close #6

README.md

@@ -26,6 +26,8 @@ Development, not yet functional
 | 0010   | 0x2          | Request receiver configuration | TX -> RX |
 | 0011   | 0x3          | Receiver configuration | RX -> TX |
 | 0100   | 0x4          | Set receiver configuration | TX -> RX |
+| 0101   | 0x5          | PING frame | TX -> RX |
+| 0110   | 0x6          | PONG frame | RX -> TX |
 
 ### `RC_DATA` frame format
 
@@ -47,3 +49,9 @@ Total length of `RC_DATA` payload is 9 bytes
 | 4     | RX analog input 1 sent in 0,1V        |
 | 5     | RX analog input 2 sent in 0,1V        |
 | 6     | Last received packet ID               |
+
+### `PING` and `PONG` frames
+
+`PING` and `PONG` frames are to determine packet roundrip between **TX** and **RX** module.
+**TX** sends `PING` frame with curent `micros`. If **RX** receives `PING` frame, it respons
+its payload as `PONG` frame. 

crossbow.ino

@@ -5,7 +5,7 @@
 // #define DEVICE_MODE_RX
 
 #define DEBUG_SERIAL
-#define DEBUG_LED
+// #define DEBUG_LED
 // #define WAIT_FOR_SERIAL
 
 #include <LoRa.h>
@@ -178,6 +178,11 @@ if (!LoRa.begin(868E6))
     #endif
         while (true);
     }
+
+    LoRa.setSignalBandwidth(250E3);
+    LoRa.setSpreadingFactor(7);
+    LoRa.setCodingRate4(5);
+
 #ifdef DEBUG_SERIAL
     Serial.println("Init done");
 #endif
@@ -302,7 +307,37 @@ void loop(void)
     uint32_t currentMillis = millis();
     bool transmitPayload = false;
 
+    if (
+        qsp.forcePongFrame && 
+        !transmitPayload && 
+        qsp.protocolState == QSP_STATE_IDLE
+    )
+    {
+        qsp.forcePongFrame = false;
+        qsp.lastFrameTransmitedAt[QSP_FRAME_PONG] = currentMillis;
+        qsp.frameToSend = QSP_FRAME_PONG;
+        transmitPayload = true;
+    }
+
+
 #ifdef DEVICE_MODE_TX
+
+    //PING frame
+    if (
+        currentMillis - qsp.lastFrameTransmitedAt[QSP_FRAME_PING] > TX_PING_RATE && 
+        !transmitPayload && 
+        qsp.protocolState == QSP_STATE_IDLE
+    )
+    {
+        qsp.lastFrameTransmitedAt[QSP_FRAME_PING] = currentMillis;
+
+        qspClearPayload(&qsp);
+        encodePingPayload(&qsp, micros());
+        qsp.frameToSend = QSP_FRAME_PING;
+        
+        transmitPayload = true;
+    }
+
     /*
      * RC_DATA QSP frame
      */
@@ -355,14 +390,12 @@ void loop(void)
 
     if (qsp.canTransmit && transmitPayload)
     {
-        transmitPayload = false;
-        
         radioPacketStart();
         qspEncodeFrame(&qsp);
         radioPacketEnd();
 
     #ifdef DEBUG_SERIAL
-        Serial.print("Packet frame ");
+        Serial.print("Frame ");
         Serial.print(qsp.frameToSend);
         Serial.println(" sent");
     #endif
@@ -376,6 +409,7 @@ void loop(void)
         delay(10);
         digitalWrite(LED_BUILTIN, LOW);
     #endif
+        transmitPayload = false;
     }
 
     /*

qsp.cpp

@@ -248,6 +248,25 @@ void qspDecodeIncomingFrame(QspConfiguration_t *qsp, uint8_t incomingByte, int p
                     }
                     break;
 
+                case QSP_FRAME_PING:
+                    qsp->forcePongFrame = true;
+                    break;
+
+                case QSP_FRAME_PONG:
+                    if (qsp->debugConfig & DEBUG_FLAG_SERIAL) {
+
+                        uint32_t incoming = 0;
+
+                        incoming = qsp->payload[0];
+                        incoming += (uint32_t) qsp->payload[1] << 8;
+                        incoming += (uint32_t) qsp->payload[2] << 16;
+                        incoming += (uint32_t) qsp->payload[3] << 24;
+
+                        Serial.print("Rountrip: ");
+                        Serial.println((micros() - incoming) / 1000);
+                    }
+                    break;
+
                 default:
                     //Unknown frame
                     //TODO do something in this case
@@ -294,3 +313,12 @@ void qspEncodeFrame(QspConfiguration_t *qsp) {
     //Finally write CRC
     qsp->hardwareWriteFunction(qsp->crc, qsp);
 }
+
+void encodePingPayload(QspConfiguration_t *qsp, uint32_t currentMicros) {
+    qsp->payload[0] = currentMicros & 255;
+    qsp->payload[1] = (currentMicros >> 8) & 255;
+    qsp->payload[2] = (currentMicros >> 16) & 255;
+    qsp->payload[3] = (currentMicros >> 24) & 255;
+
+    qsp->payloadLength = 9;
+}

qsp.h

@@ -13,3 +13,5 @@ uint8_t qspGetPacketId(void);
 void qspDecodeIncomingFrame(QspConfiguration_t *qsp, uint8_t incomingByte, int ppm[], RxDeviceState_t *rxDeviceState);
 void qspClearPayload(QspConfiguration_t *qsp);
 void qspEncodeFrame(QspConfiguration_t *qsp);
+
+void encodePingPayload(QspConfiguration_t *qsp, uint32_t currentMicros);

variables.h

@@ -10,6 +10,8 @@
 #define TX_RC_FRAME_RATE 1000 //ms
 #define RX_FAILSAFE_DELAY (TX_RC_FRAME_RATE * 4)
 
+#define TX_PING_RATE 2000 
+
 #define CHANNEL_ID 0x01
 #define QSP_PREAMBLE 0x51
 #define QSP_PAYLOAD_LENGTH 32
@@ -19,7 +21,9 @@
 #define QSP_FRAME_GET_RX_CONFIG 0x2
 #define QSP_FRAME_RX_CONFIG 0x3
 #define QSP_FRAME_SET_RX_CONFIG 0x4
-#define QSP_FRAME_COUNT 0x5
+#define QSP_FRAME_PING 0x5
+#define QSP_FRAME_PONG 0x6
+#define QSP_FRAME_COUNT 0x7
 
 #define RX_ADC_PIN_1 A0
 #define RX_ADC_PIN_2 A1
@@ -66,6 +70,7 @@ struct QspConfiguration_t {
     void (* hardwareWriteFunction)(uint8_t, QspConfiguration_t*);
     uint8_t lastReceivedPacketId = 0;
     bool canTransmit = false;
+    bool forcePongFrame = false;
     uint8_t debugConfig = 0;
 };