/*-------------------------------------------------------------------------+
| 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.
+--------------------------------------------------------------------------+
| This code is partly based on (from the Linux source tree):
| video.S - Copyright (C) 1995, 1996 Martin Mares <mj@k332.feld.cvut.cz>
+--------------------------------------------------------------------------*/
/*----------------------------------------------------------------------------+
| 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
/*----------------------------------------------------------------------------+
| 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
ljmp $PROT_CODE_SEG, $1f # flush prefetch queue, and reload %cs
1:
.code32
/*---------------------------------------------------------------------+
| load the other segment registers
+---------------------------------------------------------------------*/
movl $PROT_DATA_SEG, %eax
movl %ax, %ds
movl %ax, %es
movl %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
movl %cs:HDRSTART + HDROFF, %eax #
pushl %eax # jump to start of 32 bit code
ret #
/*----------------------------------------------------------------------------+
| delay
+------------------------------------------------------------------------------
| Delay is needed after doing I/O. We do it by writing to a non-existent port.
+----------------------------------------------------------------------------*/
.globl _delay
.globl delay
delay:
_delay:
outb %al, $0xED # about 1uS delay
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.
+----------------------------------------------------------------------------*/
.globl _empty_8042
.globl empty_8042
empty_8042:
_empty_8042:
call delay
inb $0x64, %al # 8042 status port
testb $0x01, %al # output buffer?
jz no_output
call 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
