CCS/CC1350: CRC decryption C/c++/java code implementation for validating if the packet is valid and not corrupted

Im talking on CC1350 launchpad and not cc1311 so please be cautious about that !

Meaning that you are no longer using IQ samples as you were using in this thread:

The previous thread contained a function for calculating the CRC.

Also from the previous threads I got the impression that you are not describing what you are doing in full. Could you describe in more detail why you are implementing the system the way you are doing? That would it make it easier to answer your question.

Hi , I'm receving a packet and decrypting it , this mean I want to check if my recieved packet is valid or not , so I want to know what format type does cc1350 in order to calculate CRC , I want to know by CRC of my recieved packet if it's valid or not valid... so I have CRC of my recieved packet and I know it , my question how can I validate by its crc if my packet valid or not by its?

Please answer the questions from the thread I pointed to. This http://dev.ti.com/tirex/content/simplelink_cc13x0_sdk_4_10_01_01/docs/proprietary-rf/proprietary-rf-users-guide/proprietary-rf/packet-format.html#crc-calculation gives information on the Polynom used and how to calculate this in code.

If this doesn't cover what you want to know, please elaborate and be clear on why you need something else and why what we have suggested doesn't work. 

Hi ;

this isn't enough !

I will explain again, I have packet it's in binary bits, I save it in array called rxbuffer[] , so assume I have this received packet saved in rxbuffer[] ,

rxbuffer=[10000000000010101010101010101010101010101010101001010CRC] , I mean by CRC lets assue it's 0101 .

so now I want to validate this packet if it's valid or not ... how can I do/implement a function to validate this received packet that's saved in rcbuffer as input (rxbuffer is an array that has the received packet and it's as input to my function to validate if this received packet is valid or not valid) 

Again: To be able to use CRC, the CRC is calculated on the TX side and appended to the packet. Meaning that you have [preamble][sync][payload][CRC] sent on the air. On the receive side you calculate the CRC over [payload] and compare with the CRC you receive.

You need to know how the CRC is calculated on the TX side. If CC13xx is on the TX side, you know how this is calculated based on the link in my last post. 

Then you can calculate the CRC on your received rxBuffer with the same function.

If this does not cover what you want to know, elaborate. Please don't just copy/ paste what you have written so far. 

HERE IS EXACTLY MY PROBLEM: how do I calculate the CRC over payload in order to compare it to my received CRC? thanks!

I've read on the internet how to calculate CRC, they are many types, it might be xor with data .. but not sure of that it depends on the type of crc implementation.

Im about two weeks on how to calculate my CRC on the received packet rxbuffer=[10000000000010101010101010101010101010101010101001010CRC] and didn't succeed!

Have you tried the function given in http://dev.ti.com/tirex/content/simplelink_cc13x0_sdk_4_10_01_01/docs/proprietary-rf/proprietary-rf-users-guide/proprietary-rf/packet-format.html#crc-calculation and if yes, what fails? 

the given function is txbuffer, and its values are no't in binary like my case !

in my case I have rxbuffer=[010101010100000000000000000000000011110000000000110] ; which it's has binary values of the received packet ..

and it didn't work for me

The function operate on bytes, I assume you have converted your data into bytes before you pass them to the function?

You write that "it didn't work". Please show how you tried to calculate the CRC.  

#define CRC16_POLY 0x8005
UINT16 culCalcCRC(BYTE crcData, UINT16 crcReg) {
    UINT8 i;
    for (i = 0; i < 8; i++) {
        if (((crcReg & 0x8000) >> 8) ^ (crcData & 0x80)) {
            crcReg = (crcReg << 1) ^ CRC16_POLY;
        } else {
          crcReg = (crcReg << 1);
        }
        crcData <<= 1;
    }
    return crcReg;
}// culCalcCRC


//----------------------------------------------------------------
// Example of Usage

#define CRC_INIT 0xFFFF
UINT8 rxBuffer = {100000000000111111111111101100000000000001110000000111101010101110110000101};
UINT16 checksum;
UINT8 i;

checksum = CRC_INIT; // Init value for CRC calculation

for (i = 0; i < sizeof(rxBuffer); i++) {
  checksum = culCalcCRC(rxBuffer[i], checksum);
}

if it works, then I wouldn't ask :)

It looks like you haven't converted your buffer from binary and into bytes before passing it to the function? 

into bytes? you mean into integers? it would be appreciated to elaborate what do you mean into bytes

you mean every byte in my stream bits to convert it to integer?

Any help guys?! thanks

Have you looked into something like this: 

https://stackoverflow.com/questions/13667746/converting-from-8-bits-to-1-byte

Yes , its peoblem for string 8bits .. but my problem is that my string(rxbuffer) is more than 8bits!

If you have a buffer with n bits you have to convert this to buffer that contains n/8 bytes. So every 8 bits you have in your buffer you convert into one byte. 

So In order to understand 100% , I will have another array that have every 8bit  seperately like this : convertedbuffer={11111101,00001010,01010101,00000001,11111111}

And then I convert those data(every 8bit data) to integer?

I mean what should my converted rxbuffer array be like in order to input it to the function that we talked about?

I succeeded to convert my binary data rxbuffer[] to Byte data I mean to type unit8_t 

now I have rxbuffer like this unit8 rxbuffer={5, 1, 2, 3, 4, 5, 0, 0};

so how now I compare between my received CRC to my transmitted CRC?

thanks for any explanation.

Hi, any assistance please?

Have you calculated a CRC based on this sequence and compared to the CRC you receive? 

here's my problem, how do I calculate the CRC? the CRC that I recieve is ok I know it, but the CRC of my transmitted packet how I calculate it?

in order to compare between them I want to know the CRC based on this sequence .. 

Any help guys?

I've the CRC in my received packet, and I know it .. now how do I compare it with my other CRC I dont know the other CRC any help?! thanks alot

@TER

Appreciate your answer but still it's not clearly much!

lets assume I send by smartRFstudio a packet with payload (including length) FFFFFFFFFFFFFFFF , and once I received it I see the CRC of the received packet. so now what should I do in order to calculate the correct CRC? or how to know my correct CRC in order to be able to compare it to the my received packet CRC? .. it would be appreciated if you take my example and explain in an interpreted explanation. 

thanks alot