0,0 → 1,144 |
/*####################################################################################### |
Decodieren eines RC Summen Signals |
#######################################################################################*/ |
// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
// + Copyright (c) 04.2007 Holger Buss |
// + only for non-profit use |
// + www.MikroKopter.com |
// + see the File "License.txt" for further Informations |
// ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
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#include <stdlib.h> |
#include <avr/io.h> |
#include <avr/interrupt.h> |
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#include "rc.h" |
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volatile int16_t PPM_in[11]; |
volatile int16_t PPM_diff[11]; |
volatile uint8_t NewPpmData = 1; |
volatile uint8_t SenderOkay = 0; |
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/***************************************************************/ |
/* 16bit timer 1 is used to decode the PPM-Signal */ |
/***************************************************************/ |
void rc_sum_init (void) |
{ |
uint8_t sreg = SREG; |
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// disable all interrupts before reconfiguration |
cli(); |
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// PPM-signal is connected to the Input Capture Pin (PD6) of timer 1 |
DDRD &= ~(1<<DDD6); |
PORTD |= (1<<PORTD6); |
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// Channel 5,6,7 is decoded to servo signals at pin PD5 (J3), PD4(J4), PD3(J5) |
// set as output |
DDRD |= (1<<DDD5)|(1<<DDD4)|(1<<DDD3); |
// low level |
PORTD &= ~((1<<PORTD5)|(1<<PORTD4)|(1<<PORTD3)); |
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// Timer/Counter1 Control Register A, B, C |
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// Normal Mode (bits: WGM13=0, WGM12=0, WGM11=0, WGM10=0) |
// Compare output pin A & B is disabled (bits: COM1A1=0, COM1A0=0, COM1B1=0, COM1B0=0) |
// Set clock source to SYSCLK/64 (bit: CS12=0, CS11=1, CS10=1) |
// Enable input capture noise cancler (bit: ICNC1=1) |
// Trigger on positive edge of the input capture pin (bit: ICES1=1), |
// Therefore the counter incremets at a clock of 20 MHz/64 = 312.5 kHz or 3.2µs |
// The longest period is 0xFFFF / 312.5 kHz = 0.209712 s. |
TCCR1A &= ~((1<<COM1A1)|(1<<COM1A0)|(1<<COM1B1)|(1<<COM1B0)|(1<<WGM11)|(1<<WGM10)); |
TCCR1B &= ~((1<<WGM13)|(1<<WGM12)|(1<<CS12)); |
TCCR1B |= (1<<CS11)|(1<<CS10)|(1<<ICES1)|(1<<ICNC1); |
TCCR1C &= ~((1<<FOC1A)|(1<<FOC1B)); |
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// Timer/Counter1 Interrupt Mask Register |
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// Enable Input Capture Interrupt (bit: ICIE1=1) |
// Disable Output Compare A & B Match Interrupts (bit: OCIE1B=0, OICIE1A=0) |
// Disable Overflow Interrupt (bit: TOIE1=0) |
TIMSK1 &= ~((1<<OCIE1B)|(1<<OCIE1A)|(1<<TOIE1)); |
TIMSK1 |= (1<<ICIE1); |
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SREG = sreg; |
} |
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/********************************************************************/ |
/* Every time a positive edge is detected at PD6 */ |
/********************************************************************/ |
/* |
The PPM-Frame length is 22.5 ms. |
Channel high pulse width range is 0.7 ms to 1.7 ms completed by an 0.3 ms low pulse. |
The mininimum time delay of two events coding a channel is ( 0.7 + 0.3) ms = 1 ms. |
The maximum time delay of two events coding a chanel is ( 1.7 + 0.3) ms = 2 ms. |
The minimum duration of all channels at minimum value is 8 * 1 ms = 8 ms. |
The maximum duration of all channels at maximum value is 8 * 2 ms = 16 ms. |
The remaining time of (22.5 - 8 ms) ms = 14.5 ms to (22.5 - 16 ms) ms = 6.5 ms is |
the syncronization gap. |
*/ |
ISR(TIMER1_CAPT_vect) // typical rate of 1 ms to 2 ms |
{ |
static uint16_t oldICR1 = 0; |
int16_t signal = 0, tmp; |
static int16_t index; |
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// 16bit Input Capture Register ICR1 contains the timer value TCNT1 |
// at the time the edge was detected |
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// calculate the time delay to the previous event time which is stored in oldICR1 |
signal = (uint16_t) ICR1 - oldICR1; |
oldICR1 = ICR1; |
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//sync gap? (3.52 ms < signal < 25.6 ms) |
if((signal > 1100) && (signal < 8000)) |
{ |
// if a sync gap happens and there where at least 4 channels decoded before |
// then the NewPpmData flag is reset indicating valid data in the PPM_in[] array. |
if(index >= 4) NewPpmData = 0; // Null means NewData |
// synchronize channel index |
index = 1; |
} |
else // within the PPM frame |
{ |
if(index < 10) // channel limit is 9 because of the frame length of 22.5 ms |
{ |
// check for valid signal length (0.8 ms < signal < 2.1984 ms) |
// signal range is from 1.0ms/3.2us = 312 to 2.0ms/3.2us = 625 |
if((signal > 250) && (signal < 687)) |
{ |
// shift signal to zero symmetric range -154 to 159 |
signal -= 466; // offset of 1.4912 ms ??? (469 * 3.2µs = 1.5008 ms) |
// check for stable signal |
// the deviation of the current signal level from the average must be less than 6 (aprox. 1%) |
if(abs(signal - PPM_in[index]) < 6) |
{ |
// a good signal condition increases SenderOkay by 10 |
// SignalOkay is decremented every 2 ms in main.c |
// this variable is a level for the average rate of a noiseless rc signal |
if(SenderOkay < 200) SenderOkay += 10; |
} |
// calculate exponential history for signal |
tmp = (3 * (PPM_in[index]) + signal) / 4; |
if(tmp > signal+1) tmp--; else |
if(tmp < signal-1) tmp++; |
// calculate signal difference on good signal level |
if(SenderOkay >= 195) PPM_diff[index] = ((tmp - PPM_in[index]) / 3) * 3; // cut off lower 3 bit for nois reduction |
else PPM_diff[index] = 0; |
PPM_in[index] = tmp; // update channel value |
} |
index++; // next channel |
// demux sum signal for channels 5 to 7 to J3, J4, J5 |
if(index == 5) PORTD |= (1<<PORTD5); else PORTD &= ~(1<<PORTD5); |
if(index == 6) PORTD |= (1<<PORTD4); else PORTD &= ~(1<<PORTD4); |
if(index == 7) PORTD |= (1<<PORTD3); else PORTD &= ~(1<<PORTD3); |
} |
} |
} |
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