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* Copyright (C) 2011 Tim Marston <edam@waxworlds.org>
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* This file is part of propeller-clock (hereafter referred to as "this
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* program"). See http://ed.am/software/arduino/propeller-clock for more
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published
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* by the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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/******************************************************************************
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For a schematic, see propeller-clock.sch.
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- a PC fan is wired up to the 12V supply.
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- the fan's SENSE (tachiometer) pin is connected to pin 2 on the
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- the pins 4 to 13 on the arduino should directly drive an LED (the
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LED on pin 4 is in the centre of the clock face and the LED on pin
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- if a longer hand (and a larger clock face) is desired, pin 4 can
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be used to indirectly drive (via a MOSFET) multiple LEDs which
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turn on and off in unison in the centre of the clock.
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- a button should be attached to pin 3 that grounds it when pressed.
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Implementation details:
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- the timing of the drawing of the clock face is recalculated with
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every rotation of the propeller (for maximum update speed).
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- pressing the button cycles between display modes
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- holding down the button for 2 seconds enters "set time" mode. In
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this mode, the fan must be held still and the LEDs will indicate
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what number is being entered for each time digit. Pressing the
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button increments the current digit. Holding it down moves to the
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next digit (or leaves "set time" mode when there are no more). In
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order, the digits (with accepted values) are: hours-tens (0 to 2),
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hours-ones (0 to 9), minutes-tens (0 to 5), minutes-ones (0 to 9).
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******************************************************************************/
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//_____________________________________________________________________________
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// when non-zero, the time (in microseconds) of a new fan pulse that
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// has just occurred, which means that segment drawing needs to be
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// set up an interrupt handler on pin 2 to nitice fan pulses
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attachInterrupt( 0, fanPulseHandler, RISING );
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digitalWrite( 2, HIGH );
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// set up output pins (4 to 13) for the led array
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for( int a = 4; a < 14; a++ )
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// when non-zero, the time (in microseconds) of a new fan pulse that has just
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// occurred, which means that segment drawing needs to be restarted
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static unsigned long new_pulse_at = 0;
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// the time (in microseconds) when the last fan pulse occurred
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static unsigned long last_pulse_at = 0;
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// duration (in microseconds) that a segment should be displayed
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static unsigned long segment_step = 0;
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// remainder after divisor and a tally of the remainders for each segment
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static unsigned long segment_step_sub_step = 0;
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static unsigned long segment_step_sub = 0;
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// flag to indicate that the drawing mode should be cycled to the next one
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static bool inc_draw_mode = false;
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// a bounce-managed button
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static Bounce button( 3, 5 );
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static int time_hours = 0;
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static int time_minutes = 0;
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static int time_seconds = 0;
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// number of segments in a full display (rotation) is 60 (one per
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// second) times the desired number of sub-divisions of a second
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#define NUM_SECOND_SEGMENTS 5
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#define NUM_SEGMENTS ( 60 * NUM_SECOND_SEGMENTS )
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//_____________________________________________________________________________
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// check for button presses
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// notice button presses
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if( button.risingEdge() )
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inc_draw_mode = true;
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// keep track of time
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// previous time and any carried-over milliseconds
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static unsigned long last_time = millis();
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static unsigned long carry = 0;
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// how many milliseonds have elapsed since we last checked?
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unsigned long next_time = millis();
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unsigned long delta = next_time - last_time + carry;
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// update the previous time and carried-over milliseconds
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last_time = next_time;
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carry = delta % 1000;
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// add the seconds that have passed to the time
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time_seconds += delta / 1000;
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while( time_seconds >= 60 ) {
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if( time_minutes >= 60 ) {
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if( time_hours >= 24 )
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// draw a segment for the test display
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void drawNextSegment_test( bool reset )
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// keep track of segment
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static unsigned int segment = 0;
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if( reset ) segment = 0;
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// turn on inside and outside LEDs
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digitalWrite( 4, HIGH );
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digitalWrite( 13, HIGH );
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// display segment number in binary across in the inside LEDs,
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// with the LED on pin 12 showing the least-significant bit
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for( int a = 0; a < 8; a++ )
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digitalWrite( 12 - a, ( ( segment >> a ) & 1 )? HIGH : LOW );
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// draw a segment for the time display
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void drawNextSegment_time( bool reset )
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static unsigned int second = 0;
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static unsigned int segment = 0;
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// handle display reset
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// what needs to be drawn?
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bool draw_tick = second % 5 == 0;
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bool draw_second = second == time_seconds;
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bool draw_minute = second == time_minute;
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bool draw_hour = second == time_hour;
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digitalWrite( 13, HIGH );
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digitalWrite( 12, draw_tick || draw_minute );
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for( int a = 10; a <= 11; a++ )
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digitalWrite( a, draw_minute || draw_second );
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for( int a = 4; a <= 9; a++ )
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digitalWrite( 10, draw_minute | draw_second || draw_hour );
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if( ++segment >= NUM_SECOND_SEGMENTS ) {
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// draw a display segment
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void drawNextSegment( bool reset )
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static int draw_mode = 0;
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// handle mode switch requests
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if( reset && inc_draw_mode ) {
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inc_draw_mode = false;
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switch( draw_mode ) {
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case 0: drawNextSegment_test( reset ); break;
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case 1: drawNextSegment_time( reset ); break;
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// calculate time constants when a new pulse has occurred
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void calculateSegmentTimes()
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// check for overflows, and only recalculate times if there isn't
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// one (if there is, we'll just go with the last pulse's times)
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if( new_pulse_at > last_pulse_at )
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// new segment stepping times
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unsigned long delta = new_pulse_at - last_pulse_at;
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segment_step = delta / NUM_SEGMENTS;
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segment_step_sub = 0;
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segment_step_sub_step = delta % NUM_SEGMENTS;
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// now we have dealt with this pulse, save the pulse time and
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// clear new_pulse_at, ready for the next pulse
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last_pulse_at = new_pulse_at;
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// wait until it is time to draw the next segment or a new pulse has
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void waitTillNextSegment( bool reset )
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static unsigned long end_time = 0;
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end_time = last_pulse_at;
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// work out the time that this segment should be displayed until
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end_time += segment_step;
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segment_step_sub += segment_step_sub_step;
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if( segment_step_sub >= NUM_SEGMENTS ) {
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segment_step_sub -= NUM_SEGMENTS;
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while( micros() < end_time && !new_pulse_at );
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// ISR to handle the pulses from the fan's tachiometer
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// interrupt handler to count the number of fan pulses
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void fanPulseHandler()
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// the fan actually sends two pulses per revolution. These pulses
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// may not be exactly evenly distributed around the rotation, so
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// we can't recalculate times on every pulse. Instead, we ignore
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// every other pulse so timings are based on a complete rotation.
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static bool ignore = true;
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// set a new pulse time
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new_pulse_at = micros();
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// ignore every other pulse
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static bool ignore = true;
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// set a new pulse time
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new_pulse_at = micros();
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// wait until it is time to draw the next segment or a new pulse has occurred
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void endOfSegmentDelay()
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// set up an interrupt handler on pin 2 to nitice fan pulses
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attachInterrupt( 0, fanPulseHandler, RISING );
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digitalWrite( 2, HIGH );
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// set up output pins (4 to 13) for the led array
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for( int a = 4; a < 14; a++ )
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pinMode( a, OUTPUT );
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// set up mode-switch button on pin 3
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Serial.begin( 9600 );
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while( micros() < next_segment_at && !new_pulse_at );
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// if there has been a new pulse, we'll be resetting the display
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bool reset = new_pulse_at? true : false;
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// only do this stuff at the start of a display cycle, to ensure
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// that no state changes mid-display
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// keep track of time
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drawNextSegment( reset );
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// do we need to recalculate segment times?
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calculateSegmentTimes();
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// wait till it's time to draw the next segment
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waitTillNextSegment( reset );
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unsigned long loop_start_time = micros();
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// wait till it's time to draw the next segment