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/* Project:     OSLib
 * Description: The OS Construction Kit
 * Date:                1.6.2000
 * Idea by:             Luca Abeni & Gerardo Lamastra
 *
 * OSLib is an SO project aimed at developing a common, easy-to-use
 * low-level infrastructure for developing OS kernels and Embedded
 * Applications; it partially derives from the HARTIK project but it
 * currently is independently developed.
 *
 * OSLib is distributed under GPL License, and some of its code has
 * been derived from the Linux kernel source; also some important
 * ideas come from studying the DJGPP go32 extender.
 *
 * We acknowledge the Linux Community, Free Software Foundation,
 * D.J. Delorie and all the other developers who believe in the
 * freedom of software and ideas.
 *
 * For legalese, check out the included GPL license.
 */

/*      Context switch code     */

#include <ll/i386/sel.h>
#include <ll/i386/linkage.h>
#include <ll/i386/defs.h>

.data          

ASMFILE(Context)

.globl SYMBOL_NAME(currCtx)
.globl JmpSel
.globl JmpZone

SYMBOL_NAME_LABEL(currCtx)      .word   0

JmpZone:
JmpOffset:      
.word   0
.word   0
JmpSel: 
.word   0                 

.text

                .globl SYMBOL_NAME(context_save)
                .globl SYMBOL_NAME(context_change)
                .globl SYMBOL_NAME(context_load)
                .globl SYMBOL_NAME(init_TR)

/* This function assign a value to the TASK register of 386 architecture */
/* We MUST do this BEFORE we use the HW multitask                        */

SYMBOL_NAME_LABEL(init_TR)
                pushl   %ebp
                movl    %esp,%ebp
                movl    8(%ebp),%eax
                ltrw    %ax
                movw    %ax,JmpSel
                movw    %ax,SYMBOL_NAME(currCtx)
                popl    %ebp
                ret
                
/* CONTEXT __cdecl context_save(void);                            */
/* The context is returned into AX; Interrupts are also cleared as we are */
/* entering into kernel primitives                                        */

SYMBOL_NAME_LABEL(context_save)
                        xorl     %eax,%eax
                        strw     %ax
                        ret

/* void __cdecl context_change(CONTEXT c)                               */
/* Use 386 task switch ability. This is the last call of any preemption */
/* generating primitive; when the original task is re-activated the     */
/* interrupt flag is restored with STI                                  */
/* In 32 bit systems, context_load is an alias for context_change!*/

SYMBOL_NAME_LABEL(context_load)
SYMBOL_NAME_LABEL(context_change)       
                        pushl   %ebp
                        movl    %esp,%ebp
                        movw    $(X_FLATDATA_SEL),%ax
                        movw    %ax,%ds
                        movw    %ax,%es
                        movl    8(%ebp),%eax
                        cmpw    JmpSel,%ax
                        je      NoPreempt
                        movw    %ax,JmpSel
                        ljmp    *JmpZone
NoPreempt:              popl    %ebp
                        ret