From f72c53757d4ce30c37ecefda825f21f42c60b05e Mon Sep 17 00:00:00 2001
From: Andreas Eversberg <jolly@eversberg.eu>
Date: Sun, 29 Jan 2017 07:27:08 +0100
Subject: [PATCH] B-Netz, NMT: Improved check for minimum required sample rate

---
 src/bnetz/dsp.c |  8 ++++++--
 src/nmt/dsp.c   | 10 +++++-----
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/bnetz/dsp.c b/src/bnetz/dsp.c
index 70b4649..3d1e127 100644
--- a/src/bnetz/dsp.c
+++ b/src/bnetz/dsp.c
@@ -83,8 +83,12 @@ int dsp_init_sender(bnetz_t *bnetz)
 	sample_t *spl;
 	int i;
 
-	if ((bnetz->sender.samplerate % 1000)) {
-		PDEBUG(DDSP, DEBUG_ERROR, "Samples rate must be a multiple of 1000 bits per second.\n");
+	if ((bnetz->sender.samplerate % (int)(1.0 / (double)BIT_DURATION))) {
+		PDEBUG(DDSP, DEBUG_ERROR, "Samples rate must be a multiple of %d bits per second.\n", (int)(1.0 / (double)BIT_DURATION));
+		return -EINVAL;
+	}
+	if ((bnetz->sender.samplerate % (int)(1.0 / (double)FILTER_STEP))) {
+		PDEBUG(DDSP, DEBUG_ERROR, "Samples rate must be a multiple of %d bits per second.\n", (int)(1.0 / (double)FILTER_STEP));
 		return -EINVAL;
 	}
 
diff --git a/src/nmt/dsp.c b/src/nmt/dsp.c
index 3d7dd52..65dc8ae 100644
--- a/src/nmt/dsp.c
+++ b/src/nmt/dsp.c
@@ -120,8 +120,8 @@ int dsp_init_sender(nmt_t *nmt)
 	/* attack (3ms) and recovery time (13.5ms) according to NMT specs */
 	init_compandor(&nmt->cstate, 8000, 3.0, 13.5, COMPANDOR_0DB);
 
-	/* this should not happen. it is implied by previous check */
-	if (nmt->supervisory && nmt->sender.samplerate < 12000) {
+	/* a symbol rate of 1200 Hz, times check interval of FILTER_STEPS */
+	if (nmt->sender.samplerate < (double)BIT_RATE / (double)FILTER_STEPS) {
 		PDEBUG(DDSP, DEBUG_ERROR, "Sample rate must be at least 12000 Hz to process FSK+supervisory signal.\n");
 		return -EINVAL;
 	}
@@ -313,7 +313,7 @@ static inline void fsk_decode_step(nmt_t *nmt, int pos)
 	spl = nmt->fsk_filter_spl;
 
 	/* count time in bits */
-	nmt->rx_bits_count += 0.1;
+	nmt->rx_bits_count += FILTER_STEPS;
 
 	level = audio_level(spl, max);
 	/* limit level to prevent division by zero */
@@ -462,8 +462,8 @@ void sender_receive(sender_t *sender, sample_t *samples, int length)
 		}
 		/* if 1/10th of a bit duration is reached, decode buffer */
 		step += bps;
-		if (step >= 0.1) {
-			step -= 0.1;
+		if (step >= FILTER_STEPS) {
+			step -= FILTER_STEPS;
 			fsk_decode_step(nmt, pos);
 		}
 	}