cntwus.c

日本著名的的嵌入式实时操作系统T-Kernel的源码及用户手册。

/*
 *----------------------------------------------------------------------
 *    T-Kernel
 *
 *    Copyright (C) 2004 by Ken Sakamura. All rights reserved.
 *    T-Kernel is distributed under the T-License.
 *----------------------------------------------------------------------
 *
 *    Version:   1.01.00
 *    Released by T-Engine Forum(http://www.t-engine.org) at 2004/6/28.
 *
 *----------------------------------------------------------------------
 */

/*
 *	cntwus.c (S1C38K)
 *	Loop Count Computation of micro Second Wait 
 */

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

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

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

	/* Select timer */
	out_w(TM_SEL, TM_SEL1);

	/* Set timer mode/Stop timer */
	mod = TMC_FREE|TMC_RELOAD|TMC_DIV16;
	out_w(TM1_CTRL, mod);
	out_w(TM1_LOAD, 0xffff);	/* Counter initial value */

	/* Start timer count */
	out_w(TM1_CTRL, mod | TMC_ENA);

	/* Measure time for 110000 loops */
	sc = in_w(TM1_COUNT);
	WaitLoop(110000);
	ec = in_w(TM1_COUNT);
	cnt = sc - ec;

	/* Measure time for 10000 loops */
	sc = in_w(TM1_COUNT);
	WaitLoop(10000);
	ec = in_w(TM1_COUNT);

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

	/* Stop timer */
	out_w(TM1_CTRL, 0);

	/* Compute number of loops for 64 micro second
	 *			100000 loops
	 *	loop64us = ----------------------- * 64usec
	 *		    cnt * (16 dividing / TMCLK)
	 *	TMCLK = Timer input clock (MHz)
	 */
	SCInfo.loop64us = TMCLK * 400000 / cnt;
}