114 lines
4.1 KiB
C
114 lines
4.1 KiB
C
/****************************************************************************
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* arch/xtensa/src/common/xtensa_udelay.c
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*
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* Copyright (C) 2016 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <sys/types.h>
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#include <nuttx/arch.h>
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define CONFIG_BOARD_LOOPSPER100USEC ((CONFIG_BOARD_LOOPSPERMSEC+5)/10)
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#define CONFIG_BOARD_LOOPSPER10USEC ((CONFIG_BOARD_LOOPSPERMSEC+50)/100)
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#define CONFIG_BOARD_LOOPSPERUSEC ((CONFIG_BOARD_LOOPSPERMSEC+500)/1000)
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: up_udelay
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*
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* Description:
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* Delay inline for the requested number of microseconds. NOTE: Because
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* of all of the setup, several microseconds will be lost before the actual
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* timing loop begins. Thus, the delay will always be a few microseconds
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* longer than requested.
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*
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* *** NOT multi-tasking friendly ***
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*
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* ASSUMPTIONS:
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* The setting CONFIG_BOARD_LOOPSPERMSEC has been calibrated
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*
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****************************************************************************/
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void up_udelay(useconds_t microseconds)
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{
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volatile int i;
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/* We'll do this a little at a time because we expect that the
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* CONFIG_BOARD_LOOPSPERUSEC is very inaccurate during to truncation in
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* the divisions of its calculation. We'll use the largest values that
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* we can in order to prevent significant error buildup in the loops.
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*/
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while (microseconds > 1000)
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{
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for (i = 0; i < CONFIG_BOARD_LOOPSPERMSEC; i++)
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{
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}
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microseconds -= 1000;
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}
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while (microseconds > 100)
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{
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for (i = 0; i < CONFIG_BOARD_LOOPSPER100USEC; i++)
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{
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}
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microseconds -= 100;
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}
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while (microseconds > 10)
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{
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for (i = 0; i < CONFIG_BOARD_LOOPSPER10USEC; i++)
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{
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}
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microseconds -= 10;
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}
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while (microseconds > 0)
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{
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for (i = 0; i < CONFIG_BOARD_LOOPSPERUSEC; i++)
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{
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}
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microseconds--;
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}
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}
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