diff options
Diffstat (limited to 'nuttx/arch/arm/src/common/up_udelay.c')
-rw-r--r-- | nuttx/arch/arm/src/common/up_udelay.c | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/nuttx/arch/arm/src/common/up_udelay.c b/nuttx/arch/arm/src/common/up_udelay.c new file mode 100644 index 000000000..d2d5b74d9 --- /dev/null +++ b/nuttx/arch/arm/src/common/up_udelay.c @@ -0,0 +1,129 @@ +/**************************************************************************** + * arch/arm/src/common/up_udelay.c + * + * Copyright (C) 2007, 2008 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 NuttX 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 <sys/types.h> +#include <nuttx/arch.h> + +/**************************************************************************** + * Definitions + ****************************************************************************/ + +#define CONFIG_BOARD_LOOPSPER100USEC ((CONFIG_BOARD_LOOPSPERMSEC+5)/10) +#define CONFIG_BOARD_LOOPSPER10USEC ((CONFIG_BOARD_LOOPSPERMSEC+50)/100) +#define CONFIG_BOARD_LOOPSPERUSEC ((CONFIG_BOARD_LOOPSPERMSEC+500)/1000) + +/**************************************************************************** + * 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(useconds_t microseconds) +{ + volatile int i; + + /* We'll do this a little at a time because we expect that the + * CONFIG_BOARD_LOOPSPERUSEC is very inaccurate during to truncation in + * the divisions of its calculation. We'll use the largest values that + * we can in order to prevent significant error buildup in the loops. + */ + + while (microseconds > 1000) + { + for (i = 0; i < CONFIG_BOARD_LOOPSPERMSEC; i++) + { + } + microseconds -= 1000; + } + + while (microseconds > 100) + { + for (i = 0; i < CONFIG_BOARD_LOOPSPER100USEC; i++) + { + } + microseconds -= 100; + } + + while (microseconds > 10) + { + for (i = 0; i < CONFIG_BOARD_LOOPSPER10USEC; i++) + { + } + microseconds -= 10; + } + + while (microseconds > 0) + { + for (i = 0; i < CONFIG_BOARD_LOOPSPERUSEC; i++) + { + } + microseconds--; + } +} |