ArduPPM(experimental): Active input channel detection during init

Tools/ArduPPM/WorkBasket/Experimental/PPM_Encoder.h

@@ -73,6 +73,7 @@
 
 // 22-11-2012
 // V2.3.11 - Very experimental test forcing throttle fail-safe (RTL) on single channel loss. !DO NOT RELEASE TO PUBLIC!
+//              - Test for active input channels during init
 
 // -------------------------------------------------------------
 
@@ -562,7 +563,7 @@ CHECK_PINS_LOOP: // Input servo pin check loop
             wdt_reset(); 
 
             // Channel has received a valid signal, so it must be connected
-			servo_input_connected [ ppm_channel ] = true;
+            // servo_input_connected [ ppm_channel ] = true; // Removed - Check performed during init
             
             // Check for forced throttle fail-safe
             if( throttle_failsafe_force && ppm_channel == 5 )
@@ -607,7 +608,7 @@ CHECK_PINS_NEXT:
     
     // Check channel and process if needed
     //if( servo_channel < SERVO_CHANNELS ) goto CHECK_PINS_LOOP;
-	if( servo_pin ) goto CHECK_PINS_LOOP; // Bitshift wraps to zero (false)
+    if( servo_pin ) goto CHECK_PINS_LOOP; // Bit shifts to zero when all pins have been checked
     
     goto CHECK_PINS_DONE;
 
@@ -823,28 +824,119 @@ void ppm_encoder_init( void )
     }
 #endif
 
-    // SERVO/PPM INPUT - PIN CHANGE INTERRUPT
-    // ------------------------------------------------------------------------------
-    if( servo_input_mode == SERVO_PWM_MODE )
-    {
-        // Set servo input interrupt pin mask to all 8 servo input channels
-        SERVO_INT_MASK = 0xFF;
-    }
-
+     // PPM PASS-THROUGH MODE
     if( servo_input_mode == PPM_PASSTROUGH_MODE )
     {
         // Set servo input interrupt pin mask to servo input channel 1
         SERVO_INT_MASK = 0x01;
     }
 
+    // SERVO PWM INPUT MODE
+    // ------------------------------------------------------------------------------
+    if( servo_input_mode == SERVO_PWM_MODE )
+    {
+        // CHECK FOR ACTIVE INPUT CHANNELS
+        // ------------------------------------------------------------------------------    
+        // This will poll the input pins looking for pin level changes, and mark the inputs with active signal connections
+        
+        uint16_t input_channel_count[ SERVO_CHANNELS ];
+        uint8_t input_current; // Input pin level mask
+        uint8_t input_previous; // Input pin level mask
+        uint8_t input_int_mask; // Active input pin interupt mask
+        
+    INPUT_ACTIVE_CHANNEL_CHECK:
+
+        // ~100khz timed polling of input pins for ~0.5sec duration (1us = 16 clocks)
+        for( uint16_t t = 0; t < 50000; t++ ) // 10us * 1000ms * 0.5sec = 50000 delayed loops at 10us
+        {
+                // Get current input pin levels
+                input_current = SERVO_INPUT;
+                
+                // Check input pins against previous levels
+                uint8_t input_change = input_current ^ input_previous;
+                    
+                // Do we need to check for changes?
+                if( input_change )
+                {
+                    // Check for change on all input pins
+                    uint8_t input_pin = 1;
+                    uint8_t input_channel = 0;
+                    
+                    do
+                    {
+                        // Check for change on current input pin
+                        if( input_change & input_pin )
+                        {
+                            // Pin has changed, count it
+                            input_channel_count[ input_channel ]++;
+                        }
+                    
+                        // Select next pin
+                        input_pin <<= 1;
+                        
+                        // Select next channel
+                        input_channel++;
+
+                    } while ( input_channel < SERVO_CHANNELS );
+                
+                    // Store checked input pin levels
+                    input_previous = input_current;
+                }
+                
+                // Delay the next input level check
+                _delay_us( 10 );
+        
+        }
+
+        // Check input_channel_count[..] to see if channels are active.
+        for( uint8_t input_channel = 0; input_channel < SERVO_CHANNELS; input_channel++ )
+        {
+            // Is current channel active?
+            if( input_channel_count[ input_channel ] > 20 ) // 0.5sec * 40hz * 2 = 40 pulse edges - 50% margin = 20 level changes
+            {
+                // Set active channel in servo_input_connected[..]
+                servo_input_connected[ (input_channel << 1) + 1 ] = true;    
+                
+                // Set interupt pin mask for active channel
+                input_int_mask |= 1 << input_channel;
+
+            }
+        }
+        
+        // if no active input channels are found, then re-check until found (might be caused by delayed receiver startup) 
+        // Do not perform re-check if there was a brown-out reset
+        if( input_int_mask > 0 && !brownout_reset  )
+        {
+            // Re-check active input channels
+            goto INPUT_ACTIVE_CHANNEL_CHECK;
+        }
+        
+        // Set servo input interrupt pin mask
+        // Set to all input channel for safety in case of brown-out reset
+        if( brownout_reset)
+        {
+            // Interrupt on all input pins
+            SERVO_INT_MASK = 0xFF;
+        }
+        else
+        {
+            // Interrupt only on active input pins
+            SERVO_INT_MASK = input_int_mask;
+        }
+    }
+
+    
     // Enable servo input interrupt
     PCICR |= (1 << SERVO_INT_ENABLE);
 
-    // PPM OUTPUT PIN
+    // PPM OUTPUT
     // ------------------------------------------------------------------------------
+    // PPM generator (PWM output timer/counter) is started either by pin change interrupt or by watchdog interrupt
+
     // Set PPM pin to output
     PPM_DDR |= (1 << PPM_OUTPUT_PIN);
 
+    
     // ------------------------------------------------------------------------------
     // Enable watchdog interrupt mode
     // ------------------------------------------------------------------------------