lora_aprs_node_pico/src/main.cpp

#include <stdio.h>
#include <string.h>
#include "pico/stdlib.h"
#include "pico/binary_info.h"
#include "LoRa-RP2040.h"
#include "Config.h"
#include "KISS.h"

bool startRadio();
void getPacketData(int packetLength);

void encode_kiss ();
    
int main() {
  
   /* Among others, this initializes the USB-serial port at 115200bps 8N1 */
   stdio_init_all();
    
   // Buffers
   memset(rxBuffer, 0, sizeof(rxBuffer));
   memset(txBuffer, 0, sizeof(txBuffer));
    
   sleep_ms(5000);

   startRadio();
    
   while (1) {
      int packetSize = LoRa.parsePacket();
      if (packetSize) {
         // received a packet
         printf("Received packet (RSSI = %idBm)\n",LoRa.packetRssi());

         getPacketData(packetSize);
         
         // Check APRS header: must be 0x3C 0xFF 0x01
         if (rxBuffer[0] == 0x3C && rxBuffer[1] == 0xFF && rxBuffer[2] == 0x01 ) {
             // Shift array three places to left (= remove APRS header)
             for (int cnt = 3; cnt < packetSize; cnt++) {
                 rxBuffer[cnt-3] = rxBuffer[cnt];
             }
             rxBuffer[packetSize-3] = 0;
             printf("%s\n", rxBuffer);
             encode_kiss();
         } else {
             printf("ERROR: No or corrupted APRS frame.\n");
         }
      }
  }    
  
  return 0;
}

/*
 * Initializes the LoRa module with the parameters set in config.h
 */
bool startRadio()
{
  // override the default CS, reset, and IRQ pins (optional)
  // LoRa.setPins(7, 6, 1); // set CS, reset, IRQ pin
    
  printf("LoRa settings:\n");
  printf("loraFrequency       = %u\n", loraFrequency);    
  printf("loraSpreadingFactor = %i\n", loraSpreadingFactor);    
  printf("loraPreamble        = %i\n", loraPreamble);    
  printf("loraCodingRate      = %i\n", loraCodingRate);    
  printf("loraTxPower         = %i\n", loraTxPower);    
  printf("LoRaPaSelect        = %i\n", LoRaPaSelect);    
  printf("loraBandwidth       = %u\n", loraBandwidth);    
   
  printf("Starting LoRa radio");
  if (!LoRa.begin(loraFrequency)) {
    printf("  [ FAILED ]\n");
    while(1);
  }
  else {
    LoRa.setPreambleLength(loraPreamble);
    LoRa.setSignalBandwidth(loraBandwidth);
    LoRa.setTxPower(loraTxPower,LoRaPaSelect);
    LoRa.setSpreadingFactor(loraSpreadingFactor);
    LoRa.setCodingRate4(loraCodingRate);
    LoRa.enableCrc();
    printf("  [ DONE ]\n");
  }
}

void getPacketData(int packetLength)
{
  int position = 0;
  
  while (packetLength--) {
    rxBuffer[position++] = LoRa.read();
  }
  rxBuffer[position] = 0;
}

/* Encode LoRa APRS frame: extract source call, digipeater path and data field. At the same time, check for data corruption
 * 
 */
void encode_kiss ()
{
    int position = 0;
    int cnt = 0;
    int number_of_digipeaters = 0;
    char valid_apsr_data = false;
    
    uint8_t aprs_source_address[10];
    uint8_t aprs_digi_path[255];
    uint8_t aprs_data_field[255];  
    uint8_t aprs_digis[10][10];
    
    memset(aprs_source_address, 0, sizeof(aprs_source_address));
    memset(aprs_digi_path, 0, sizeof(aprs_digi_path));
    memset(aprs_data_field, 0, sizeof(aprs_data_field));
    memset(aprs_digis, 0, sizeof(aprs_digis));
   
    // Extract from address
    cnt = 0;    
    while( rxBuffer[position] != 0 )
    {
        aprs_source_address[cnt++] = rxBuffer[position];
        if ( rxBuffer[position] == '>' && position < 10 ) {
            aprs_source_address[cnt-1] = 0;
            valid_apsr_data = true;
            break;
        }
        position++;
    }
    
    position++;
    
    if (valid_apsr_data == true)
    {
        // Extract digi path
        valid_apsr_data = false;
        cnt = 0;
        while( rxBuffer[position] != 0 )
        {
            aprs_digi_path[cnt++] = rxBuffer[position];
            if ( rxBuffer[position] == ':' ) {
                aprs_digi_path[cnt-1] = 0;
                valid_apsr_data = true;
                break;
            }
            position++;
        }
        
    }

    position++;
    
    if (valid_apsr_data == true)
    {
        // Extract data field
        cnt = 0;
        while( rxBuffer[position] != 0 )
        {
            aprs_data_field[cnt++] = rxBuffer[position];
            position++;
        }
        aprs_data_field[cnt] = 0;        
    }    
    
    if (valid_apsr_data == true)
    {
        // Extract digis from digi-path
        cnt = 0;
        position = 0;
        number_of_digipeaters = 0;
        while( aprs_digi_path[position] != 0 )
        {
            aprs_digis[number_of_digipeaters][cnt++] = aprs_digi_path[position];
            if ( aprs_digi_path[position] == ',' && cnt < 10 ) {
                aprs_digis[number_of_digipeaters][cnt-1] = 0;
                if (++number_of_digipeaters > 9) {
                    valid_apsr_data = false;
                    break;
                }
                
                //position++;
                cnt = 0;
            }
            position++;
        }
        aprs_digis[number_of_digipeaters][cnt] = 0;    
    }
    
    if (valid_apsr_data)
        printf("Source address: %s\nDigipeaters (%u): %s %s %s %s\nData: %s\n", aprs_source_address, number_of_digipeaters+1, aprs_digis[0], aprs_digis[1], aprs_digis[2], aprs_digis[3], aprs_data_field);
    else
        printf("Error decoding APRS frame.");
}