From 01c629a6fdcbec481a9fc15a39341ffc60a7c135 Mon Sep 17 00:00:00 2001
From: Mark Qvist <mark@adepta.io>
Date: Tue, 24 Apr 2018 15:34:50 +0200
Subject: [PATCH] Improved data carrier detection

---
 device.h        |  2 +-
 hardware/AFSK.c | 21 +++++++++++++++++++--
 hardware/AFSK.h |  4 ++++
 protocol/KISS.c |  2 +-
 4 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/device.h b/device.h
index c26447a..499ae09 100755
--- a/device.h
+++ b/device.h
@@ -9,7 +9,7 @@
 #define FREQUENCY_CORRECTION 0
 
 // ADC settings
-#define OPEN_SQUELCH false
+#define OPEN_SQUELCH true
 #define ADC_REFERENCE REF_3V3
 // OR
 //#define ADC_REFERENCE REF_5V
diff --git a/hardware/AFSK.c b/hardware/AFSK.c
index 7c234c2..f82a81f 100755
--- a/hardware/AFSK.c
+++ b/hardware/AFSK.c
@@ -205,6 +205,14 @@ static bool hdlcParse(Hdlc *hdlc, bool bit, FIFOBuffer *fifo) {
             // on the RX LED.
             fifo_push(fifo, HDLC_FLAG);
             hdlc->receiving = true;
+
+            if (hdlc->dcd_count < DCD_MIN_COUNT) {
+                hdlc->dcd = false;
+                hdlc->dcd_count++;
+            } else {
+                hdlc->dcd = true;
+            }
+
             #if OPEN_SQUELCH == false
                 LED_RX_ON();
             #endif
@@ -215,7 +223,8 @@ static bool hdlcParse(Hdlc *hdlc, bool bit, FIFOBuffer *fifo) {
             
             ret = false;
             hdlc->receiving = false;
-            LED_RX_OFF();
+            hdlc->dcd = false;
+            hdlc->dcd_count = 0;
         }
 
         // Everytime we receive a HDLC_FLAG, we reset the
@@ -239,10 +248,18 @@ static bool hdlcParse(Hdlc *hdlc, bool bit, FIFOBuffer *fifo) {
         // If we have, something probably went wrong at the
         // transmitting end, and we abort the reception.
         hdlc->receiving = false;
-        LED_RX_OFF();
+        hdlc->dcd = false;
+        hdlc->dcd_count = 0;
         return ret;
     }
 
+    // Check the DCD status and set RX LED appropriately
+    if (hdlc->dcd) {
+        LED_RX_ON();
+    } else {
+        LED_RX_OFF();
+    }
+
     // If we have not yet seen a HDLC_FLAG indicating that
     // a transmission is actually taking place, don't bother
     // with anything.
diff --git a/hardware/AFSK.h b/hardware/AFSK.h
index e171fd8..8a0169f 100755
--- a/hardware/AFSK.h
+++ b/hardware/AFSK.h
@@ -51,6 +51,8 @@ inline static uint8_t sinSample(uint16_t i) {
 
 #define SAMPLESPERBIT (SAMPLERATE / BITRATE)
 #define PHASE_INC    1                              // Nudge by an eigth of a sample each adjustment
+
+#define DCD_MIN_COUNT 6
                        
 #if BITRATE == 960
     #define FILTER_CUTOFF 600
@@ -80,6 +82,8 @@ typedef struct Hdlc
     uint8_t bitIndex;
     uint8_t currentByte;
     bool receiving;
+    bool dcd;
+    uint8_t dcd_count;
 } Hdlc;
 
 typedef struct Afsk
diff --git a/protocol/KISS.c b/protocol/KISS.c
index 0c6e967..ad175c5 100755
--- a/protocol/KISS.c
+++ b/protocol/KISS.c
@@ -49,7 +49,7 @@ void kiss_csma(AX25Ctx *ctx, uint8_t *buf, size_t len) {
     bool sent = false;
     while (!sent) {
         //puts("Waiting in CSMA");
-        if(!channel->hdlc.receiving) {
+        if(!channel->hdlc.dcd) {
             uint8_t tp = rand() & 0xFF;
             if (tp < p) {
                 ax25_sendRaw(ctx, buf, len);