CRC Library Problem with CRC16

Projects Programming
1

I am trying to understand how the CRC library in Arduino IDE works but I think I have encountered a possible error or possibly it is on my end so I am asking this to figure out which is which.
This is the slightly modified example code called CRC_test.ino from the library itself:

//
//    FILE: CRC_test.ino
//  AUTHOR: Rob Tillaart
// PURPOSE: demo
//     URL: https://github.com/RobTillaart/CRC


#include "CRC.h"
#include "printHelpers.h"  //  for the 64 bit...

char str[24] = "123456789";


void setup() {
  Serial.begin(115200);
  //Serial.println(__FILE__);

  //Serial.println("Verified with - https://crccalc.com/ \n");

}

void loop() {
  uint8_t *data = (uint8_t *)&str[0];
  //  use default parameters for calcCRCxx()
  Serial.print("TEST:\t");
  Serial.println(str);
  Serial.print("CRC8:\t");
  Serial.println(calcCRC8(data, 9), HEX);
  Serial.print("CRC16:\t");
  Serial.println(calcCRC16(data, 9), HEX);
  Serial.print("CRC32:\t");
  Serial.println(calcCRC32(data, 9), HEX);
  //  Serial.print("*CRC64:\t");
  //  uint64_t t = calcCRC64(data, 9);
  //  Serial.println(print64(t, HEX));

  Serial.println("\n\nDone...");
  delay(5000);
}


//  -- END OF FILE --

Serial monitor output is this:

17:01:52.121 -> TEST: 123456789

17:01:52.121 -> CRC8: F4

17:01:52.121 -> CRC16: A829

17:01:52.121 -> CRC32: CBF43926

17:01:52.121 ->

17:01:52.121 ->

17:01:52.121 -> Done...

I don't know if the forum will let me post a picture since i am still a new user but using the link provided in the code I checked for CRC8, CRC16 and CRC32 and as I can see CRC8 checks out with CRC-8/SMBUS and CRC32 checks out with CRC-32/ISO-HDLC but I haven't able to verify CRC16 result printed on the serial monitor with any of the CRC results provided in the calculator.

I have checked with a few other calculators and they seem to be verifying each other so I don't know what went wrong with the code so if anyone can tell me what am I doing wrong, that will be greatly appreciated.

2

Have you looked at the code for CRC16 in the Arduino library to see if uses the same polynomial as the online calculators you checked?

EDIT:
See CrcParameters.h:

//  CRC 16
#define CRC16_POLYNOME              0x8001 // x15 + 1 =  1000 0000 0000 0001 = 0x8001

There are other CRC16 options in that library that do have matching polynomials to your those in your online calculator. Try one of those.

3

No, I haven't yet delved into the source code since this was the calculator the author provided in the code itself to verify the results, i assumed it would have the correct output format to match the one used in the code.

4

Bad assumption. There are multiple, equally valid polynomials that can be used for CRC16. The library supports this. If you want a comparison between two CRC calculations to match, you must use the same polynomial for each.

1 Like
5

thanks for help, Thank you so much for guiding, we want to configure it in our touch screens pos

6

In CRC algorithms, the polynomial isn't the only option. There are also starting and ending XOR values.

The reveng program library has lots of useful background info, and is a great tool for figuring out what options were used in a given CRC calculation.

7

Yup. But given that CRC8 and CRC32 "worked" for @thunguskha, I'd be willing to bet that the library's default parameters for those are the same as what the cited online calculator uses. So, first thing I'd try is:

 Serial.println(calcCRC16(data, 9, CRC16_CCITT_POLYNOME), HEX);
8

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