feat(pps_capture): allow selecting GPS receiver by device ID (#26719)

* feat(pps_capture): allow selecting GPS receiver by device ID

Add PPS_CAP_GPS_ID parameter to select which GPS receiver's data
is used for PPS timestamp correlation. Matches by device ID rather
than uORB instance index, which avoids dependence on instance ordering.

When set to 0 (default), uses the first available instance for
backward compatibility.

* docs(pps_capture): document PPS_CAP_GPS_ID for multi-GPS setups

* fix(pps_capture): use GPS_MAX_RECEIVERS constant and mark PPS_CAP_GPS_ID reboot-required

src/drivers/pps_capture/PPSCapture.cpp

@@ -48,6 +48,7 @@
 ModuleBase::Descriptor PPSCapture::desc{task_spawn, custom_command, print_usage};
 
 PPSCapture::PPSCapture() :
+	ModuleParams(nullptr),
 	ScheduledWorkItem(MODULE_NAME, px4::wq_configurations::hp_default)
 {
 	_pps_capture_pub.advertise();
@@ -117,9 +118,16 @@ void PPSCapture::Run()
 
 	sensor_gps_s sensor_gps;
 
-	if (_sensor_gps_sub.update(&sensor_gps)) {
-		_last_gps_utc_timestamp = sensor_gps.time_utc_usec;
-		_last_gps_timestamp = sensor_gps.timestamp;
+	const uint32_t gps_device_id = static_cast<uint32_t>(_param_pps_cap_gps_id.get());
+
+	for (auto &sub : _sensor_gps_subs) {
+		if (sub.update(&sensor_gps)) {
+			if (gps_device_id == 0 || sensor_gps.device_id == gps_device_id) {
+				_last_gps_utc_timestamp = sensor_gps.time_utc_usec;
+				_last_gps_timestamp = sensor_gps.timestamp;
+				break;
+			}
+		}
 	}
 
 	pps_capture_s pps_capture;

src/drivers/pps_capture/PPSCapture.hpp

@@ -36,15 +36,17 @@
 #include <drivers/drv_hrt.h>
 #include <px4_arch/micro_hal.h>
 #include <px4_platform_common/module.h>
+#include <px4_platform_common/module_params.h>
 #include <px4_platform_common/px4_work_queue/ScheduledWorkItem.hpp>
 #include <uORB/Publication.hpp>
 #include <uORB/Subscription.hpp>
+#include <uORB/SubscriptionMultiArray.hpp>
 #include <uORB/topics/pps_capture.h>
 #include <uORB/topics/sensor_gps.h>
 
 using namespace time_literals;
 
-class PPSCapture : public ModuleBase, public px4::ScheduledWorkItem
+class PPSCapture : public ModuleBase, public ModuleParams, public px4::ScheduledWorkItem
 {
 public:
 	static Descriptor desc;
@@ -71,16 +73,23 @@ public:
 private:
 	void Run() override;
 
+	static constexpr int GPS_MAX_RECEIVERS = 2;
+
 	int _channel{-1};
 	uint32_t _pps_capture_gpio{0};
-	uORB::Publication<pps_capture_s>	_pps_capture_pub{ORB_ID(pps_capture)};
-	uORB::Subscription								_sensor_gps_sub{ORB_ID(sensor_gps)};
-	orb_advert_t											_mavlink_log_pub{nullptr};
 
-	hrt_abstime _hrt_timestamp{0};
+	uORB::Publication<pps_capture_s> _pps_capture_pub{ORB_ID(pps_capture)};
+	uORB::SubscriptionMultiArray<sensor_gps_s, GPS_MAX_RECEIVERS> _sensor_gps_subs{ORB_ID::sensor_gps};
+	orb_advert_t _mavlink_log_pub{nullptr};
+
+	hrt_abstime	_hrt_timestamp{0};
 
 	hrt_abstime	_last_gps_timestamp{0};
-	uint64_t		_last_gps_utc_timestamp{0};
-	uint8_t			_pps_rate_exceeded_counter{0};
-	px4::atomic<bool>			_pps_rate_failure{false};
+	uint64_t _last_gps_utc_timestamp{0};
+	uint8_t _pps_rate_exceeded_counter{0};
+	px4::atomic<bool> _pps_rate_failure{false};
+
+	DEFINE_PARAMETERS(
+		(ParamInt<px4::params::PPS_CAP_GPS_ID>) _param_pps_cap_gps_id
+	)
 };

src/drivers/pps_capture/pps_capture_params.c

@@ -41,3 +41,19 @@
  * @reboot_required true
  */
 PARAM_DEFINE_INT32(PPS_CAP_ENABLE, 0);
+
+/**
+ * PPS capture GPS receiver device ID
+ *
+ * Device ID of the GPS receiver that emits the PPS signal captured on the
+ * configured PWM input pin. When set to 0 (default), the first available
+ * GPS instance is used.
+ *
+ * The device ID can be obtained from the sensor_gps publication
+ * (e.g. via listener sensor_gps).
+ *
+ * @group GPS
+ * @min 0
+ * @reboot_required true
+ */
+PARAM_DEFINE_INT32(PPS_CAP_GPS_ID, 0);