Subversion Repositories openrisc_2011-10-31

/*-------------------------------------------------------------------------+

| start16.s v1.0 - PC386 BSP - 1998/04/13

+--------------------------------------------------------------------------+

| This file contains the entry point for the application.

| The name of this entry point is compiler dependent.

| It jumps to the BSP which is responsible for performing all initialization.

+--------------------------------------------------------------------------+

| (C) Copyright 1997 -

| - NavIST Group - Real-Time Distributed Systems and Industrial Automation

|

| http://pandora.ist.utl.pt

|

| Instituto Superior Tecnico * Lisboa * PORTUGAL

+--------------------------------------------------------------------------+

| Disclaimer:

|

| This file is provided "AS IS" without warranty of any kind, either

| expressed or implied.

+--------------------------------------------------------------------------*/

/*----------------------------------------------------------------------------+

| Constants

+----------------------------------------------------------------------------*/

.set PROT_CODE_SEG, 0x08        # offset of code segment descriptor into GDT

.set PROT_DATA_SEG, 0x10        # offset of code segment descriptor into GDT

.set CR0_PE,        1           # protected mode flag on CR0 register

.set HDRSTART,      HEADERADDR  # address of start of bin2boot header

.set HDROFF,        0x24        # offset into bin2boot header of start32 addr

.set STACKOFF,      0x200-0x10  # offset to load into %esp, from start of image

 /* #define NEW_GAS */

/*----------------------------------------------------------------------------+

| CODE section

+----------------------------------------------------------------------------*/

.text

        .globl _start16         # entry point

        .globl start16

start16:

_start16:

.code16

        cli                     # DISABLE INTERRUPTS!!!

        movw    %cs, %ax        #

        movw    %ax, %ds        # set the rest of real mode registers

        movw    %ax, %es        #

        movw    %ax, %ss        #

#if defined(RTEMS_VIDEO_80x50)

        /*---------------------------------------------------------------------+

        | Switch VGA video to 80 lines x 50 columns mode. Has to be done before

        | turning protected mode on since it uses BIOS int 10h (video) services.

        +---------------------------------------------------------------------*/

        movw    $0x0003, %ax    # forced set

        int     $0x10

        movw    $0x1112, %ax    # use 8x8 font

        xorb    %bl, %bl

        int     $0x10

        movw    $0x1201, %ax    # turn off cursor emulation

        movb    $0x34, %bl

        int     $0x10

        movb    $0x01, %ah      # define cursor (scan lines 0 to 7)

        movw    $0x0007, %cx

        int     $0x10

#endif /* RTEMS_VIDEO_80x50 */

        /*---------------------------------------------------------------------+

        | Bare PC machines boot in real mode! We have to turn protected mode on.

        +---------------------------------------------------------------------*/

        lgdt    gdtptr - start16        # load Global Descriptor Table

        movl    %cr0, %eax

        orl     $CR0_PE, %eax

        movl    %eax, %cr0              # turn on protected mode

#ifdef NEW_GAS

        ljmpl   $PROT_CODE_SEG, $1f     # flush prefetch queue, and reload %cs

#else

        ljmp    $PROT_CODE_SEG, $1f     # flush prefetch queue, and reload %cs

#endif

.code32

1:

        /*---------------------------------------------------------------------+

        | load the other segment registers

        +---------------------------------------------------------------------*/

        movl    $PROT_DATA_SEG, %eax

        movw    %ax, %ds

        movw    %ax, %es

        movw    %ax, %ss

        movl    $start16 + STACKOFF, %esp       # set up stack pointer

        addl    $start16 + STACKOFF, %ebp       # set up stack pointer

        /*---------------------------------------------------------------------+

        | we have to enable A20 in order to access memory above 1MByte

        +---------------------------------------------------------------------*/

        call    empty_8042

        movb    $0xD1, %al              # command write

        outb    %al, $0x64

        call    empty_8042

        movb    $0xDF, %al              # A20 on

        outb    %al, $0x60

        call    empty_8042

        call    pc386_delay

        call    pc386_delay

        call    pc386_delay

        movl    %cs:HDRSTART + HDROFF, %eax     #

        pushl   %eax                            # jump to start of 32 bit code

        ret                                     #

/*----------------------------------------------------------------------------+

| pc386_delay

+------------------------------------------------------------------------------

| Delay is needed after doing I/O.

|

| The outb version is OK on most machines BUT the loop version ...

|

| will delay for 1us on 1Gz machine, it will take a little bit

| longer on slower machines, however, it does not matter because we

| are going to call this function only a few times

!

| NOTE: Saving the content of the EAX register just in case. - Rosimildo.

+----------------------------------------------------------------------------*/

        .p2align 4

        .globl _pc386_delay

        .globl pc386_delay

pc386_delay:

_pc386_delay:

        pushl   %eax

#if defined(USE_OUTB_FOR_DELAY)

        outb    %al, $0x80      # about 1uS delay on most machines

#else

        movl    $0x200, %eax

pc386_delay1:

        dec     %eax

        jnz     pc386_delay1

#endif

        popl    %eax

        ret

/*----------------------------------------------------------------------------+

| empty_8042

+------------------------------------------------------------------------------

| This routine checks that the keyboard command queue is empty (after emptying

| the output buffers).

| No timeout is used - if this hangs there is something wrong with the machine,

| and we probably couldn't proceed anyway.

+----------------------------------------------------------------------------*/

        .p2align 4

        .globl _empty_8042

        .globl empty_8042

empty_8042:

_empty_8042:

        call    pc386_delay

        inb     $0x64, %al      # 8042 status port

        testb   $0x01, %al      # output buffer?

        jz      no_output

        call    pc386_delay

        in      $0x60, %al      # read it

        jmp     empty_8042

no_output:

        test    $0x02, %al      # is input buffer full?

        jnz     empty_8042      # yes - loop

        ret

/*----------------------------------------------------------------------------+

| DATA section

+----------------------------------------------------------------------------*/

/**************************

* GLOBAL DESCRIPTOR TABLE *

**************************/

        .p2align 4

gdtptr:

        /* we use the NULL descriptor to store the GDT pointer - a trick quite

           nifty due to: Robert Collins (rcollins@x86.org) */

        .word   gdtlen - 1

        .long   gdtptr

        .word   0x0000

        /* code segment */

        .word   0xffff, 0

        .byte   0, 0x9f, 0xcf, 0

        /* data segment */

        .word   0xffff, 0

        .byte   0, 0x93, 0xcf, 0

        .set    gdtlen, . - gdtptr      # length of GDT