of

the status register.

@item The interrupt mask of the status register is set to

level 7 to effectively disable all maskable interrupts.

@item The vector base register (VBR) is set to zero.

@item The cache control register (CACR) is set to zero to

disable and freeze the processor cache.

@item The interrupt stack pointer (ISP) is set to the value

stored at vector 0 (bytes 0-3) of the exception vector table

(EVT).

@item The program counter (PC) is set to the value stored at

vector 1 (bytes 4-7) of the EVT.

@item The processor begins execution at the address stored in

the PC.

@end itemize

@section Processor Initialization

The address of the application's initialization code

should be stored in the first vector of the EVT which will allow

the immediate vectoring to the application code.  If the

application requires that the VBR be some value besides zero,

then it should be set to the required value at this point.  All

tasks share the same XXX's VBR value.  Because interrupts

are enabled automatically by RTEMS as part of the initialize

executive directive, the VBR MUST be set before this directive

is invoked to insure correct interrupt vectoring.  If processor

caching is to be utilized, then it should be enabled during the

reset application initialization code.

In addition to the requirements described in the

Board Support Packages chapter of the Applications User's

Manual for the reset code which is executed before the call to

initialize executive, the XXX version has the following

specific requirements:

@itemize @bullet

@item Must leave the S bit of the status register set so that

the XXX remains in the supervisor state.

@item Must set the M bit of the status register to remove the

XXX from the interrupt state.

@item Must set the master stack pointer (MSP) such that a

minimum stack size of MINIMUM_STACK_SIZE bytes is provided for

the initialize executive directive.

@item Must initialize the XXX's vector table.

@end itemize

Note that the BSP is not responsible for allocating

or installing the interrupt stack.  RTEMS does this

automatically as part of initialization.  If the BSP does not

install an interrupt stack and -- for whatever reason -- an

interrupt occurs before initialize_executive is invoked, then

the results are unpredictable.