From cbae234327a3cc2a50e8528d9d5c45aab35d0b3e Mon Sep 17 00:00:00 2001
From: Ian Gulliver <flamingcow@gmail.com>
Date: Mon, 15 Feb 2016 22:01:32 +0000
Subject: [PATCH] MLAT (width and frequency) and RSSI (width) scaling working.

---
 airspy_adsb.c |  7 +++----
 common.c      | 28 ++++++++++++++++++++++++++++
 common.h      | 17 +++++++++++++++--
 3 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/airspy_adsb.c b/airspy_adsb.c
index 81d8e97..71969fd 100644
--- a/airspy_adsb.c
+++ b/airspy_adsb.c
@@ -7,8 +7,7 @@
 #include "airspy_adsb.h"
 
 struct airspy_adsb_parser_state {
-	uint64_t mlat_timestamp_last;
-	uint64_t mlat_timestamp_generation;
+	struct mlat_state mlat_state;
 };
 
 static bool airspy_adsb_parse_common(char *, struct packet *, struct airspy_adsb_parser_state *);
@@ -60,7 +59,7 @@ static bool airspy_adsb_parse_common(char *in, struct packet *packet, struct air
 		return false;
 	}
 	uint16_t mlat_mhz = 2 * hex_to_int(&in[9], 1);
-	packet->mlat_timestamp = hex_to_int(in, 4) * (MLAT_MHZ / mlat_mhz);
-	packet->rssi = hex_to_int(&in[12], 2) * (RSSI_MAX / UINT16_MAX);
+	packet->mlat_timestamp = mlat_timestamp_scale_in(hex_to_int(in, 4), UINT32_MAX, mlat_mhz, &state->mlat_state);
+	packet->rssi = rssi_scale_in(hex_to_int(&in[12], 2), UINT16_MAX);
 	return true;
 }
diff --git a/common.c b/common.c
index d33945d..2989fef 100644
--- a/common.c
+++ b/common.c
@@ -7,6 +7,10 @@
 #include "common.h"
 
 
+#define MLAT_MHZ 120
+#define RSSI_MAX UINT32_MAX
+
+
 void buf_init(struct buf *buf) {
 	buf->start = 0;
 	buf->length = 0;
@@ -40,6 +44,30 @@ void buf_consume(struct buf *buf, size_t length) {
 }
 
 
+uint64_t mlat_timestamp_scale_mhz_in(uint64_t timestamp, uint32_t mhz) {
+	return timestamp * (MLAT_MHZ / mhz);
+}
+
+uint64_t mlat_timestamp_scale_width_in(uint64_t timestamp, uint64_t max, struct mlat_state *state) {
+	if (timestamp < state->timestamp_last) {
+		// Counter reset
+		state->timestamp_generation += max;
+	}
+
+	state->timestamp_last = timestamp;
+	return state->timestamp_generation + timestamp;
+}
+
+uint64_t mlat_timestamp_scale_in(uint64_t timestamp, uint64_t max, uint16_t mhz, struct mlat_state *state) {
+	return mlat_timestamp_scale_mhz_in(mlat_timestamp_scale_width_in(timestamp, max, state), mhz);
+}
+
+
+uint32_t rssi_scale_in(uint32_t value, uint32_t max) {
+	return value * (RSSI_MAX / max);
+}
+
+
 static uint8_t hex_table[256] = {0};
 
 void hex_init() {
diff --git a/common.h b/common.h
index 7ea384c..ec7c7be 100644
--- a/common.h
+++ b/common.h
@@ -34,8 +34,6 @@ void buf_consume(struct buf *, size_t);
 
 //////// packet
 
-#define MLAT_MHZ 120
-#define RSSI_MAX UINT32_MAX
 #define DATA_LEN_MAX 14
 struct packet {
 	enum {
@@ -49,6 +47,21 @@ struct packet {
 };
 
 
+//////// mlat
+
+struct mlat_state {
+	uint64_t timestamp_last;
+	uint64_t timestamp_generation;
+};
+
+uint64_t mlat_timestamp_scale_in(uint64_t, uint64_t, uint16_t, struct mlat_state *);
+
+
+//////// rssi
+
+uint32_t rssi_scale_in(uint32_t, uint32_t);
+
+
 //////// hex
 
 void hex_init();