From 629ac5585aedb0993acfee66e7ba58dac312eb27 Mon Sep 17 00:00:00 2001
From: jgromes <jgromes@users.noreply.github.com>
Date: Fri, 26 Jul 2019 09:43:24 +0200
Subject: [PATCH] [SX126x] Added method to get expected time-on-air

---
 keywords.txt           |  1 +
 src/modules/SX126x.cpp | 39 +++++++++++++++++++++++----------------
 src/modules/SX126x.h   |  9 +++++++++
 3 files changed, 33 insertions(+), 16 deletions(-)

diff --git a/keywords.txt b/keywords.txt
index 7a47ab48..1e47e76e 100644
--- a/keywords.txt
+++ b/keywords.txt
@@ -105,6 +105,7 @@ setGdo1Action	KEYWORD2
 setDio2Action	KEYWORD2
 setTCXO	KEYWORD2
 setDio2AsRfSwitch	KEYWORD2
+getTimeOnAir	KEYWORD2
 
 # ESP8266
 join	KEYWORD2
diff --git a/src/modules/SX126x.cpp b/src/modules/SX126x.cpp
index 93327118..94b9c581 100644
--- a/src/modules/SX126x.cpp
+++ b/src/modules/SX126x.cpp
@@ -157,25 +157,11 @@ int16_t SX126x::transmit(uint8_t* data, size_t len, uint8_t addr) {
   uint8_t modem = getPacketType();
   if(modem == SX126X_PACKET_TYPE_LORA) {
     // calculate timeout (150% of expected time-on-air)
-    float symbolLength = (float)((uint32_t)(1) << _sf) / (float)_bwKhz;
-    float sfCoeff1 = 4.25;
-    float sfCoeff2 = 8.0;
-    if(_sf == 5 || _sf == 6) {
-      sfCoeff1 = 6.25;
-      sfCoeff2 = 0.0;
-    }
-    uint8_t sfDivisor = 4*_sf;
-    if(symbolLength >= 16.0) {
-      sfDivisor = 4*(_sf - 2);
-    }
-    float nSymbol = _preambleLength + sfCoeff1 + 8 + ceil(max(8.0 * len + (_crcType * 16.0) - 4.0 * _sf + sfCoeff2 + 20.0, 0.0) / sfDivisor) * (_cr + 4);
-    timeout = (uint32_t)(symbolLength * nSymbol * 1500.0);
+    timeout = (float)getTimeOnAir(len) * 1.5;
 
   } else if(modem == SX126X_PACKET_TYPE_GFSK) {
-
     // calculate timeout (500% of expected time-on-air)
-    float brBps = ((float)(SX126X_CRYSTAL_FREQ) * 1000000.0 * 32.0) / (float)_br;
-    timeout = (uint32_t)(((len * 8.0) / brBps) * 1000000.0 * 5.0);
+    timeout = (float)getTimeOnAir(len) * 5.0;
 
   } else {
     return(ERR_UNKNOWN);
@@ -877,6 +863,27 @@ size_t SX126x::getPacketLength(bool update) {
   return((size_t)rxBufStatus[0]);
 }
 
+uint32_t SX126x::getTimeOnAir(size_t len) {
+  if(getPacketType() == SX126X_PACKET_TYPE_LORA) {
+    float symbolLength = (float)((uint32_t)(1) << _sf) / (float)_bwKhz;
+    float sfCoeff1 = 4.25;
+    float sfCoeff2 = 8.0;
+    if(_sf == 5 || _sf == 6) {
+      sfCoeff1 = 6.25;
+      sfCoeff2 = 0.0;
+    }
+    uint8_t sfDivisor = 4*_sf;
+    if(symbolLength >= 16.0) {
+      sfDivisor = 4*(_sf - 2);
+    }
+    float nSymbol = _preambleLength + sfCoeff1 + 8 + ceil(max(8.0 * len + (_crcType * 16.0) - 4.0 * _sf + sfCoeff2 + 20.0, 0.0) / sfDivisor) * (_cr + 4);
+    return((uint32_t)(symbolLength * nSymbol * 1000.0));
+  } else {
+    float brBps = ((float)(SX126X_CRYSTAL_FREQ) * 1000000.0 * 32.0) / (float)_br;
+    return((uint32_t)(((len * 8.0) / brBps) * 1000000.0));
+  }
+}
+
 int16_t SX126x::setTCXO(float voltage, uint32_t timeout) {
   // set mode to standby
   standby();
diff --git a/src/modules/SX126x.h b/src/modules/SX126x.h
index 9f9253b4..134325bd 100644
--- a/src/modules/SX126x.h
+++ b/src/modules/SX126x.h
@@ -690,6 +690,15 @@ class SX126x: public PhysicalLayer {
     */
     size_t getPacketLength(bool update = true);
 
+    /*!
+     \brief Get expected time-on-air for a given size of payload
+
+     \param len Payload length in bytes.
+
+     \returns Expected time-on-air in microseconds.
+   */
+   uint32_t getTimeOnAir(size_t len);
+
   protected:
     // SX1276x SPI command implementations
     int16_t setTx(uint32_t timeout = 0);