From cb4352a996d82d2b786ca3405029b31bba49a758 Mon Sep 17 00:00:00 2001
From: John Greb <hexameron@spam.no>
Date: Sat, 17 Jan 2015 15:59:44 +0000
Subject: [PATCH] Bit tools.

---
 plugins/channel/lora/lorabits.h    | 36 ++++++++++++++++++++++++++++++
 plugins/channel/lora/lorademod.cpp | 20 ++++++++++-------
 plugins/channel/lora/lorademod.h   |  9 ++++----
 3 files changed, 53 insertions(+), 12 deletions(-)
 create mode 100644 plugins/channel/lora/lorabits.h

diff --git a/plugins/channel/lora/lorabits.h b/plugins/channel/lora/lorabits.h
new file mode 100644
index 000000000..0f238d897
--- /dev/null
+++ b/plugins/channel/lora/lorabits.h
@@ -0,0 +1,36 @@
+/*
+ Interleaving is "easiest" if the same number of bits is used per symbol as for FEC
+ Chosen mode "spreading 8, low rate" has 6 bits per symbol, so use 4:6 FEC
+*/
+
+// Needs adjusting for different sizes
+void interleave(short* inout)
+{
+	int i, index = 6;
+	short in[index * 2];
+	for (i = 0; i < index; i++)
+		in[i] = inout[i];
+	for (i = 0; i < index; i++) {
+		inout[i] = (1 & in[0 + i]) | (2 & in[1 + i]) | (4 & in[2 + i])
+			| (8 & in[3 + i]) | (16 & in[4 + i]) | (32 & in[5 + i]); 
+		in[i + index] = in[i];
+	}
+}
+
+// Same sequence for any size
+void make_gray(void)
+{
+	short gray[1<<8];
+//	short ungray[1<<8];
+	short k = 0;
+	for (short i = 0; i < 1<<8; i++) {
+		gray[i] = k;
+//		ungray[k] = i;
+		short r = (i+1) & ~i;
+		k ^= r;
+	}
+//	for (short i = 0; i < 1<<5; i++)
+//		printf("%x:%x:%x.\n", i, gray[i], ungray[gray[i]]);
+}
+
+
diff --git a/plugins/channel/lora/lorademod.cpp b/plugins/channel/lora/lorademod.cpp
index f10dca46e..ea70f0720 100644
--- a/plugins/channel/lora/lorademod.cpp
+++ b/plugins/channel/lora/lorademod.cpp
@@ -40,6 +40,7 @@ LoRaDemod::LoRaDemod(SampleSink* sampleSink) :
 	m_bin = 0;
 	m_result = 0;
 	m_count = 0;
+	m_header = 0;
 
 	loraFilter = new sfft(LORA_SFFT_LEN);
 	negaFilter = new sfft(LORA_SFFT_LEN);
@@ -64,8 +65,8 @@ void LoRaDemod::configure(MessageQueue* messageQueue, Real Bandwidth)
 
 int  LoRaDemod::detect(Complex c, Complex a)
 {
-	int i;
-	float peak;
+	int i, result, negresult;
+	float peak, negpeak;
 	float mag[LORA_SFFT_LEN];
 	float rev[LORA_SFFT_LEN];
 
@@ -77,18 +78,21 @@ int  LoRaDemod::detect(Complex c, Complex a)
 	// process spectrum every 32 samples
 	loraFilter->fetch(mag);
 	negaFilter->fetch(rev);
-	peak = 0.0f;
-	m_result = 0;
+	peak = negpeak = 0.0f;
+	result = negresult = 0;
 	for (i = 0; i < LORA_SFFT_LEN; i++) {
-		if (rev[i]/3 > peak) {
-			peak = rev[i]/3;
-			m_result = i;
+		if (rev[i] > negpeak) {
+			negpeak = rev[i];
+			negresult = i;
 		}
 		if (mag[i] > peak) {
 			peak = mag[i];
-			m_result = i;
+			result = i;
 		}
 	}
+	if (peak > negpeak) {
+		m_result = result;
+	}
 	return m_result;
 }
 
diff --git a/plugins/channel/lora/lorademod.h b/plugins/channel/lora/lorademod.h
index 33da4ada3..db2c029c3 100644
--- a/plugins/channel/lora/lorademod.h
+++ b/plugins/channel/lora/lorademod.h
@@ -25,10 +25,10 @@
 #include "util/message.h"
 #include "dsp/fftfilt.h"
 
-#define SPREADFACTOR (1<<8)
-
-/* Chosen for number of bins, not symbol length */
-#define LORA_SFFT_LEN (128)
+#define DATA_BITS (6)
+#define SAMPLEBITS (DATA_BITS + 2)
+#define SPREADFACTOR (1 << SAMPLEBITS)
+#define LORA_SFFT_LEN (SPREADFACTOR / 2)
 
 class LoRaDemod : public SampleSink {
 public:
@@ -73,6 +73,7 @@ private:
 	int m_bin;
 	int m_result;
 	int m_count;
+	int m_header;
 
 	sfft* loraFilter;
 	sfft* negaFilter;