From 27c6e3d860aed41f6ed44997b1410b229f2bd53f Mon Sep 17 00:00:00 2001
From: Andreas Eversberg <jolly@eversberg.eu>
Date: Thu, 1 Dec 2016 17:59:08 +0100
Subject: [PATCH] C-Netz: Add code documentation...

---
 src/cnetz/cnetz.c        | 26 +++++++++++++++++++++++++-
 src/cnetz/fsk_fm_demod.c |  6 ++++++
 src/cnetz/fsk_fm_demod.h |  1 +
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/cnetz/cnetz.c b/src/cnetz/cnetz.c
index 7519241..b177f65 100644
--- a/src/cnetz/cnetz.c
+++ b/src/cnetz/cnetz.c
@@ -75,6 +75,30 @@
  * read also in the C-Netz specs.
  */
 
+/*
+ * Notes on switching from OgK to SpK
+ *
+ * Upon transmission of TRANS_VAG and TRANS_VAK, the SpK channel is allocated,
+ * set to busy, scheduled to switch to SpK mode after two frames. The trans-
+ * action is relinked from OgK to SpK.
+ *
+ * In case of a combined OgK+SpK, the channel stays the same, but will change.
+ *
+ * See below for detailled processing.
+ */
+
+/*
+ * Notes on database (subscriber)
+ *
+ * If a subscriber registers (transaction is created), an instance of the
+ * subscriber database is created. A timer is running for each instance, so
+ * the subscriber is paged to check availability of the phone. If the paging
+ * fails, a retry counter is decreased until the subscriber is removed from
+ * database.
+ *
+ * See database.c for more information.
+ */
+
 /*
  * Notes on the combined channel hack:
  *
@@ -899,7 +923,7 @@ wbn:
 			} else {
 				PDEBUG(DCNETZ, DEBUG_INFO, "Assigning phone to traffic channel %d\n", spk->sender.kanal);
 				/* sync RX time to current OgK time */
-				spk->fsk_demod.bit_time = cnetz->fsk_demod.bit_time;
+				fsk_copy_sync(&spk->fsk_demod, &cnetz->fsk_demod);
 			}
 			/* set channel */
 			telegramm.frequenz_nr = spk->sender.kanal;
diff --git a/src/cnetz/fsk_fm_demod.c b/src/cnetz/fsk_fm_demod.c
index a7247f0..f4008f4 100644
--- a/src/cnetz/fsk_fm_demod.c
+++ b/src/cnetz/fsk_fm_demod.c
@@ -456,6 +456,12 @@ void fsk_correct_sync(fsk_fm_demod_t *fsk, double offset)
 	fsk->bit_time = fmod(fsk->bit_time - offset + BITS_PER_SUPERFRAME, BITS_PER_SUPERFRAME);
 }
 
+/* copy sync from one instance to another (used to sync RX of SpK to OgK */
+void fsk_copy_sync(fsk_fm_demod_t *fsk_to, fsk_fm_demod_t *fsk_from)
+{
+	fsk_to->bit_time = fsk_from->bit_time;
+}
+
 void fsk_demod_reset(fsk_fm_demod_t *fsk)
 {
 	fsk->sync = FSK_SYNC_NONE;
diff --git a/src/cnetz/fsk_fm_demod.h b/src/cnetz/fsk_fm_demod.h
index 0c51e70..b1889bd 100644
--- a/src/cnetz/fsk_fm_demod.h
+++ b/src/cnetz/fsk_fm_demod.h
@@ -53,5 +53,6 @@ typedef struct fsk_fm_demod {
 int fsk_fm_init(fsk_fm_demod_t *fsk, cnetz_t *cnetz, int samplerate, double bitrate);
 void fsk_fm_demod(fsk_fm_demod_t *fsk, int16_t *samples, int length);
 void fsk_correct_sync(fsk_fm_demod_t *fsk, double offset);
+void fsk_copy_sync(fsk_fm_demod_t *fsk_to, fsk_fm_demod_t *fsk_from);
 void fsk_demod_reset(fsk_fm_demod_t *fsk);