13
// channel sequence order
14
static const int channel_order_[] = { CHANNEL_ORDER };
16
// set to the time of the last pulse edges
17
static unsigned long new_pulse_up_[2] = { 0, 0 };
18
static unsigned long new_pulse_down_ = 0;
19
static char new_pulse_interrupt_;
22
// ISR to handle the PPM signals
23
inline void signal_handler( int interrupt, int pin )
25
// record rising/falling edge
26
if( digitalRead( pin ) )
27
new_pulse_up_[ interrupt ] = micros();
29
new_pulse_down_ = micros();
31
// record which interrupt just had a falling edge
32
new_pulse_interrupt_ = interrupt;
37
static void signal_handler_0()
39
signal_handler( 0, 2 );
43
static void signal_handler_1()
45
signal_handler( 1, 3 );
49
void Receiver::setup()
51
// set up an interrupts
52
attachInterrupt( 0, signal_handler_0, CHANGE );
53
attachInterrupt( 1, signal_handler_1, CHANGE );
54
digitalWrite( 2, LOW );
55
digitalWrite( 3, LOW );
59
bool Receiver::read_channels( int channel_values[] )
61
static unsigned long last_pulse_down = 0;
62
static int next_channel = 0;
64
// capture pulse values atomically
66
unsigned long pulse_up = new_pulse_up_[ (int)new_pulse_interrupt_ ];
67
unsigned long pulse_down = new_pulse_down_;
68
char new_pulse_interrupt = new_pulse_interrupt_;
71
// if the amount of time that has passed since the last falling edge is
72
// greater than the frame gap, reset the next channel so that we can start
75
new_pulse_interrupt == 1 &&
76
calculate_duration( pulse_down, micros() ) > MIN_FRAME_GAP_WIDTH )
78
// reset the next channel (which restarts reading them)
82
// check for a new complete pulse
83
if( pulse_down != last_pulse_down )
85
// are there still pulses to read?
86
if( next_channel < NUM_CHANNELS )
88
unsigned long duration =
89
calculate_duration( pulse_up, pulse_down );
91
// does this pulse look ok?
92
if( duration >= MIN_PULSE_WIDTH &&
93
duration <= MAX_PULSE_WIDTH )
95
// store channel value
96
int channel = channel_order_[ next_channel ] - 1;
97
channel_values[ channel ] = MAX_CHANNEL_VALUE *
98
( duration - MIN_PULSE_WIDTH ) /
99
( MAX_PULSE_WIDTH - MIN_PULSE_WIDTH );
105
// set invalid channel number (to indicate error)
106
next_channel = NUM_CHANNELS + 1;
110
last_pulse_down = pulse_down;
113
// if we've read a frame, invalidate the frame (so we don't report it a
114
// second time) and return true
115
if( next_channel == NUM_CHANNELS ) {