Initial implementation of downlink windows

src/ControlTasks/RadioControlTask.cpp

@@ -204,17 +204,24 @@ void RadioControlTask::execute()
 #endif
         init();
         if (sfr::radio::init_mode == sensor_init_mode_type::complete) {
-            sfr::radio::mode = radio_mode_type::waiting;
+            sfr::radio::mode = radio_mode_type::downlink;
             sfr::radio::listen_period_start = millis();
-            sfr::radio::downlink_period_start = millis();
+            downlinkSettings();
         }
         break;
     }
-    case radio_mode_type::waiting: {
+    case radio_mode_type::downlink: {
 #ifdef VERBOSE
-        Serial.println(F("Radio: Waiting State"));
+        Serial.println(F("Radio: Downlink State"));
 #endif
-        if (millis() - sfr::radio::listen_period_start >= sfr::radio::listen_period) {
+        // downlink when slot reached
+        if (!sfr::radio::downlinked_in_slot && millis() - sfr::radio::downlink_window_start >= constants::radio::transmit_slot_length * sfr::radio::downlink_slot) {
+            executeDownlink();
+            sfr::radio::downlinked_in_slot = true;
+        }
+
+        // go into listen mode if listen period reached
+        if (millis() - sfr::radio::listen_period_start >= constants::radio::listen_period) {
             sfr::radio::mode = radio_mode_type::listen;
             sfr::radio::command_wait_start = millis();
 
@@ -223,20 +230,10 @@ void RadioControlTask::execute()
 #endif
             // downlink with listen flag = true
             normalReportDownlink();
-        } else if (millis() - sfr::radio::downlink_period_start >= sfr::radio::downlink_period) {
-            sfr::radio::mode = radio_mode_type::downlink;
         }
-        break;
-    }
-    case radio_mode_type::downlink: {
-#ifdef VERBOSE
-        Serial.println(F("Radio: Downlink State"));
-#endif
-        bool transmit_success = executeDownlink();
-        sfr::radio::mode = radio_mode_type::waiting;
-        // reset downlink period if downlink successful
-        if (transmit_success) {
-            sfr::radio::downlink_period_start = millis();
+        // reset window and choose slot for next downlink
+        else if (millis() - sfr::radio::downlink_window_start >= sfr::radio::downlink_window_length) {
+            downlinkSettings();
         }
         break;
     }
@@ -247,27 +244,34 @@ void RadioControlTask::execute()
         // built in timeout is 100 LoRa symbols
         bool receive_success = receive();
         if (receive_success) {
-#ifdef VERBOSE
-            Serial.println(F("Receive Success"));
-#endif
             processUplink();
-        } else {
-#ifdef VERBOSE
-            Serial.println(F("Receive Failed"));
-#endif
         }
 
-        if (receive_success || millis() - sfr::radio::command_wait_start >= sfr::radio::command_wait_period) {
-            sfr::radio::mode = radio_mode_type::waiting;
+        if (receive_success || millis() - sfr::radio::command_wait_start >= constants::radio::command_wait_period) {
+            sfr::radio::mode = radio_mode_type::downlink;
             sfr::radio::listen_period_start = millis();
+            downlinkSettings();
         }
         break;
     }
     }
 }
 
+void RadioControlTask::downlinkSettings()
+{
+#ifdef VERBOSE
+    Serial.println(F("Downlink Window Start"));
+#endif
+    // Reset window start time and pick random slot
+    sfr::radio::downlink_window_start = millis();
+    int num_slots = (sfr::radio::downlink_window_length / constants::radio::transmit_slot_length) - 1;
+    sfr::radio::downlink_slot = random(0, num_slots + 1); // max is exclusive
+    sfr::radio::downlinked_in_slot = false;
+}
+
 bool RadioControlTask::executeDownlink()
 {
+    // Downlink callsign report once in a while
     if (millis() - sfr::radio::last_callsign_time < constants::radio::callsign_interval) {
         return normalReportDownlink();
     } else {
@@ -283,6 +287,7 @@ bool RadioControlTask::executeDownlink()
 
 bool RadioControlTask::normalReportDownlink()
 {
+    // see https://github.com/Alpha-CubeSat/oop-chipsat-code/wiki/2.-Telemetry for more info
     uint16_t lat = sfr::gps::latitude * 10;
     uint16_t lon = sfr::gps::longitude * 10;
     uint16_t alt = sfr::gps::altitude / 10;
@@ -328,17 +333,17 @@ uint8_t RadioControlTask::map_range(float value, int min_val, int max_val)
 
 void RadioControlTask::processUplink()
 {
-
+    // see https://github.com/Alpha-CubeSat/oop-chipsat-code/wiki/3.-Commands for more info
     switch (received[0]) {
     case constants::opcodes::no_op: // No-Op
 #ifdef VERBOSE
         Serial.println(F("No-Op Command"));
 #endif
         sfr::radio::valid_uplinks++;
         break;
-    case constants::opcodes::change_downlink_period: { // Change downlink period
+    case constants::opcodes::change_downlink_window: { // Change downlink window length
         uint16_t combined = ((uint16_t)received[1] << 8) | received[2];
-        sfr::radio::downlink_period = combined * constants::time::one_second;
+        sfr::radio::downlink_window_length = combined * constants::time::one_second;
         sfr::radio::valid_uplinks++;
 #ifdef VERBOSE
         Serial.print(F("Change Downlink Command: "));

src/ControlTasks/RadioControlTask.hpp

@@ -15,6 +15,7 @@ class RadioControlTask
                              constants::radio::radio_rst_pin, constants::radio::radio_busy_pin);
     int16_t code;
     void init();
+    void downlinkSettings();
     bool transmit(uint8_t *packet, uint8_t size);
     bool receive();
     bool executeDownlink();

src/MainControlLoop.cpp

@@ -52,6 +52,9 @@ void MainControlLoop::execute()
     Serial.print("UTC Time: ");
     Serial.println(sfr::gps::utc_time);
 
+    Serial.print("Downlink Slot: ");
+    Serial.println(sfr::radio::downlink_slot);
+
 #endif
 
     temp_monitor.execute();

src/MainControlLoop.hpp

@@ -18,9 +18,6 @@ class MainControlLoop
 public:
     MainControlLoop();
     void execute();
-
-private:
-    float val;
 };
 
 #endif

src/Modes/radio_mode_type.enum

@@ -4,7 +4,6 @@
 enum class radio_mode_type : unsigned char
 {
     init = 0,
-    waiting,
     downlink,
     listen
 };

src/Monitors/GPSMonitor.cpp

@@ -8,7 +8,7 @@ GPSMonitor::GPSMonitor()
 {
 }
 
-void GPSMonitor::init() 
+void GPSMonitor::init()
 {
     digitalWrite(constants::gps::reset_pin, LOW);
     sfr::gps::on = true;
@@ -159,7 +159,7 @@ void GPSMonitor::execute()
             init();
         } else {
             return;
-        } 
+        }
     }
 
     // Check to see if anything is available in the serial receive buffer

src/constants.hpp

@@ -28,8 +28,12 @@ namespace constants {
         constexpr uint8_t id = 0;
 #endif
 
+        constexpr uint32_t listen_period = 30 * constants::time::one_second;
+        constexpr uint32_t command_wait_period = 30 * constants::time::one_second;
         constexpr uint32_t callsign_interval = 10 * constants::time::one_minute;
 
+        constexpr uint32_t transmit_slot_length = 2 * constants::time::one_second;
+
     } // namespace radio
     namespace imu {
         constexpr int gyro_min = -245;
@@ -58,7 +62,7 @@ namespace constants {
     }                                  // namespace gps
     namespace opcodes {
         constexpr uint8_t no_op = 0x00;
-        constexpr uint8_t change_downlink_period = 0x11;
+        constexpr uint8_t change_downlink_window = 0x11;
     } // namespace opcodes
 
 }; // namespace constants

src/main.cpp

@@ -13,6 +13,9 @@ void setup()
     pinMode(constants::gps::reset_pin, OUTPUT);
     digitalWrite(constants::gps::reset_pin, HIGH);
     sfr::gps::boot_time = millis();
+
+    // seed random number gen with noise from unconnected analog pin
+    randomSeed(analogRead(A0));
 }
 
 void loop()

src/sfr.cpp

@@ -31,14 +31,15 @@ namespace sfr {
         radio_mode_type mode = radio_mode_type::init;
         uint8_t start_progress = 0;
 
-        uint32_t downlink_period = 10 * constants::time::one_second;
-        uint32_t listen_period = 30 * constants::time::one_second;
-        uint32_t command_wait_period = 30 * constants::time::one_second;
-        uint32_t downlink_period_start;
+        uint32_t downlink_window_length = 10 * constants::time::one_second;
+        uint32_t downlink_window_start;
         uint32_t listen_period_start;
         uint32_t command_wait_start;
         uint32_t last_callsign_time;
 
+        uint8_t downlink_slot;
+        bool downlinked_in_slot = false;
+
         uint8_t valid_uplinks = 0;
         uint8_t invalid_uplinks = 0;
 

src/sfr.hpp

@@ -31,14 +31,15 @@ namespace sfr {
         extern uint8_t start_progress;
         extern radio_mode_type mode;
 
-        extern uint32_t downlink_period;
-        extern uint32_t listen_period;
-        extern uint32_t command_wait_period;
-        extern uint32_t downlink_period_start;
+        extern uint32_t downlink_window_length;
+        extern uint32_t downlink_window_start;
         extern uint32_t listen_period_start;
         extern uint32_t command_wait_start;
         extern uint32_t last_callsign_time;
 
+        extern uint8_t downlink_slot;
+        extern bool downlinked_in_slot;
+
         extern uint8_t valid_uplinks;
         extern uint8_t invalid_uplinks;