/****************************************************************************
* common/up_udelay.c
*
* Copyright (C) 2007 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name Gregory Nutt nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/arch.h>
/****************************************************************************
* Definitions
****************************************************************************/
#define CONFIG_BOARD_LOOPSPERUSEC ((CONFIG_BOARD_LOOPSPERMSEC+500)/1000)
#define CONFIG_BOARD_LOOPSPER10USEC ((CONFIG_BOARD_LOOPSPERMSEC+50)/100)
/****************************************************************************
* Private Types
****************************************************************************/
/****************************************************************************
* Private Function Prototypes
****************************************************************************/
/****************************************************************************
* Private Variables
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: up_udelay
*
* Description:
* Delay inline for the requested number of microseconds. NOTE: Because
* of all of the setup, several microseconds will be lost before the actual
* timing looop begins. Thus, the delay will always be a few microseconds
* longer than requested.
*
* *** NOT multi-tasking friendly ***
*
* ASSUMPTIONS:
* The setting CONFIG_BOARD_LOOPSPERMSEC has been calibrated
*
****************************************************************************/
void up_udelay(unsigned int microseconds)
{
volatile int i;
volatile int j;
register uint32 loops;
/* The value of microseconds should be less than 1000. If not, then we
* will perform millescond delays until it is.
*/
while (microseconds > 1000)
{
for (j = 0; j < CONFIG_BOARD_LOOPSPERMSEC; j++)
{
}
microseconds -= 1000;
}
/* The numerator of the 'loops' below will overflow if CONFIG_BOARD_LOOPSPERMSEC
* is larger than (4*1024*1024*1024 - 500)/999 = 4,299,266.06
*/
#if CONFIG_BOARD_LOOPSPERMSEC >= 4299266
while (microseconds > 500)
{
for (j = 0; j < ((CONFIG_BOARD_LOOPSPERMSEC+1)/2); j++)
{
}
microseconds -= 500;
}
#endif
/* The overflow could still occur if CONFIG_BOARD_LOOPSPERMSEC is larger than
* (4*1024*1024*1024 - 500)/499 = 8,607,147.89
*/
#if CONFIG_BOARD_LOOPSPERMSEC >= 8607147
# warning "Overflow in loops calculation is possible"
#endif
/* Caculate the number of loops need to produce the required usec delay */
loops = (CONFIG_BOARD_LOOPSPERMSEC * microseconds + 500) / 1000;
for (j = 0; j < loops; j++)
{
}
}
