A Cyclic Redundancy Check (CRC) is a verification method used to ensure that data being sent is not corrupted during transfer. The use of CRCs is common in communication mediums that transmit digital data, such as WiFi and Ethernet. There is a need to check for communication errors in embedded systems, as technology drives them to be capable of creating and sending larger data packets in a faster and more complex manner.

The CRC algorithm computes a checksum for each specific data set that is sent through it. This algorithm utilizes a polynomial key and the transferred data.

The sending system calculates the check or verification code and appends it to the outgoing message. On the receiving end, the data is put through the same process. If the CRC produced at the receiving end does not match the sent CRC, then the data is possibly corrupt. The receiver can request that the data be retransmitted or simply ignore the data. When the CRC matches the received version, the user can be fairly confident that the transmission is not corrupted.

Implementing CRCs is accomplished using two different methods. The brute force method requires more computational resources and can be more time consuming. The lookup table method requires more memory resources and is useful for defined and/or repetitive data sets.

The calculator qCRC provided here, uses the brute force method. CRC math can be accomplished in software by shifting the data or shifting the polynomial key, then performing the computations. Supported CRCs include 8, 16 and 32-bit in a generic way, this means that you can specify the polynomial key, the CRC initial value, I/O reflection and XOR the final output value. This generic approach allows the user to implement any variant of CRC(8,16,32) only by adjusting these parameters.

Example: A code snippet to compute the CRC-16/KERMIT.

Validate against http://www.sunshine2k.de/coding/javascript/crc/crc_js.html

char data[] = "123456789";
uint32_t crc_value;
 
crc_value = qCRCx( QCRC16, data, strlen(data), 0x1021, 0x0000, 1u, 1u, 0x0000 );