delay.h

atmega16L单片机串口使用范例

/* Copyright (c) 2002, Marek Michalkiewicz
   Copyright (c) 2004,2005 Joerg Wunsch
   All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:

   * Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.

   * 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.

   * Neither the name of the copyright holders nor the names of
     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. */

/* $Id: delay.h,v 1.9.2.2 2005/09/10 21:33:13 joerg_wunsch Exp $ */

/*
   avr/delay.h - loops for small accurate delays
 */

#ifndef _AVR_DELAY_H_
#define _AVR_DELAY_H_ 1

#include <inttypes.h>

/** \defgroup avr_delay Busy-wait delay loops
    \code
    #define F_CPU 1000000UL  // 1 MHz
    //#define F_CPU 14.7456E6
    #include <avr/delay.h>
    \endcode

    \note As an alternative method, it is possible to pass the
    F_CPU macro down to the compiler from the Makefile.
    Obviously, in that case, no \c \#define statement should be
    used.

    The functions in this header file implement simple delay loops
    that perform a busy-waiting.  They are typically used to
    facilitate short delays in the program execution.  They are
    implemented as count-down loops with a well-known CPU cycle
    count per loop iteration.  As such, no other processing can
    occur simultaneously.  It should be kept in mind that the
    functions described here do not disable interrupts.

    In general, for long delays, the use of hardware timers is
    much preferrable, as they free the CPU, and allow for
    concurrent processing of other events while the timer is
    running.  However, in particular for very short delays, the
    overhead of setting up a hardware timer is too much compared
    to the overall delay time.

    Two inline functions are provided for the actual delay algorithms.

    Two wrapper functions allow the specification of microsecond, and
    millisecond delays directly, using the application-supplied macro
    F_CPU as the CPU clock frequency (in Hertz).  These functions
    operate on double typed arguments, however when optimization is
    turned on, the entire floating-point calculation will be done at
    compile-time.

    \note When using _delay_us() and _delay_ms(), the expressions
    passed as arguments to these functions shall be compile-time
    constants, otherwise the floating-point calculations to setup the
    loops will be done at run-time, thereby drastically increasing
    both the resulting code size, as well as the time required to
    setup the loops.
*/

#if !defined(DOXYGEN)
static void _delay_loop_1(uint8_t __count) __attribute__((always_inline));
static void _delay_loop_2(uint16_t __count) __attribute__((always_inline));
static void _delay_us(double __us) __attribute__((always_inline));
static void _delay_ms(double __ms) __attribute__((always_inline));
#endif

/** \ingroup avr_delay

    Delay loop using an 8-bit counter \c __count, so up to 256
    iterations are possible.  (The value 256 would have to be passed
    as 0.)  The loop executes three CPU cycles per iteration, not
    including the overhead the compiler needs to setup the counter
    register.

    Thus, at a CPU speed of 1 MHz, delays of up to 768 microseconds
    can be achieved.
*/
void
_delay_loop_1(uint8_t __count)
{
	__asm__ volatile (
		"1: dec %0" "\n\t"
		"brne 1b"
		: "=r" (__count)
		: "0" (__count)
	);
}

/** \ingroup avr_delay

    Delay loop using a 16-bit counter \c __count, so up to 65536
    iterations are possible.  (The value 65536 would have to be
    passed as 0.)  The loop executes four CPU cycles per iteration,
    not including the overhead the compiler requires to setup the
    counter register pair.

    Thus, at a CPU speed of 1 MHz, delays of up to about 262.1
    milliseconds can be achieved.
 */
void
_delay_loop_2(uint16_t __count)
{
	__asm__ volatile (
		"1: sbiw %0,1" "\n\t"
		"brne 1b"
		: "=w" (__count)
		: "0" (__count)
	);
}

#ifndef F_CPU
/* prevent compiler error by supplying a default */
# warning "F_CPU not defined for <avr/delay.h>"
# define F_CPU 1000000UL
#endif

/**
   \ingroup avr_delay

   Perform a delay of \c __us microseconds, using _delay_loop_1().

   The macro F_CPU is supposed to be defined to a
   constant defining the CPU clock frequency (in Hertz).

   The maximal possible delay is 768 us / F_CPU in MHz.
 */
void
_delay_us(double __us)
{
	uint8_t __ticks;
	double __tmp = ((F_CPU) / 3e6) * __us;
	if (__tmp < 1.0)
		__ticks = 1;
	else if (__tmp > 255)
		__ticks = 0;	/* i.e. 256 */
	else
		__ticks = (uint8_t)__tmp;
	_delay_loop_1(__ticks);
}


/**
   \ingroup avr_delay

   Perform a delay of \c __ms milliseconds, using _delay_loop_2().

   The macro F_CPU is supposed to be defined to a
   constant defining the CPU clock frequency (in Hertz).

   The maximal possible delay is 262.14 ms / F_CPU in MHz.
 */
void
_delay_ms(double __ms)
{
	uint16_t __ticks;
	double __tmp = ((F_CPU) / 4e3) * __ms;
	if (__tmp < 1.0)
		__ticks = 1;
	else if (__tmp > 65535)
		__ticks = 0;	/* i.e. 65536 */
	else
		__ticks = (uint16_t)__tmp;
	_delay_loop_2(__ticks);
}

#endif /* _AVR_DELAY_H_ */