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##=============================================================================

##

##      romboot.S

##

##      x86 romboot

##

##=============================================================================

## ####ECOSGPLCOPYRIGHTBEGIN####

## -------------------------------------------

## This file is part of eCos, the Embedded Configurable Operating System.

## Copyright (C) 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.

##

## eCos is free software; you can redistribute it and/or modify it under

## the terms of the GNU General Public License as published by the Free

## Software Foundation; either version 2 or (at your option) any later

## version.

##

## eCos is distributed in the hope that it will be useful, but WITHOUT

## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

## FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

## for more details.

##

## You should have received a copy of the GNU General Public License

## along with eCos; if not, write to the Free Software Foundation, Inc.,

## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

##

## As a special exception, if other files instantiate templates or use

## macros or inline functions from this file, or you compile this file

## and link it with other works to produce a work based on this file,

## this file does not by itself cause the resulting work to be covered by

## the GNU General Public License. However the source code for this file

## must still be made available in accordance with section (3) of the GNU

## General Public License v2.

##

## This exception does not invalidate any other reasons why a work based

## on this file might be covered by the GNU General Public License.

## -------------------------------------------

## ####ECOSGPLCOPYRIGHTEND####

##=============================================================================

#######DESCRIPTIONBEGIN####

##

## Author(s):   jskov

## Contributors:jskov

## Date:        1999-01-07

## Purpose:     x86 romboot

## Description: When booting from ROM we need to run a short sequence of real

##              mode code before jumping into 32 bit protected mode. There are

##              problems in GAS with mixing all this code together, and it is

##              easier to just move this bit of code out to a separate file.

##

##

######DESCRIPTIONEND####

##

##=============================================================================

#include 

#include 

#include 

#==============================================================================

//    .file   "romboot.S"

#------------------------------------------------------------------------------

        .code16

romboot_start:

        /* Disable interrupt handling. */

        cli

        # Set DS == CS

        movw    %cs,%ax

        movw    %ax,%ds

        # set ES == 0

        movw    $0,%ax

        movw    %ax,%es

        # Call video bios to init display

        movw    $0xc000,%bx

        movw    %bx,%ds

        movw    0x0000,%ax

        movw    $0x0000,%bx

        movw    %bx,%ds

        cmpw    $0xAA55,%ax

        jne     1f

        .byte   0x9a            # lcall

        .word   0x0003          # offset

        .word   0xc000          # segment

1:

        movw    %cs,%ax

        movw    %ax,%ds

        # set ES == 0

        movw    $0,%ax

        movw    %ax,%es

        # build a GDT descriptor in memory at location zero

        movw    $(gdtEnd - gdtStart),%ax

        movw    %ax,%es:0

        lea     gdtStart,%ax

        addw    $0xFF00,%ax

        movw    %ax,%es:2

        movw    $0x000F,%ax

        movw    %ax,%es:4

        # load GDTR

        lgdt    %es:0

        # Switch to protected mode.

        movl    %cr0,%eax

        orb     $1, %al

        movl    %eax,%cr0

        # and do a jump to flush instruction prefetch

        jmp     romboot_pm

        hlt

        .align  4, 0xCC

gdtStart:

        /* Selector 0x00 == invalid. */

        .word   0x0000

        .word   0x0000

        .byte   0x00

        .byte   0x00

        .byte   0x00

        .byte   0x00

        /* Selector 0x08 == code. */

        .word   0xFFFF

        .word   0x0000

        .byte   0x00

        .byte   0x9B

        .byte   0xCF

        .byte   0x00

        /* Selector 0x10 == data. */

        .word   0xFFFF

        .word   0x0000

        .byte   0x00

        .byte   0x93

        .byte   0xCF

        .byte   0x00

        /* Selector 0x18 == shorter code: faults any code

         * access 0xF0000000-0xFFFFFFFF.

         */

        .word   0xFFFF

        .word   0x0000

        .byte   0x00

        .byte   0x9B

        .byte   0xC7

        .byte   0x00

        /* Selector 0x20 == data; faults any access 0xF0000000-0xFFFFFFFF. */

        .word   0xFFFF

        .word   0x0000

        .byte   0x00

        .byte   0x93

        .byte   0xC7

        .byte   0x00

        .align  4, 0xCC

gdtEnd:

        # We arrive here in protected mode

romboot_pm:

        # Load data selectors

        movw    $0x10, %ax

        movw    %ax, %ds

        movw    %ax, %es

        movw    %ax, %fs

        movw    %ax, %gs

        # jump to start of ROM, where the PM code starts

#       ljmp    $8,$0xF0000

        .byte   0x66,0xea       # opsize + ljmp opcode

        .long   0x000F0000      # destination address

        .word   0x0008          # code selector

        .code16

        .org    0xF0

romboot_reset:

        jmp     romboot_start

        .org    0x100

#------------------------------------------------------------------------------

# end of romboot.S