AP_GPS: tidy pre_arm_checks

libraries/AP_GPS/AP_GPS.cpp

@@ -1808,18 +1808,17 @@ bool AP_GPS::prepare_for_arming(void) {
     return all_passed;
 }
 
-bool AP_GPS::backends_healthy(char failure_msg[], uint16_t failure_msg_len) {
+bool AP_GPS::pre_arm_checks(char failure_msg[], uint16_t failure_msg_len)
-    for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
+{
+    // the DroneCAN class has additional checks for DroneCAN-specific
+    // parameters:
 #if AP_GPS_DRONECAN_ENABLED
-        const auto type = params[i].type;
+    if (!AP_GPS_DroneCAN::inter_instance_pre_arm_checks(failure_msg, failure_msg_len)) {
-        if (type == GPS_TYPE_UAVCAN ||
+        return false;
-            type == GPS_TYPE_UAVCAN_RTK_BASE ||
+    }
-            type == GPS_TYPE_UAVCAN_RTK_ROVER) {
-            if (!AP_GPS_DroneCAN::backends_healthy(failure_msg, failure_msg_len)) {
-                return false;
-            }
-        }
 #endif
+
+    for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
         if (is_rtk_rover(i)) {
             if (AP_HAL::millis() - state[i].gps_yaw_time_ms > 15000) {
                 hal.util->snprintf(failure_msg, failure_msg_len, "GPS[%u] yaw not available", unsigned(i+1));

libraries/AP_GPS/AP_GPS.h

@@ -551,9 +551,10 @@ public:
     // returns true if all GPS instances have passed all final arming checks/state changes
     bool prepare_for_arming(void);
 
-    // returns true if all GPS backend drivers haven't seen any failure
+    // returns true if all GPS backend drivers are OK with the concept
-    // this is for backends to be able to spout pre arm error messages
+    // of the vehicle arming.  this is for backends to be able to
-    bool backends_healthy(char failure_msg[], uint16_t failure_msg_len);
+    // spout pre arm error messages
+    bool pre_arm_checks(char failure_msg[], uint16_t failure_msg_len);
 
     // returns false if any GPS drivers are not performing their logging appropriately
     bool logging_failed(void) const;

libraries/AP_GPS/AP_GPS_DroneCAN.cpp

@@ -225,8 +225,24 @@ AP_GPS_Backend* AP_GPS_DroneCAN::probe(AP_GPS &_gps, AP_GPS::GPS_State &_state)
     return backend;
 }
 
-bool AP_GPS_DroneCAN::backends_healthy(char failure_msg[], uint16_t failure_msg_len)
+bool AP_GPS_DroneCAN::inter_instance_pre_arm_checks(char failure_msg[], uint16_t failure_msg_len)
 {
+    // only do these checks if there is at least one DroneCAN GPS:
+    bool found_uavan_type = false;
+    for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
+        const auto type = AP::gps().params[i].type;
+        if (type != AP_GPS::GPS_TYPE_UAVCAN &&
+            type != AP_GPS::GPS_TYPE_UAVCAN_RTK_BASE &&
+            type != AP_GPS::GPS_TYPE_UAVCAN_RTK_ROVER) {
+            continue;
+        }
+        found_uavan_type = true;
+   }
+    if (!found_uavan_type) {
+        return true;
+    }
+
+    // lint parameters and detected node IDs:
     for (uint8_t i = 0; i < GPS_MAX_RECEIVERS; i++) {
         const auto &params_i = AP::gps().params[i];
         bool overriden_node_found = false;

libraries/AP_GPS/AP_GPS_DroneCAN.h

@@ -56,7 +56,7 @@ public:
     static void handle_moving_baseline_msg_trampoline(AP_DroneCAN *ap_dronecan, const CanardRxTransfer& transfer, const ardupilot_gnss_MovingBaselineData& msg);
     static void handle_relposheading_msg_trampoline(AP_DroneCAN *ap_dronecan, const CanardRxTransfer& transfer, const ardupilot_gnss_RelPosHeading& msg);
 #endif
-    static bool backends_healthy(char failure_msg[], uint16_t failure_msg_len);
+    static bool inter_instance_pre_arm_checks(char failure_msg[], uint16_t failure_msg_len);
     void inject_data(const uint8_t *data, uint16_t len) override;
 
     bool get_error_codes(uint32_t &error_codes) const override { error_codes = error_code; return seen_status; };