cntwus.c

使用广泛的日本著名的开源嵌入式实时操作系统T-Kernel的源码

/*
 *----------------------------------------------------------------------
 *    T-Kernel
 *
 *    Copyright (C) 2004-2006 by Ken Sakamura. All rights reserved.
 *    T-Kernel is distributed under the T-License.
 *----------------------------------------------------------------------
 *
 *    Version:   1.02.02
 *    Released by T-Engine Forum(http://www.t-engine.org) at 2006/8/9.
 *
 *----------------------------------------------------------------------
 */

/*
 *	cntwus.c (M32104)
 *	Loop Count Computation of micro Second Wait 
 */

#include <basic.h>
#include <sys/sysinfo.h>
#include <tk/syslib.h>
#include "tkdev_conf.h"

/*
 * Mode register setting value
 *	TSEL =1	Output timer mode
 *	CCSEL=1	Use constant frequency clock (FCLK)
 *	CSSEL=2	32 dividing
 *	TCSEL=0	Unlimited terminal count number
 *	TCCR =0	Count down limit value 0
 *	TOSEL=0	No timer output
 *	GTSEL=0	No gate/trigger input
 *	CMSEL=0	Count down
 */
#define MFTMOD_INIT	( MFTMOD_TSEL | MFTMOD_CCSEL | MFTMOD_CSSEL(2) )

/*
 * Wait loop
 */
LOCAL void WaitLoop( UW count )
{
	Asm("	_loop:	addi	%0, #-1		\n"
	"		bgtz	%0, _loop	"
		: "=r"(count)
		: "0"(count)
	);
}

/*
 * WaitUsec()  Compute loop count of micro second wait
 *	Suppose that it is executed by interrupt disable.
 */
EXPORT void CountWaitUsec( void )
{
	UH	cnt, sc, ec;

	/* Stop timer */
	out_w(MFTCR, MFTCR_DIS(0));

	/* Set timer mode */
	out_w(MFT0MOD, MFTMOD_INIT);
	out_w(MFT0CUT, 0xffff);		/* Counter initial value */

	/* Start timer count */
	out_w(MFTCR, MFTCR_ENA(0));

	/* Measure time for 110000 loops */
	sc = in_w(MFT0CUT);
	WaitLoop(110000);
	ec = in_w(MFT0CUT);
	cnt = sc - ec;

	/* Measure time for 10000 loops */
	sc = in_w(MFT0CUT);
	WaitLoop(10000);
	ec = in_w(MFT0CUT);

	/* Delete time for operation except for loops and 
	   compute the net time for 100000 loops */
	cnt -= sc - ec;

	/* Stop timer */
	out_w(MFTCR, MFTCR_DIS(0));

	/* Compute number of loops for 64 micro second
	 *			100000 loops
	 *	loop64us = ----------------------- * 64usec
	 *		    cnt * (32 dividing / Fclk)
	 *	Fclk = Constant frequency clock (MHz)
	 */
	SCInfo.loop64us = SCInfo.Fclk * 200000 / cnt;
}