/*****************************************************************************
			
			fifo.c
			
		    fifo primitives

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


// extern fifotab_t sys_fifot;


/*****************************************************************************
			initialize a fifo 
******************************************************************************/ 

int init_fifo(fifoptr fp)

{	int fifoid;
	//sys_fifot.curridx++;
//	fifoid=sys_fifot.curridx;
//	sys_fifot.fifos[fifoid]=fp;
	fp->state=ALLOCATED; 
	fp->fifo_size=FIFO_SIZE;
	sema_init(&fp->fullsem,0,USYNC_THREAD,0);
	sema_init(&fp->emptysem,fp->fifo_size,USYNC_THREAD,0);
	mutex_init(&fp->fifomut,USYNC_THREAD,0);
	fp->read_idx=0;
	fp->write_idx=0;
	return(fifoid);
}

 
/*****************************************************************************
			read a buffer from a fifo 
******************************************************************************/

bufptr read_fifo(fifoptr fp)

{	bufptr bp;
	sema_wait(&fp->fullsem);
	mutex_lock(&fp->fifomut);
	bp=fp->bufs[fp->read_idx++];
	fp->read_idx %= fp->fifo_size;  
	mutex_unlock(&fp->fifomut);
	sema_post(&fp->emptysem);
       	return(bp);
}



/*****************************************************************************
			write a buffer to a fifo 
******************************************************************************/

int write_fifo(fifoptr fp, bufptr bp)

{ 	
	sema_wait(&fp->emptysem);
	mutex_lock(&fp->fifomut);
	fp->bufs[fp->write_idx++]=bp;
	fp->write_idx %= fp->fifo_size;   
	mutex_unlock(&fp->fifomut);
	sema_post(&fp->fullsem);
 }