Update ESP32 platform and LoRa batching

src/lora_transport.cpp

@@ -1,6 +1,7 @@
 #include "lora_transport.h"
 #include <LoRa.h>
 #include <SPI.h>
+#include <math.h>
 
 static uint16_t crc16_ccitt(const uint8_t *data, size_t len) {
   uint16_t crc = 0xFFFF;
@@ -106,3 +107,28 @@ bool lora_receive(LoraPacket &pkt, uint32_t timeout_ms) {
 void lora_sleep() {
   LoRa.sleep();
 }
+
+uint32_t lora_airtime_ms(size_t packet_len) {
+  if (packet_len == 0) {
+    return 0;
+  }
+
+  const double bw = static_cast<double>(LORA_BANDWIDTH);
+  const double sf = static_cast<double>(LORA_SPREADING_FACTOR);
+  const double cr = static_cast<double>(LORA_CODING_RATE - 4); // coding rate denominator: 4/(4+cr)
+  const double tsym = (1 << LORA_SPREADING_FACTOR) / bw;
+  const double t_preamble = (static_cast<double>(LORA_PREAMBLE_LEN) + 4.25) * tsym;
+
+  const bool low_data_rate_opt = (LORA_SPREADING_FACTOR >= 11) && (LORA_BANDWIDTH <= 125000);
+  const double de = low_data_rate_opt ? 1.0 : 0.0;
+  const double ih = 0.0;
+  const double crc = 1.0;
+
+  const double payload_symb_nb = 8.0 + max(
+    ceil((8.0 * packet_len - 4.0 * sf + 28.0 + 16.0 * crc - 20.0 * ih) / (4.0 * (sf - 2.0 * de))) * (cr + 4.0),
+    0.0);
+  const double t_payload = payload_symb_nb * tsym;
+  const double t_packet = t_preamble + t_payload;
+
+  return static_cast<uint32_t>(ceil(t_packet * 1000.0));
+}