# delay_basic.h

/* Copyright (c) 2002, Marek Michalkiewicz

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. */

/* $Id$ */

#ifndef _UTIL_DELAY_BASIC_H_
#define _UTIL_DELAY_BASIC_H_ 1

#include <inttypes.h>

#if !defined(__DOXYGEN__)
static inline void _delay_loop_1(uint8_t __count) __attribute__((always_inline));
static inline void _delay_loop_2(uint16_t __count) __attribute__((always_inline));
#endif

/** \file */
/** \defgroup util_delay_basic <util/delay_basic.h>: Basic busy-wait delay loops
\code
#include <util/delay_basic.h>
\endcode

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.

*/

/** \ingroup util_delay_basic

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 util_delay_basic

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)
);
}

#endif /* _UTIL_DELAY_BASIC_H_ */