AVR Freaks

thanks WinterBottom. i'm passing arrays from main.c to the function along with it sizes.  

It should not exceed 11 bytes but i allocate 255 bytes for the payload. Is this overallocation giving a problem?

uint8_t NAKMessage[] = {0x4E, 0x41, 0x4B};
uint8_t ACKMessage[] = {0x41, 0x43, 0x4B};

void LoRa_Send(uint8_t payload[], uint8_t payload_length)
{
    uint8_t data[255];
    uint8_t length = payload_length + 8;
    
    data[0]        = 0x27;            //LORA protocol marker
    data[1]        = ID[0];
    data[2]        = ID[1];
    data[3]        = ID[2];
    data[4]        = ID[3];
    data[5]        = 0;            //count
    data[6]        = payload_length;
    data[7]        = 0;            //checksum: 0xEC
    
    for(uint8_t j=0; j <payload_length; j++)
    {
        data[j+8] = payload[j];
    }
        
    uint8_t checkSum = LoRa_calcCheckSum(data,length);
    data[7] = checkSum;

    //beginPacket
    //explicitHeaderMode
    RFM95_readReg(REG_MODEM_CONFIG_1);
    RFM95_writeReg(REG_MODEM_CONFIG_1,  0x72);
    // reset FIFO address and payload length
    RFM95_writeReg(REG_FIFO_ADDR_PTR, 0);
    RFM95_writeReg(REG_PAYLOAD_LENGTH, 0);
    
    // write data
    uint8_t currentLength = RFM95_readReg(REG_PAYLOAD_LENGTH);
    
    // check size
    if ((currentLength + length) > MAX_PKT_LENGTH) {
        length = MAX_PKT_LENGTH - currentLength;
    }
    for (uint8_t i = 0; i < length; i++) {
        RFM95_writeReg(REG_FIFO, data[i]);
    }
    
    // update length
    RFM95_writeReg(REG_PAYLOAD_LENGTH, currentLength + length);
         
    // put in TX mode
    RFM95_writeReg(REG_OP_MODE, MODE_LONG_RANGE_MODE | MODE_TX);
    
    while ((RFM95_readReg(REG_IRQ_FLAGS) & IRQ_TX_DONE_MASK) == 0) {
        _delay_ms(1);
    }
    // clear IRQ's
    RFM95_writeReg(REG_IRQ_FLAGS, IRQ_TX_DONE_MASK);
}
 

brilliant, curtvm. Once i revise the allocation to 100 instead of 255 it works as expected. Thanks everyone