/*-------------------------------------------------------------------------+
| ldsegs.s v1.1 - PC386 BSP - 1997/08/07
+--------------------------------------------------------------------------+
| This file assists the board independent startup code by loading the proper
| segment register values. The values loaded are board dependent. In addition
| it contains code to enable the A20 line and to reprogram the PIC to relocate
| the IRQ interrupt vectors to 0x20 -> 0x2f.
| NOTE: No stack has been established when this routine is invoked.
| It returns by jumping back to bspentry.
+--------------------------------------------------------------------------+
| (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 base on:
| ldsegs.s,v 1.4 1996/04/20 16:48:30 joel Exp - go32 BSP
| With the following copyright notice:
| **************************************************************************
| * COPYRIGHT (c) 1989-1998.
| * On-Line Applications Research Corporation (OAR).
| * Copyright assigned to U.S. Government, 1994.
| *
| * The license and distribution terms for this file may be
| * found in found in the file LICENSE in this distribution or at
| * http://www.OARcorp.com/rtems/license.html.
| **************************************************************************
|
| $Id$
|
| Also based on (from the Linux source tree):
| setup.S - Copyright (C) 1991, 1992 Linus Torvalds
+--------------------------------------------------------------------------*/
#include "asm.h"
/*----------------------------------------------------------------------------+
| CODE section
+----------------------------------------------------------------------------*/
BEGIN_CODE
EXTERN (_establish_stack)
EXTERN (Timer_exit)
EXTERN (Clock_exit)
.p2align 4
/*----------------------------------------------------------------------------+
| delay
+------------------------------------------------------------------------------
| Delay is needed after doing I/O. We do it by writing to a non-existent port.
+----------------------------------------------------------------------------*/
SYM(delay):
outb al, $0xED # about 1uS delay
ret
/*-------------------------------------------------------------------------+
| Function: _load_segments
| Description: Current environment is standard PC booted by grub.
| So, there is no value in saving current GDT and IDT
| Settings we have to set it up ourseves. (Naturally
| it will be not so in case we are booted by some
| boot monitor, however, then it will be different
| BSP), After that we have to load board segment registers
| with apropriate values + reprogram PIC.
| Global Variables: None.
| Arguments: None.
| Returns: Nothing.
+--------------------------------------------------------------------------*/
.p2align 4
PUBLIC (_load_segments)
SYM (_load_segments):
lgdt SYM(gdtdesc)
lidt SYM(idtdesc)
/* Load CS, flush prefetched queue */
ljmp $0x8, $next_step
next_step:
/* Load segment registers */
movw $0x10, ax
movw ax, ss
movw ax, ds
movw ax, es
movw ax, fs
movw ax, gs
/* Set default interrupt handler */
movl $0, ecx
movl $Interrupt_descriptor_table, eax
movl $_default_int_handler, ebx
movl ebx, edx
sarl $16, edx
loop:
movw bx, (eax)
movw $0x8, 2(eax)
movw $0x8e00, 4(eax)
movw dx, 8(eax)
addl $8, eax
addl $1, ecx
cmpl $255, ecx
jle loop
/*---------------------------------------------------------------------+
| Now we have to reprogram the interrupts :-(. We put them right after
| the intel-reserved hardware interrupts, at int 0x20-0x2F. There they
| won't mess up anything. Sadly IBM really messed this up with the
| original PC, and they haven't been able to rectify it afterwards. Thus
| the bios puts interrupts at 0x08-0x0f, which is used for the internal
| hardware interrupts as well. We just have to reprogram the 8259's, and
| it isn't fun.
+---------------------------------------------------------------------*/
movb $0x11, al /* initialization sequence */
outb al, $0x20 /* send it to 8259A-1 */
call SYM(delay)
outb al, $0xA0 /* and to 8259A-2 */
call SYM(delay)
movb $0x20, al /* start of hardware int's (0x20) */
outb al, $0x21
call SYM(delay)
movb $0x28, al /* start of hardware int's 2 (0x28) */
outb al, $0xA1
call SYM(delay)
movb $0x04, al /* 8259-1 is master */
outb al, $0x21
call SYM(delay)
movb $0x02, al /* 8259-2 is slave */
outb al, $0xA1
call SYM(delay)
movb $0x01, al /* 8086 mode for both */
outb al, $0x21
call SYM(delay)
outb al, $0xA1
call SYM(delay)
movb $0xFF, al /* mask off all interrupts for now */
outb al, $0xA1
call SYM(delay)
movb $0xFB, al /* mask all irq's but irq2 which */
outb al, $0x21 /* is cascaded */
call SYM(delay)
jmp SYM (_establish_stack) # return to the bsp entry code
/*-------------------------------------------------------------------------+
| Function: _return_to_monitor
| Description: Return to board's monitor (we have none so simply restart).
| Global Variables: None.
| Arguments: None.
| Returns: Nothing.
+--------------------------------------------------------------------------*/
.p2align 4
PUBLIC (_return_to_monitor)
SYM (_return_to_monitor):
call SYM (Timer_exit)
call SYM (Clock_exit)
jmp SYM (start)
/*-------------------------------------------------------------------------+
| Function: _default_int_handler
| Description: default interrupt handler
| Global Variables: None.
| Arguments: None.
| Returns: Nothing.
+--------------------------------------------------------------------------*/
.p2align 4
PUBLIC (_default_int_handler)
SYM (_default_int_handler):
iret
/*---------------------------------------------------------------------------+
| GDT itself
+--------------------------------------------------------------------------*/
.p2align 4
PUBLIC (_Global_descriptor_table)
SYM (_Global_descriptor_table):
/* NULL segment */
.word 0, 0
.byte 0, 0, 0, 0
/* code segment */
.word 0xffff, 0
.byte 0, 0x9e, 0xcf, 0
/* data segment */
.word 0xffff, 0
.byte 0, 0x92, 0xcf, 0
/*---------------------------------------------------------------------------+
| Descriptor of GDT
+--------------------------------------------------------------------------*/
SYM (gdtdesc):
.word (3*8 - 1)
.long SYM (_Global_descriptor_table)
/*---------------------------------------------------------------------------+
| IDT itself
+---------------------------------------------------------------------------*/
.p2align 4
PUBLIC(Interrupt_descriptor_table)
SYM(Interrupt_descriptor_table):
.rept 256
.word 0,0,0,0
.endr
/*---------------------------------------------------------------------------+
| Descriptor of IDT
+--------------------------------------------------------------------------*/
SYM(idtdesc):
.word (256*8 - 1)
.long SYM (Interrupt_descriptor_table)
END_CODE
END
