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//$Id: VirtualizeAlarmC.nc,v 1.8 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.
*/
/**
* VirtualizeAlarmC uses a single Alarm to create up to 255 virtual alarms.
* Note that a virtualized Alarm will have significantly more overhead than
* an Alarm built on a hardware compare register.
*
* @param precision_tag A type indicating the precision of the Alarm being
* virtualized.
* @param num_alarms Number of virtual alarms to create.
*
* @author Cory Sharp <cssharp@eecs.berkeley.edu>
*/
generic module VirtualizeAlarmC(typedef precision_tag, typedef size_type @integer(), int num_alarms)
{
provides interface Init;
provides interface Alarm<precision_tag,size_type> as Alarm[uint8_t id];
uses interface Alarm<precision_tag,size_type> as AlarmFrom;
}
implementation
{
enum {
NUM_ALARMS = num_alarms,
};
typedef struct {
size_type t0;
size_type dt;
} alarm_t;
// css 26 jul 2006: All computations with respect to the current time ("now")
// require that "now" is (non-strictly) monotonically increasing. Calling
// setNextAlarm within Alarm.start within Alarm.fired within signalAlarms
// breaks this monotonicity requirements when "now" is cached at the start of
// the function. Two ways around this: 1) refresh "now" each time it is
// used, or 2) use the is_signaling flag to prevent setNextAlarm from being
// called inside signalAlarms. The latter is generally more efficient by
// preventing redundant calls to setNextAlarm at the expense of an extra byte
// of RAM, so that's what the code does now. Update: option 2 is
// unacceptable because an Alarm.start could be called within some other
// Alarm.fired, which can break monotonicity in now.
// A struct of member variables so only one memset is called for init.
struct {
alarm_t alarm[NUM_ALARMS];
bool isset[NUM_ALARMS];
bool is_signaling;
} m;
command error_t Init.init() {
memset( &m, 0, sizeof(m) );
return SUCCESS;
}
void setNextAlarm() {
if( !m.is_signaling ) {
// css 25 jul 2006: To help prevent various problems with overflow, the
// elapsed time from t0 for a particular alarm is calculated as
// elapsed=now-t0 then dt-=elapsed and t0=now. However, this means that
// now must be a monotonically increasing value with each call to
// setNextAlarm -- overflow in now is okay, but passing in older values of
// now=t0 for some arbitrary t0 is not okay, which is what the previous
// version of setAlarm did.
const size_type now = call AlarmFrom.getNow();
const alarm_t* pEnd = m.alarm+NUM_ALARMS;
bool isset = FALSE;
alarm_t* p = m.alarm;
bool* pset = m.isset;
size_type dt = ((size_type)0)-((size_type)1);
for( ; p!=pEnd; p++,pset++ ) {
if( *pset ) {
size_type elapsed = now - p->t0;
if( p->dt <= elapsed ) {
p->t0 += p->dt;
p->dt = 0;
}
else {
p->t0 = now;
p->dt -= elapsed;
}
if( p->dt <= dt ) {
dt = p->dt;
isset = TRUE;
}
}
}
if( isset ) {
// css 25 jul 2006: If dt is big, then wait half of dt. This helps
// significantly reduce the chance of overflow in the elapsed calculation
// for the alarm. "big" is if the most signficant bit in dt is set.
if( dt & (((size_type)1) << (8*sizeof(size_type)-1)) )
dt >>= 1;
call AlarmFrom.startAt( now, dt );
}
else {
call AlarmFrom.stop();
}
}
}
void signalAlarms() {
uint8_t id;
m.is_signaling = TRUE;
for( id=0; id<NUM_ALARMS; id++ ) {
if( m.isset[id] ) {
//size_type elapsed = call AlarmFrom.getNow() - m.alarm[id].t0;
//if( m.alarm[id].dt <= elapsed ) {
size_type t0 = m.alarm[id].t0;
size_type elapsed = call AlarmFrom.getNow() - t0;
if( m.alarm[id].dt <= elapsed ) {
m.isset[id] = FALSE;
signal Alarm.fired[id]();
}
}
}
m.is_signaling = FALSE;
}
// basic interface
async command void Alarm.start[uint8_t id]( size_type dt ) {
call Alarm.startAt[id]( call AlarmFrom.getNow(), dt );
}
async command void Alarm.stop[uint8_t id]() {
atomic m.isset[id] = FALSE;
}
async event void AlarmFrom.fired() {
atomic {
signalAlarms();
setNextAlarm();
}
}
// extended interface
async command bool Alarm.isRunning[uint8_t id]() {
atomic return m.isset[id];
}
async command void Alarm.startAt[uint8_t id]( size_type t0, size_type dt ) {
atomic {
m.alarm[id].t0 = t0;
m.alarm[id].dt = dt;
m.isset[id] = TRUE;
setNextAlarm();
}
}
async command size_type Alarm.getNow[uint8_t id]() {
return call AlarmFrom.getNow();
}
async command size_type Alarm.getAlarm[uint8_t id]() {
atomic return m.alarm[id].t0 + m.alarm[id].dt;
}
default async event void Alarm.fired[uint8_t id]() {
}
}
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