Make GPS navigation epochs interrupt-coherent

Wait for every navigation-ready tracking channel in a GPS epoch, remove unlocked channels without a timeout, and keep late joins for the next epoch. Reset PLIC ownership during warm initialization and extend Linux synthetic, integrity, and fake-MMIO regression coverage.

soc/software/gps_system/header/gps/gps_ip_defines.h

@@ -19,7 +19,6 @@
 // |___|_|     |____/|_____|_|   |___|_| \_|_____|____/
 
 				#define MIN_NEEDED_SATELLITE     	4
-					#define GPS_INITIAL_SUBFRAME_MASK  ((1u << 1) | (1u << 2) | (1u << 3) | (1u << 4) | (1u << 5))
 				#define GPS_TRCK_UNLOCK_TIMEOUT_TICKS 500000000u
 				#define GPS_PRN_COUNT             32u
 				#define GPS_PRN_INVALID           0xffu
@@ -318,6 +317,7 @@
 		double        omgkdot;        // from subframe 3
 		double        idot;           // from subframe 3
 		unsigned char update;         // from subframe 3
+		bool          ephemeris_valid; // true only after a matching SF1/SF2/SF3 set is committed.
 		unsigned char sf4_data_id;    // from subframe 4 word 3.
 		unsigned char sf4_sv_id;      // page identifier encoded in subframe 4 word 3.
 		unsigned char sf4_page;       // decoded page number, or 0 if not mapped.

soc/software/gps_system/header/gps/gps_nav_epoch.h

@@ -0,0 +1,70 @@
+#ifndef GPS_NAV_EPOCH_H
+#define GPS_NAV_EPOCH_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+/*
+ * The current receiver exposes nine tracking channels.  Keep the epoch
+ * selector bounded so its exhaustive, allocation-free search has a fixed
+ * worst-case cost on the embedded target.
+ */
+#define GPS_NAV_EPOCH_MAX_CANDIDATES 9u
+
+typedef struct {
+	int week;
+	double tow_sec;
+	uint32_t raw_sample;
+} gps_nav_epoch_key_t;
+
+typedef struct {
+	uint32_t selected_mask;
+	unsigned int selected_count;
+	unsigned int reference_index;
+} gps_nav_epoch_selection_t;
+
+typedef struct {
+	uint64_t epoch_id;
+	uint32_t expected_mask;
+	uint32_t received_mask;
+	bool active;
+} gps_nav_epoch_assembly_t;
+
+typedef enum {
+	GPS_NAV_EPOCH_EVENT_INVALID = 0,
+	GPS_NAV_EPOCH_EVENT_ACCEPTED,
+	GPS_NAV_EPOCH_EVENT_DUPLICATE,
+	GPS_NAV_EPOCH_EVENT_STALE,
+	GPS_NAV_EPOCH_EVENT_FUTURE,
+	GPS_NAV_EPOCH_EVENT_COMPLETE
+} gps_nav_epoch_event_result_t;
+
+bool gps_nav_epoch_select(
+	const gps_nav_epoch_key_t candidates[GPS_NAV_EPOCH_MAX_CANDIDATES],
+	unsigned int candidate_count,
+	uint32_t sample_window,
+	double tow_tolerance_sec,
+	gps_nav_epoch_selection_t* selection);
+
+bool gps_nav_epoch_id(
+	int week,
+	double tow_sec,
+	unsigned int period_ms,
+	uint64_t* epoch_id);
+
+void gps_nav_epoch_assembly_reset(gps_nav_epoch_assembly_t* assembly);
+
+gps_nav_epoch_event_result_t gps_nav_epoch_assembly_push(
+	gps_nav_epoch_assembly_t* assembly,
+	uint64_t epoch_id,
+	unsigned int channel,
+	uint32_t ready_mask);
+
+bool gps_nav_epoch_assembly_remove_channel(
+	gps_nav_epoch_assembly_t* assembly,
+	unsigned int channel);
+
+bool gps_nav_epoch_assembly_complete(
+	const gps_nav_epoch_assembly_t* assembly);
+
+#endif

soc/software/gps_system/header/gps/linked_list.h

@@ -15,6 +15,7 @@ typedef struct gps_ephem_ll {
 	volatile bool gps_how_anchor_valid;
 	volatile uint32_t gps_nav_solve_sequence;
 	volatile uint32_t gps_nav_solve_consumed_sequence;
+	volatile gpstime_t gps_last_nav_solve_tow;
 	volatile uint32_t gps_last_nav_solve_abs_sample;
 	volatile double gps_last_nav_solve_corrected_abs_sample;
 	volatile uint64_t gps_last_nav_solve_local_ticks;