invert_timer_freq.c

qnx powerpc MPC8245的 BSP源文件

/*
 * $QNXLicenseC: 
 * Copyright 2007, QNX Software Systems.  
 *  
 * Licensed under the Apache License, Version 2.0 (the "License"). You  
 * may not reproduce, modify or distribute this software except in  
 * compliance with the License. You may obtain a copy of the License  
 * at: http://www.apache.org/licenses/LICENSE-2.0  
 *  
 * Unless required by applicable law or agreed to in writing, software  
 * distributed under the License is distributed on an "AS IS" basis,  
 * WITHOUT WARRANTIES OF ANY KIND, either express or implied. 
 * 
 * This file may contain contributions from others, either as  
 * contributors under the License or as licensors under other terms.   
 * Please review this entire file for other proprietary rights or license  
 * notices, as well as the QNX Development Suite License Guide at  
 * http://licensing.qnx.com/license-guide/ for other information. 
 * $ 
 */

#include "startup.h"

//
// Convert the timer frequency (given in Hz) into a timer period and
// store the result into the qtime structure with the highest possible
// precision. This code is system independent and should not have to
// be changed by end users.
//
void
invert_timer_freq(struct qtime_entry *qtime, unsigned freq) {
	int				scale;
	unsigned long	rate;
	unsigned long	rem;
	unsigned long	div;
	unsigned long	quot;

	if(freq == 0) {
		crash("Timer frequency is zero\n");
	}
	quot = 1;
	scale = 0;
	rate = 0;
	for(;;) {
		div = quot / freq;
		rate = rate * 10 + div;
		if(rate >= ((ULONG_MAX/10) - 10)) break;
		rem = quot % freq;
		if(rem == 0) break;
		--scale;
		quot = rem * 10;
	} 
	qtime->timer_rate = rate;
	qtime->timer_scale = scale;
}