From 06fb69d30467df4e99cfd0c92900f226e574d34f Mon Sep 17 00:00:00 2001
From: Verkehrsrot <cyberman@obh.snafu.de>
Date: Sat, 5 Oct 2019 13:15:45 +0200
Subject: [PATCH] timesync.cpp cleanups

---
 src/timesync.cpp | 42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

diff --git a/src/timesync.cpp b/src/timesync.cpp
index a50d7ca1..e0c0dbb3 100644
--- a/src/timesync.cpp
+++ b/src/timesync.cpp
@@ -94,7 +94,7 @@ void process_timesync_req(void *taskparameter) {
 
       // wrap around seqNo, keeping it in time port range
       time_sync_seqNo++;
-      if(time_sync_seqNo > TIMEREQUEST_MAX_SEQNO) {
+      if (time_sync_seqNo > TIMEREQUEST_MAX_SEQNO) {
         time_sync_seqNo = 0;
       }
 
@@ -154,18 +154,30 @@ void store_time_sync_req(uint32_t timestamp) {
            timestamp % 1000);
 }
 
-// process timeserver timestamp answer, called from lorawan.cpp
+// process timeserver timestamp answer, called by myRxCallback() in lorawan.cpp
 int recv_timesync_ans(const uint8_t buf[], const uint8_t buf_len) {
-  uint8_t seq_no = buf[0];
-  buf++;
+
+  /*
+  parse 7 byte timesync_answer:
+
+  byte    meaning
+  1       sequence number (taken from node's time_sync_req)
+  2       timezone in 15 minutes steps
+  3..6    current second (from epoch time 1970)
+  7       1/250ths fractions of current second
+  */
 
   // if no timesync handshake is pending then exit
   if (!timeSyncPending)
     return 0; // failure
 
+  // extract 1 byte timerequest sequence number from buffer
+  uint8_t seq_no = buf[0];
+  buf++;
+
   // if no time is available or spurious buffer then exit
   if (buf_len != TIME_SYNC_FRAME_LENGTH) {
-    if (buf[0] == 0xff)
+    if (seq_no == 0xff)
       ESP_LOGI(TAG, "[%0.3f] Timeserver error: no confident time available",
                millis() / 1000.0);
     else
@@ -178,24 +190,26 @@ int recv_timesync_ans(const uint8_t buf[], const uint8_t buf_len) {
 
     uint8_t k = seq_no % TIME_SYNC_SAMPLES;
 
-    // the 5th byte contains the fractional seconds in 2^-8 second steps
-    // (= 1/250th sec), we convert this to ms
-    uint16_t timestamp_msec = 4 * buf[6];
-    // pointers to 4 bytes 4 bytes containing UTC seconds since unix epoch, msb
+    // pointers to 4 bytes containing UTC seconds since unix epoch, msb
     uint32_t timestamp_sec, *timestamp_ptr;
-    uint32_t timezone_sec;
 
-    // extract timezone from buffer (in 15min steps, one step being 15min * 60s = 900s)
-    timezone_sec = buf[0]*900;
+    // extract 1 byte timezone from buffer (one step being 15min * 60s = 900s)
+    uint32_t timezone_sec = buf[0] * 900;
     buf++;
 
-    // convert buffer to uint32_t, octet order is big endian
+    // extract 4 bytes timestamp from buffer
+    // and convert it to uint32_t, octet order is big endian
     timestamp_ptr = (uint32_t *)buf;
     // swap byte order from msb to lsb, note: this is platform dependent
     timestamp_sec = __builtin_bswap32(*timestamp_ptr);
+    buf += 4;
+    // extract 1 byte fractional seconds in 2^-8 second steps
+    // (= 1/250th sec), we convert this to ms
+    uint16_t timestamp_msec = 4 * buf[0];
 
     // construct the timepoint when message was seen on gateway
-    time_sync_rx[k] += seconds(timestamp_sec+timezone_sec) + milliseconds(timestamp_msec);
+    time_sync_rx[k] +=
+        seconds(timestamp_sec + timezone_sec) + milliseconds(timestamp_msec);
 
     // we guess timepoint is recent if it newer than code compile date
     if (timeIsValid(myClock::to_time_t(time_sync_rx[k]))) {