CRC (Cyclic Redundancy Check)

General Description

High level interface for interacting with the CRC, which provides hardware accelerated CRC computations.

The CRC APIs are structured to enable usage in situations where the entire input data set is not available in memory at the same time. Therefore, each conversion consists of three steps:

• A single call to cyhal_crc_start, to initialize data structures used to compute CRC
• One or more calls to cyhal_crc_compute, to provide chunks of data
• A single call to cyhal_crc_finish, to finalize the computation and retrieve the result

The table below provides CRC parameters for some common CRC algorithms.

Note

The Expected CRC column shows the computed CRC when the value "123456789" is passed to cyhal_crc_compute.

CRC algorithm Name	Len	Polynomial	Initial seed	Data REV	Data XOR	Rem REV	Remainder XOR	Expected CRC
CRC-6 / CDMA2000-A	6	0x27	0x3F	false	0	false	0x00	0x0D
CRC-6 / CDMA2000-B	6	0x07	0x3F	false	0	false	0x00	0x3B
CRC-6 / DARC	6	0x19	0x00	true	0	true	0x00	0x26
CRC-6 / ITU	6	0x03	0x00	true	0	true	0x00	0x06
CRC-8 / ITU	8	0x07	0x00	false	0	false	0x55	0xA1
CRC-8 / MAXIM	8	0x31	0x00	true	0	true	0x00	0xA1
CRC-8 / ROHC	8	0x07	0xFF	true	0	true	0x00	0xD0
CRC-8 / WCDMA	8	0x9B	0x00	true	0	true	0x00	0x25
CRC-16 / CCITT-0	16	0x1021	0xFFFF	false	0	false	0x0000	0x29B1
CRC-16 / CDMA2000	16	0xC867	0xFFFF	false	0	false	0x0000	0x4C06
CRC-32	32	0x04C11DB7	0xFFFFFFFF	true	0	true	0xFFFFFFFF	0xCBF43926
CRC-32 / BZIP2	32	0x04C11DB7	0xFFFFFFFF	false	0	false	0xFFFFFFFF	0xFC891918

Note

Algorithms that have less than 8 bits, like CRC-6, populate the lower bits and leave the high order bits 0.

Many of the algorithm parameters can be customized.

See crc_algorithm_t and Snippet1: CRC Generation for more details.

Quick Start

cyhal_crc_init initializes the CRC generator and passes the pointer to the CRC block through the obj object of type cyhal_crc_t.

Snippet1: CRC Generation

The following snippet initializes a CRC generator and computes the CRC for a sample message.

    // Using CRC-16/CCITT-0 Algorithm
    #define CRC_BITLEN          (16u)
    #define CRC_POLYNOMIAL      (0x1021u)
    #define CRC_LFSR_SEED       (0xffffu)
    #define CRC_DATA_REVERSE    (0u)
    #define CRC_DATA_XOR        (0u)
    #define CRC_REM_REVERSE     (0u)
    #define CRC_REM_XOR         (0x0000u)

    #define MSG_LENGTH 9

    CY_ALIGN(4) uint8_t message[MSG_LENGTH] = "123456789";
    CY_ALIGN(4) uint32_t calc_crc           = 0;

    // Set CRC algorithm parameters
    crc_algorithm_t my_algorithm =
    {
        .width         = CRC_BITLEN,
        .polynomial    = CRC_POLYNOMIAL,
        .lfsrInitState = CRC_LFSR_SEED,
        .dataReverse   = CRC_DATA_REVERSE,
        .dataXor       = CRC_DATA_XOR,
        .remReverse    = CRC_REM_REVERSE,
        .remXor        = CRC_REM_XOR
    };

    cy_rslt_t   rslt;
    cyhal_crc_t crc_obj;

    // Initialize the CRC Generator
    rslt = cyhal_crc_init(&crc_obj);

    // Initialize the CRC algorithm parameters
    rslt = cyhal_crc_start(&crc_obj, &my_algorithm);

    // Compute CRC
    rslt = cyhal_crc_compute(&crc_obj, message, MSG_LENGTH);

    // Finish computation
    rslt = cyhal_crc_finish(&crc_obj, &calc_crc);

    // Additional computations can be done here if needed

    // Release the CRC generator
    // Note: Free only if not required anymore
    cyhal_crc_free(&crc_obj);

API Reference
	CRC HAL Results
	CRC specific return codes.

Data Structures
struct	crc_algorithm_t
	CRC algorithm parameters. More...

Functions
cy_rslt_t	cyhal_crc_init (cyhal_crc_t *obj)
	Initialize the CRC generator. More...
void	cyhal_crc_free (cyhal_crc_t *obj)
	Release the CRC generator. More...
cy_rslt_t	cyhal_crc_start (cyhal_crc_t *obj, const crc_algorithm_t *algorithm)
	The CRC block is setup to perform CRC computation. More...
cy_rslt_t	cyhal_crc_compute (const cyhal_crc_t *obj, const uint8_t *data, size_t length)
	Computes the CRC for the given data and accumulates the CRC with the CRC generated from previous calls. More...
cy_rslt_t	cyhal_crc_finish (const cyhal_crc_t *obj, uint32_t *crc)
	Finalizes the CRC computation and returns the CRC for the complete set of data passed through a single call or multiple calls to cyhal_crc_compute. More...

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Data Structure Documentation

crc_algorithm_t

struct crc_algorithm_t

Data Fields
uint32_t	width	Bit width of the CRC.
uint32_t	polynomial	The polynomial to use.
uint32_t	lfsrInitState	Initial state of the LFSR.
uint32_t	dataXor	Byte mask to xor with the data.
uint32_t	remXor	Mask to xor with the remainder.
bool	dataReverse	The order in which data should be processed. If 0, data is processed MSB first. If 1, data is processed LSB first.
bool	remReverse	If 1, the remainder is reversed. If 0, it is not.

Function Documentation

cyhal_crc_init()

cy_rslt_t cyhal_crc_init

(

cyhal_crc_t *

obj

)

Initialize the CRC generator.

This function reserves the CRYPTO block for CRC calculations.

Parameters

[out]

obj

Pointer to a CRC generator object. The caller must allocate the memory for this object but the init function will initialize its contents.

Returns

The status of the init request.

Returns CY_RSLT_SUCCESS if the operation was successful. Refer Snippet1: CRC Generation for more information.

cyhal_crc_free()

void cyhal_crc_free

(

cyhal_crc_t *

obj

)

Release the CRC generator.

Parameters

[in,out]

obj

The CRC generator object

cyhal_crc_start()

cy_rslt_t cyhal_crc_start	(	cyhal_crc_t *	obj,
		const crc_algorithm_t *	algorithm
	)

The CRC block is setup to perform CRC computation.

Parameters

[in,out]	obj	The CRC generator object
[in]	algorithm	The CRC algorithm to use for computations Refer crc_algorithm_t.

Returns

The status of the compute request

Note

The state of the CRC Block will be reset to the state provided by in the argument algorithm.

Returns CY_RSLT_SUCCESS if the operation was successful.

cyhal_crc_compute()

cy_rslt_t cyhal_crc_compute	(	const cyhal_crc_t *	obj,
		const uint8_t *	data,
		size_t	length
	)

Computes the CRC for the given data and accumulates the CRC with the CRC generated from previous calls.

This function can be called multiple times to provide additional data.

Note

Input data must be 4-byte aligned. Refer Snippet1: CRC Generation for more details.

Parameters

[in]	obj	The CRC generator object
[in]	data	The input data
[in]	length	The number of bytes in the data

Returns

The status of the compute request

Returns CY_RSLT_SUCCESS if the operation was successful.

cyhal_crc_finish()

cy_rslt_t cyhal_crc_finish	(	const cyhal_crc_t *	obj,
		uint32_t *	crc
	)

Finalizes the CRC computation and returns the CRC for the complete set of data passed through a single call or multiple calls to cyhal_crc_compute.

Note

The computed CRC pointer provided must be 4 byte aligned. Refer to Snippet1: CRC Generation for more details.

If the length of the CRC is less than a full word, the result will be in the lower bits allowing the result to be downcast if desired.

Parameters

[in]	obj	The CRC generator object
[out]	crc	The computed CRC

Returns

The status of the compute request

Returns CY_RSLT_SUCCESS if the operation was successful.