MbedCRC< polynomial, width, mode_limit > Class Template Reference

CRC object provides CRC generation through hardware or software. More...

#include <MbedCRC.h>

Public Member Functions
constexpr	MbedCRC (uint32_t initial_xor, uint32_t final_xor, bool reflect_data, bool reflect_remainder)
	Lifetime of CRC object. More...
int32_t	compute (const void *buffer, crc_data_size_t size, uint32_t *crc)
	Compute CRC for the data input Compute CRC performs the initialization, computation and collection of final CRC. More...
int32_t	compute_partial (const void *buffer, crc_data_size_t size, uint32_t *crc)
	Compute partial CRC for the data input. More...
int32_t	compute_partial_start (uint32_t *crc)
	Compute partial start, indicate start of partial computation. More...
int32_t	compute_partial_stop (uint32_t *crc)
	Get the final CRC value of partial computation. More...

Static Public Member Functions
static constexpr uint32_t	get_polynomial ()
	Get the current CRC polynomial. More...
static constexpr uint8_t	get_width ()
	Get the current CRC width. More...

Detailed Description

template<uint32_t polynomial = POLY_32BIT_ANSI, uint8_t width = 32, CrcMode mode_limit = CrcMode::HARDWARE>
class MbedCRC< polynomial, width, mode_limit >

CRC object provides CRC generation through hardware or software.

CRC sums can be generated using three different methods: hardware, software ROM tables and bitwise computation. The mode used is normally selected automatically based on required polynomial and hardware capabilities. Any polynomial in standard form (x^3 + x + 1) can be used for computation, but custom ones can affect the performance.

First choice is the hardware mode. The supported polynomials are hardware specific, and you need to consult your MCU manual to discover them. Next, ROM polynomial tables are tried (you can find list of supported polynomials here crc_polynomial). If the selected configuration is supported, it will accelerate the software computations. If ROM tables are not available for the selected polynomial, then CRC is computed at run time bit by bit for all data input.

If desired, the mode can be manually limited for a given instance by specifying the mode_limit template parameter. This might be appropriate to ensure a table is not pulled in for a non-speed-critical CRC, or to avoid the hardware set-up overhead if you know you will be calling compute with very small data sizes.

Note

Synchronization level: Thread safe

Template Parameters

polynomial	CRC polynomial value in hex
width	CRC polynomial width
mode_limit	Maximum amount of acceleration to use

Example: Compute CRC data

#include "mbed.h"
 
int main() {
    MbedCRC<POLY_32BIT_ANSI, 32> ct;
 
    char  test[] = "123456789";
    uint32_t crc = 0;
 
    printf("\nPolynomial = 0x%lx  Width = %d \n", ct.get_polynomial(), ct.get_width());
 
    ct.compute((void *)test, strlen((const char*)test), &crc);
 
    printf("The CRC of data \"123456789\" is : 0x%lx\n", crc);
    return 0;
}

Example: Compute CRC with data available in parts

#include "mbed.h"
int main() {
    MbedCRC<POLY_32BIT_ANSI, 32> ct;
 
    char  test[] = "123456789";
    uint32_t crc = 0;
 
    printf("\nPolynomial = 0x%lx  Width = %d \n", ct.get_polynomial(), ct.get_width());
    ct.compute_partial_start(&crc);
    ct.compute_partial((void *)&test, 4, &crc);
    ct.compute_partial((void *)&test[4], 5, &crc);
    ct.compute_partial_stop(&crc);
    printf("The CRC of data \"123456789\" is : 0x%lx\n", crc);
    return 0;
}

Definition at line 155 of file MbedCRC.h.

Constructor & Destructor Documentation

MbedCRC()

constexpr MbedCRC ( uint32_t  initial_xor, uint32_t  final_xor, bool  reflect_data, bool  reflect_remainder  )

constexpr

Lifetime of CRC object.

Parameters

initial_xor	Initial value/seed to Xor
final_xor	Final Xor value
reflect_data
reflect_remainder

Note

Default constructor without any arguments is valid only for supported CRC polynomials. :: crc_polynomial_t MbedCRC <POLY_7BIT_SD, 7> ct; — Valid POLY_7BIT_SD MbedCRC <0x1021, 16> ct; — Valid POLY_16BIT_CCITT MbedCRC <POLY_16BIT_CCITT, 32> ct; — Invalid, compilation error MbedCRC <POLY_16BIT_CCITT, 32> ct (i,f,rd,rr) Constructor can be used for not supported polynomials MbedCRC<POLY_16BIT_CCITT, 16> sd(0, 0, false, false); Constructor can also be used for supported polynomials with different initial/final/reflect values

Definition at line 186 of file MbedCRC.h.

Member Function Documentation

compute()

int32_t compute	(	const void *	buffer,
		crc_data_size_t	size,
		uint32_t *	crc
	)

Compute CRC for the data input Compute CRC performs the initialization, computation and collection of final CRC.

Parameters

buffer	Data bytes
size	Size of data
crc	CRC is the output value

Returns

0 on success, negative error code on failure

Definition at line 229 of file MbedCRC.h.

compute_partial()

int32_t compute_partial	(	const void *	buffer,
		crc_data_size_t	size,
		uint32_t *	crc
	)

Compute partial CRC for the data input.

CRC data if not available fully, CRC can be computed in parts with available data.

In case of hardware, intermediate values and states are saved by hardware. Mutex locking is used to serialize access to hardware CRC.

In case of software CRC, previous CRC output should be passed as argument to the current compute_partial call. Please note the intermediate CRC value is maintained by application and not the driver.

Precondition

: Call compute_partial_start to start the partial CRC calculation.

Postcondition

: Call compute_partial_stop to get the final CRC value.

Parameters

buffer	Data bytes
size	Size of data
crc	CRC value is intermediate CRC value filled by API.

Returns

0 on success or a negative error code on failure

Note

: CRC as output in compute_partial is not final CRC value, call compute_partial_stop to get final correct CRC value.

Definition at line 255 of file MbedCRC.h.

compute_partial_start()

int32_t compute_partial_start

(

uint32_t *

crc

)

Compute partial start, indicate start of partial computation.

This API should be called before performing any partial computation with compute_partial API.

Parameters

crc	Initial CRC value set by the API

Returns

0 on success or a negative in case of failure

Note

: CRC is an out parameter and must be reused with compute_partial and compute_partial_stop without any modifications in application.

Definition at line 270 of file MbedCRC.h.

compute_partial_stop()

int32_t compute_partial_stop

(

uint32_t *

crc

)

Get the final CRC value of partial computation.

CRC value available in partial computation is not correct CRC, as some algorithms require remainder to be reflected and final value to be XORed This API is used to perform final computation to get correct CRC value.

Parameters

crc	CRC result

Returns

0 on success or a negative in case of failure.

Definition at line 284 of file MbedCRC.h.

get_polynomial()

static constexpr uint32_t get_polynomial ( )

staticconstexpr

Get the current CRC polynomial.

Returns

Polynomial value

Definition at line 293 of file MbedCRC.h.

get_width()

static constexpr uint8_t get_width ( )

staticconstexpr

Get the current CRC width.

Returns

CRC width

Definition at line 302 of file MbedCRC.h.