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//$Id: TransformCounterC.nc,v 1.6 2010-06-29 22:07:50 scipio Exp $
/* Copyright (c) 2000-2003 The Regents of the University of California.
* 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 holder 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 HOLDER 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.
*/
/**
* TransformCounterC decreases precision and/or widens an Counter.
*
* <p>See TEP102 for more details.
*
* @param to_precision_tag A type indicating the precision of the transformed
* Counter.
* @param to_size_type The type for the width of the transformed Counter.
* @param from_precision_tag A type indicating the precision of the original
* Counter.
* @param from_size_type The type for the width of the original Counter.
* @param bit_shift_right Original time units will be 2 to the power
* <code>bit_shift_right</code> larger than transformed time units.
* @param upper_count_type A type large enough to store the upper bits --
* those needed above from_size_type after its shift right to fill
* to_size_type.
*
* @author Cory Sharp <cssharp@eecs.berkeley.edu>
*/
generic module TransformCounterC(
typedef to_precision_tag,
typedef to_size_type @integer(),
typedef from_precision_tag,
typedef from_size_type @integer(),
uint8_t bit_shift_right,
typedef upper_count_type @integer()) @safe()
{
provides interface Counter<to_precision_tag,to_size_type> as Counter;
uses interface Counter<from_precision_tag,from_size_type> as CounterFrom;
}
implementation
{
upper_count_type m_upper;
enum
{
LOW_SHIFT_RIGHT = bit_shift_right,
HIGH_SHIFT_LEFT = 8*sizeof(from_size_type) - LOW_SHIFT_RIGHT,
NUM_UPPER_BITS = 8*sizeof(to_size_type) - 8*sizeof(from_size_type) + bit_shift_right,
// 1. hack to remove warning when NUM_UPPER_BITS == 8*sizeof(upper_count_type)
// 2. still provide warning if NUM_UPPER_BITS > 8*sizeof(upper_count_type)
// 3. and allow for the strange case of NUM_UPPER_BITS == 0
OVERFLOW_MASK = NUM_UPPER_BITS ? ((((upper_count_type)2) << (NUM_UPPER_BITS-1)) - 1) : 0,
};
async command to_size_type Counter.get()
{
to_size_type rv = 0;
atomic
{
upper_count_type high = m_upper;
from_size_type low = call CounterFrom.get();
if (call CounterFrom.isOverflowPending())
{
// If we signalled CounterFrom.overflow, that might trigger a
// Counter.overflow, which breaks atomicity. The right thing to do
// increment a cached version of high without overflow signals.
// m_upper will be handled normally as soon as the out-most atomic
// block is left unless Clear.clearOverflow is called in the interim.
// This is all together the expected behavior.
high++;
low = call CounterFrom.get();
}
{
to_size_type high_to = high;
to_size_type low_to = low >> LOW_SHIFT_RIGHT;
rv = (high_to << HIGH_SHIFT_LEFT) | low_to;
}
}
return rv;
}
// isOverflowPending only makes sense when it's already part of a larger
// async block, so there's no async inside the command itself, where it
// wouldn't do anything useful.
async command bool Counter.isOverflowPending()
{
return ((m_upper & OVERFLOW_MASK) == OVERFLOW_MASK)
&& call CounterFrom.isOverflowPending();
}
// clearOverflow also only makes sense inside a larger atomic block, but we
// include the inner atomic block to ensure consistent internal state just in
// case someone calls it non-atomically.
async command void Counter.clearOverflow()
{
atomic
{
if (call Counter.isOverflowPending())
{
m_upper++;
call CounterFrom.clearOverflow();
}
}
}
async event void CounterFrom.overflow()
{
atomic
{
m_upper++;
if ((m_upper & OVERFLOW_MASK) == 0)
signal Counter.overflow();
}
}
}
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