1. 根目录:
2. arch
3. h8300
4. include
5. asm
6. switch_to.h

#ifndef _H8300_SWITCH_TO_H
#define _H8300_SWITCH_TO_H

/*
 * switch_to(n) should switch tasks to task ptr, first checking that
 * ptr isn't the current task, in which case it does nothing.  This
 * also clears the TS-flag if the task we switched to has used the
 * math co-processor latest.
 */
/*
 * switch_to() saves the extra registers, that are not saved
 * automatically by SAVE_SWITCH_STACK in resume(), ie. d0-d5 and
 * a0-a1. Some of these are used by schedule() and its predecessors
 * and so we might get see unexpected behaviors when a task returns
 * with unexpected register values.
 *
 * syscall stores these registers itself and none of them are used
 * by syscall after the function in the syscall has been called.
 *
 * Beware that resume now expects *next to be in d1 and the offset of
 * tss to be in a1. This saves a few instructions as we no longer have
 * to push them onto the stack and read them back right after.
 *
 * 02/17/96 - Jes Sorensen (jds@kom.auc.dk)
 *
 * Changed 96/09/19 by Andreas Schwab
 * pass prev in a0, next in a1, offset of tss in d1, and whether
 * the mm structures are shared in d2 (to avoid atc flushing).
 *
 * H8/300 Porting 2002/09/04 Yoshinori Sato
 */

asmlinkage void resume(void);
#define switch_to(prev,next,last) {                         \
  void *_last;						    \
  __asm__ __volatile__(					    \
  			"mov.l	%1, er0\n\t"		    \
			"mov.l	%2, er1\n\t"		    \
                        "mov.l  %3, er2\n\t"                \
			"jsr @_resume\n\t"                  \
                        "mov.l  er2,%0\n\t"                 \
		       : "=r" (_last)			    \
		       : "r" (&(prev->thread)),		    \
			 "r" (&(next->thread)),		    \
                         "g" (prev)                         \
		       : "cc", "er0", "er1", "er2", "er3"); \
  (last) = _last; 					    \
}

#endif /* _H8300_SWITCH_TO_H */