Overview

MCUXpresso SDK provides the Peripheral driver for the Cyclic Redundancy Check (CRC) module of MCUXpresso SDK devices.

The cyclic redundancy check (CRC) module generates 16/32-bit CRC code for error detection. The CRC module provides three variants of polynomials, a programmable seed and other parameters required to implement a 16-bit or 32-bit CRC standard.

CRC Driver Initialization and Configuration

CRC_Init() function enables the clock for the CRC module in the LPC SYSCON block and fully (re-)configures the CRC module according to configuration structure. It also starts checksum computation by writing the seed.

The seed member of the configuration structure is the initial checksum for which new data can be added to. When starting new checksum computation, the seed shall be set to the initial checksum per the CRC protocol specification. For continued checksum operation, the seed shall be set to the intermediate checksum value as obtained from previous calls to CRC_GetConfig() function. After CRC_Init(), one or multiple CRC_WriteData() calls follow to update checksum with data, then CRC_Get16bitResult() or CRC_Get32bitResult() follows to read the result. CRC_Init() can be called as many times as required, thus, allows for runtime changes of CRC protocol.

CRC_GetDefaultConfig() function can be used to set the module configuration structure with parameters for CRC-16/CCITT-FALSE protocol.

CRC_Deinit() function disables clock to the CRC module.

CRC_Reset() performs hardware reset of the CRC module.

CRC Write Data

The CRC_WriteData() function is used to add data to actual CRC. Internally it tries to use 32-bit reads and writes for all aligned data in the user buffer and it uses 8-bit reads and writes for all unaligned data in the user buffer. This function can update CRC with user supplied data chunks of arbitrary size, so one can update CRC byte by byte or with all bytes at once. Prior call of CRC configuration function CRC_Init() fully specifies the CRC module configuration for CRC_WriteData() call.

CRC Get Checksum

The CRC_Get16bitResult() or CRC_Get32bitResult() function is used to read the CRC module checksum register. The bit reverse and 1's complement operations are already applied to the result if previously configured. Use CRC_GetConfig() function to get the actual checksum without bit reverse and 1's complement applied so it can be used as seed when resuming calculation later.

CRC_Init() / CRC_WriteData() / CRC_Get16bitResult() to get final checksum.

CRC_Init() / CRC_WriteData() / ... / CRC_WriteData() / CRC_Get16bitResult() to get final checksum.

CRC_Init() / CRC_WriteData() / CRC_GetConfig() to get intermediate checksum to be used as seed value in future.

CRC_Init() / CRC_WriteData() / ... / CRC_WriteData() / CRC_GetConfig() to get intermediate checksum.

Comments about API usage in RTOS

If multiple RTOS tasks share the CRC module to compute checksums with different data and/or protocols, the following needs to be implemented by the user:

The triplets

CRC_Init() / CRC_WriteData() / CRC_Get16bitResult() or CRC_Get32bitResult() or CRC_GetConfig()

shall be protected by RTOS mutex to protect CRC module against concurrent accesses from different tasks. Example:

CRC_Module_RTOS_Mutex_Lock;
CRC_Init();
CRC_WriteData();
CRC_Get16bitResult();
CRC_Module_RTOS_Mutex_Unlock;

Alternatively, the context switch handler could read original configuration and restore it when switching back to original task/thread:

CRC_GetConfig(base, &originalConfig);
/* ... other task using CRC engine... */
CRC_Init(base, &originalConfig);

Comments about API usage in interrupt handler

All APIs can be used from interrupt handler although execution time shall be considered (interrupt latency of equal and lower priority interrupts increases). Protection against concurrent accesses from different interrupt handlers and/or tasks shall be assured by the user.

CRC Driver Examples

Simple examples

Simple example with default CRC-16/CCITT-FALSE protocol

crc_config_t config;
CRC_Type *base;
uint8_t data[] = {0x00, 0x01, 0x02, 0x03, 0x04};
uint16_t checksum;
base = CRC0;
CRC_GetDefaultConfig(base, &config); /* default gives CRC-16/CCITT-FALSE */
CRC_Init(base, &config);
CRC_WriteData(base, data, sizeof(data));
checksum = CRC_Get16bitResult(base);
CRC_Deinit(base);

Simple example with CRC-32 protocol configuration

crc_config_t config;
uint32_t checksum;
config.polynomial = kCRC_Polynomial_CRC_32;
config.reverseIn = true;
config.complementIn = false;
config.reverseOut = true;
config.complementOut = true;
config.seed = 0xFFFFFFFFu;
CRC_Init(base, &config);
/* example: update by 1 byte at time */
while (dataSize)
{
    uint8_t c = GetCharacter();
    CRC_WriteData(base, &c, 1);
    dataSize--;
}
checksum = CRC_Get32bitResult(base);
CRC_Deinit(base);

Advanced examples

Per-partes data updates with context switch between. Assuming we have 3 tasks/threads, each using CRC module to compute checksums of different protocol, with context switches.

Firstly, we prepare 3 CRC configurations for 3 different protocols: CRC-16 (ARC), CRC-16/CCITT-FALSE and CRC-32. Table below lists the individual protocol specifications. See also: http://reveng.sourceforge.net/crc-catalogue/

	CRC-16/CCITT-FALSE	CRC-16	CRC-32
Width	16 bits	16 bits	32 bits
Polynomial	0x1021	0x8005	0x04C11DB7
Initial seed	0xFFFF	0x0000	0xFFFFFFFF
Complement checksum	No	No	Yes
Reflect In	No	Yes	Yes
Reflect Out	No	Yes	Yes

Corresponding functions to get configurations:

void GetConfigCrc16Ccitt(CRC_Type *base, crc_config_t *config)
{
    config->polynomial = kCRC_Polynomial_CRC_CCITT;
    config->reverseIn = false;
    config->complementIn = false;
    config->reverseOut = false;
    config->complementOut = false;
    config->seed = 0xFFFFU;
}
void GetConfigCrc16(CRC_Type *base, crc_config_t *config)
{
    config->polynomial = kCRC_Polynomial_CRC_16;
    config->reverseIn = true;
    config->complementIn = false;
    config->reverseOut = true;
    config->complementOut = false;
    config->seed = 0x0U;
}
void GetConfigCrc32(CRC_Type *base, crc_config_t *config)
{
    config->polynomial = kCRC_Polynomial_CRC_32;
    config->reverseIn = true;
    config->complementIn = false;
    config->reverseOut = true;
    config->complementOut = true;
    config->seed = 0xFFFFFFFFU;
}

The following context switches show possible API usage:

uint16_t checksumCrc16;
uint32_t checksumCrc32;
uint16_t checksumCrc16Ccitt;
crc_config_t configCrc16;
crc_config_t configCrc32;
crc_config_t configCrc16Ccitt;
GetConfigCrc16(base, &configCrc16);
GetConfigCrc32(base, &configCrc32);
GetConfigCrc16Ccitt(base, &configCrc16Ccitt);
/* Task A bytes[0-3] */    
CRC_Init(base, &configCrc16);
CRC_WriteData(base, &data[0], 4);
CRC_GetConfig(base, &configCrc16);
/* Task B bytes[0-3] */
CRC_Init(base, &configCrc16Ccitt);
CRC_WriteData(base, &data[0], 4);
CRC_GetConfig(base, &configCrc16Ccitt);
/* Task C 4 bytes[0-3] */
CRC_Init(base, &configCrc32);
CRC_WriteData(base, &data[0], 4);
CRC_GetConfig(base, &configCrc32);
/* Task B add final 5 bytes[4-8] */
CRC_Init(base, &configCrc16Ccitt);
CRC_WriteData(base, &data[4], 5);
checksumCrc16Ccitt = CRC_Get16bitResult(base);
/* Task C 3 bytes[4-6] */
CRC_Init(base, &configCrc32);
CRC_WriteData(base, &data[4], 3);
CRC_GetConfig(base, &configCrc32);
/* Task A 3 bytes[4-6] */
CRC_Init(base, &configCrc16);
CRC_WriteData(base, &data[4], 3);
CRC_GetConfig(base, &configCrc16);
/* Task C add final 2 bytes[7-8] */
CRC_Init(base, &configCrc32);
CRC_WriteData(base, &data[7], 2);
checksumCrc32 = CRC_Get32bitResult(base);
/* Task A add final 2 bytes[7-8] */
CRC_Init(base, &configCrc16);
CRC_WriteData(base, &data[7], 2);
checksumCrc16 = CRC_Get16bitResult(base);

Files
file	fsl_crc.h

Data Structures
struct	crc_config_t
	CRC protocol configuration. More...

Macros
#define	CRC_DRIVER_USE_CRC16_CCITT_FALSE_AS_DEFAULT 1
	Default configuration structure filled by CRC_GetDefaultConfig(). More...

Enumerations
enum	crc_polynomial_t { kCRC_Polynomial_CRC_CCITT = 0U, kCRC_Polynomial_CRC_16 = 1U, kCRC_Polynomial_CRC_32 = 2U }
	CRC polynomials to use. More...

Functions
void	CRC_Init (CRC_Type base, const crc_config_t config)
	Enables and configures the CRC peripheral module. More...

static void	CRC_Deinit (CRC_Type *base)
	Disables the CRC peripheral module. More...

void	CRC_Reset (CRC_Type *base)
	resets CRC peripheral module. More...

void	CRC_GetDefaultConfig (crc_config_t *config)
	Loads default values to CRC protocol configuration structure. More...

void	CRC_GetConfig (CRC_Type base, crc_config_t config)
	Loads actual values configured in CRC peripheral to CRC protocol configuration structure. More...

void	CRC_WriteData (CRC_Type base, const uint8_t data, size_t dataSize)
	Writes data to the CRC module. More...

static uint32_t	CRC_Get32bitResult (CRC_Type *base)
	Reads 32-bit checksum from the CRC module. More...

static uint16_t	CRC_Get16bitResult (CRC_Type *base)
	Reads 16-bit checksum from the CRC module. More...

Driver version
#define	FSL_CRC_DRIVER_VERSION (MAKE_VERSION(2, 0, 1))
	CRC driver version. More...

Data Structure Documentation

struct crc_config_t

This structure holds the configuration for the CRC protocol.

Data Fields
crc_polynomial_t	polynomial
	CRC polynomial. More...

bool	reverseIn
	Reverse bits on input. More...

bool	complementIn
	Perform 1's complement on input. More...

bool	reverseOut
	Reverse bits on output. More...

bool	complementOut
	Perform 1's complement on output. More...

uint32_t	seed
	Starting checksum value. More...

Field Documentation

crc_polynomial_t crc_config_t::polynomial

bool crc_config_t::reverseIn

bool crc_config_t::complementIn

bool crc_config_t::reverseOut

bool crc_config_t::complementOut

uint32_t crc_config_t::seed

Macro Definition Documentation

#define FSL_CRC_DRIVER_VERSION (MAKE_VERSION(2, 0, 1))

Version 2.0.1.

Current version: 2.0.1

Change log:

Version 2.0.0
- initial version
Version 2.0.1
- add explicit type cast when writing to WR_DATA

#define CRC_DRIVER_USE_CRC16_CCITT_FALSE_AS_DEFAULT 1

Uses CRC-16/CCITT-FALSE as default.

Enumeration Type Documentation

enum crc_polynomial_t

Enumerator
kCRC_Polynomial_CRC_CCITT	x^16+x^12+x^5+1
kCRC_Polynomial_CRC_16	x^16+x^15+x^2+1
kCRC_Polynomial_CRC_32	x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1

Function Documentation

void CRC_Init	(	CRC_Type *	base,
		const crc_config_t *	config
	)

This functions enables the CRC peripheral clock in the LPC SYSCON block. It also configures the CRC engine and starts checksum computation by writing the seed.

Parameters

base	CRC peripheral address.
config	CRC module configuration structure.

static void CRC_Deinit ( CRC_Type * base )

inlinestatic

This functions disables the CRC peripheral clock in the LPC SYSCON block.

Parameters

base	CRC peripheral address.

void CRC_Reset ( CRC_Type * base )

Parameters

base	CRC peripheral address.

void CRC_GetDefaultConfig ( crc_config_t * config )

Loads default values to CRC protocol configuration structure. The default values are:

*   config->polynomial = kCRC_Polynomial_CRC_CCITT;
*   config->reverseIn = false;
*   config->complementIn = false;
*   config->reverseOut = false;
*   config->complementOut = false;
*   config->seed = 0xFFFFU;
* 

Parameters

config CRC protocol configuration structure

void CRC_GetConfig	(	CRC_Type *	base,
		crc_config_t *	config
	)

The values, including seed, can be used to resume CRC calculation later.

Parameters

base	CRC peripheral address.
config	CRC protocol configuration structure

void CRC_WriteData	(	CRC_Type *	base,
		const uint8_t *	data,
		size_t	dataSize
	)

Writes input data buffer bytes to CRC data register.

Parameters

base	CRC peripheral address.
data	Input data stream, MSByte in data[0].
dataSize	Size of the input data buffer in bytes.

static uint32_t CRC_Get32bitResult ( CRC_Type * base )

inlinestatic

Reads CRC data register.

Parameters

base	CRC peripheral address.

Returns: final 32-bit checksum, after configured bit reverse and complement operations.

static uint16_t CRC_Get16bitResult ( CRC_Type * base )

inlinestatic

Reads CRC data register.

Parameters

base	CRC peripheral address.

Returns: final 16-bit checksum, after configured bit reverse and complement operations.

Overview

CRC Driver Initialization and Configuration

CRC Write Data

CRC Get Checksum

Comments about API usage in RTOS

Comments about API usage in interrupt handler

CRC Driver Examples

Simple examples

Advanced examples

Files

Data Structures

Macros

Enumerations

Functions

Driver version

Data Structure Documentation

Data Fields

Field Documentation

Macro Definition Documentation

Enumeration Type Documentation

Function Documentation