CODEWITHSUNDEEP
arduinoarduino-due
Chris
Chris

Reputation: 1128

Byte truncation casting from void* on Arduino

I'm hoping that someone can help me diagnose this odd behavior that I'm experiencing. I'm programming for the Arduino Due and using the Adafruit FONA modem. The code in question submits an array of bytes to be sent over the modem. sendData is taking an unsigned char[] which I cast to void*. data_len is the number of bytes written to the buffer rather than the size of the buffer itself.

The board I'm working with doesn't use printf/sprintf to print to stdout. Instead this is done using Serial.print and Serial.println. Serial here is an Arduino class, not the standard C++ class. sprintf_ByteArray I wrote to examine the contents of a byte buffer, with the results reflected as hex bytes.

As I mentioned my ultimate goal here is to write data to the modem. This is done in the fonaSerial->println and fonaSerial->write calls. The first issues a modem command with the size of the data to be written. The second writes the data.

But I'm experiencing something screwy. The result of printing data and String message is displayed below. Inexplicably to me, message only contains the last 119 bytes of data. At first, this didn't surprise me as data includes null bytes and I assumed that those were somehow to blame. But, message actually includes null bytes! And, I would have expected message to represent the first N bytes of data, up until the first null byte.

Lastly: I end by casting data to a uint8_t* and passing to fonaSerial->write. Initially I had been passing a String but after I had trouble casting I decided to try this alternative tack. I then send this data to a server I'm running. The server only gets a payload of 119 bytes too.

For the record, earlier I successfully sent a smaller payload. I have no idea what I'm doing now that is causing the problem.

bool sendData(void *data, size_t data_len) {    
  char tmp[1024] = {0};
  Serial.print("data_len=");Serial.println(data_len);
  sprintf_ByteArray(tmp, (unsigned char*) data, data_len);
  Serial.print("Payload (void*)=");Serial.println(tmp);
  String message = (const char*) data;
  Serial.print("Payload (String)=");Serial.println(message);

  fonaSerial->print(F("AT+CIPSEND="));
  fonaSerial->println(data_len);

  fona.readline(3000);
  fonaSerial->write((uint8_t*) data, data_len);
  fonaSerial->flush();

  fona.readline(3000); // wait up to 3 seconds to send the data
  Serial.print (F("\t<--- ")); Serial.println(fona.replybuffer);

  return (strcmp(fona.replybuffer, "SEND OK") == 0);
}

Payload (void*)= 8a a5 62 69 64 00 69 63 6f 6e 64 69 74 69 6f 6e 01 67 62 61 74 74 65 72 79 18 1d 65 73 74 61 74 65 02 69 74 69 6d 65 73 74 61 6d 70 19 0f 95 a5 62 69 64 01 69 63 6f 6e 64 69 74 69 6f 6e 01 67 62 61 74 74 65 72 79 18 42 65 73 74 61 74 65 62 69 74 69 6d 65 73 74 61 6d 70 19 0f 97 a5 62 69 64 02 69 63 6f 6e 64 69 74 69 6f 6e 00 67 62 61 74 74 65 72 79 18 29 65 73 74 61 74 65 06 69 74 69 6d 65 73 74 61 6d 70 19 0f 98 a5 62 69 64 03 69 63 6f 6e 64 69 74 69 6f 6e 01 67 62 61 74 74 65 72 79 18 26 65 73 74 61 74 65 01 69 74 69 6d 65 73 74 61 6d 70 19 0f 99 a5 62 69 64 04 69 63 6f 6e 64 69 74 69 6f 6e 01 67 62 61 74 74 65 72 79 18 2f 65 73 74 61 74 65 62 69 74 69 6d 65 73 74 61 6d 70 19 0f 9a a5 62 69 64 05 69 63 6f 6e 64 69 74 69 6f 6e 01 67 62 61 74 74 65 72 79 18 1d 65 73 74 61 74 65 06 69 74 69 6d 65 73 74 61 6d 70 19 0f 9c a5 62 69 64 18 42 69 63 6f 6e 64 69 74 69 6f 6e 18 75 67 62 61 74 74 65 72 79 18 69 65 73 74 61 74 65 18 6c 69 74 69 6d 65 73 74 61 6d 70 1a 67 6e 69 64 a5 62 69 64 18 20 69 63 6f 6e 64 69 74 69 6f 6e 18 6c 67 62 61 74 74 65 [72 79 18 6f 65 73 74 61 74 65 18 74 69 74 69 6d 65 73 74 61 6d 70 1a 00 6e 39 20 a5 62 69 64 62 69 63 6f 6e 64 69 74 69 6f 6e 00 67 62 61 74 74 65 72 79 18 40 65 73 74 61 74 65 74 69 74 69 6d 65 73 74 61 6d 70 19 0f a0 a5 62 69 64 74 69 63 6f 6e 64 69 74 69 6f 6e 00 67 62 61 74 74 65 72 79 18 43 65 73 74 61 74 65 74 69 74 69 6d 65 73 74 61 6d 70 19 0f a1]

length 471

Payload (String)= 72 79 18 6f 65 73 74 61 74 65 18 74 69 74 69 6d 65 73 74 61 6d 70 1a 00 6e 39 20 a5 62 69 64 62 69 63 6f 6e 64 69 74 69 6f 6e 00 67 62 61 74 74 65 72 79 18 40 65 73 74 61 74 65 74 69 74 69 6d 65 73 74 61 6d 70 19 0f a0 a5 62 69 64 74 69 63 6f 6e 64 69 74 69 6f 6e 00 67 62 61 74 74 65 72 79 18 43 65 73 74 61 74 65 74 69 74 69 6d 65 73 74 61 6d 70 19 0f a1

length 119

Upvotes: 4

Views: 216

Answers (1)

simonecocco
simonecocco

Reputation: 100

try this 'to_string' converter:

String to_string(unsigned char *data,unsigned int len){
    String memtmp="";
    unsigned char tmpdata;
    for(unsigned int i=0;i<len;i++){
        tmpdata=*(data+i);
        memtmp+=String(tmpdata,HEX);
        memtmp+=" ";
    }
    return memtmp;
}

I hope this can help. Good luck!

Upvotes: 0

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