Overview

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

The cyclic redundancy check (CRC) module generates 16/32-bit CRC code for error detection. The CRC module provides a programmable polynomial, 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 gate for the CRC module in the Kinetis SIM module and fully (re-)configures the CRC module according to configuration structure. 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_Get16bitResult() or CRC_Get32bitResult() 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. The crcResult member of configuration structure determines if CRC_Get16bitResult() or CRC_Get32bitResult() return value is final checksum or intermediate checksum. 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/CCIT-FALSE protocol.

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 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 data register. Depending on prior CRC module usage the return value is either intermediate checksum or final checksum. Example: for 16-bit CRCs the following call sequences can be used:

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_Get16bitResult() to get intermediate checksum.

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

Comments about API usage in RTOS

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

The triplets

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

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;

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/CCIT-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/CCIT-FALSE */
CRC_Init(base, &config);
CRC_WriteData(base, data, sizeof(data));
checksum = CRC_Get16bitResult(base);

Simple example with CRC-32 protocol configuration

crc_config_t config;
uint32_t checksum;
config.polynomial = 0x04C11DB7u;
config.seed = 0xFFFFFFFFu;
config.crcBits = kCrcBits32;
config.reflectIn = true;
config.reflectOut = true;
config.complementChecksum = true;
config.crcResult = kCrcFinalChecksum;
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);

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 module init functions for 3 different protocols: CRC-16 (ARC), CRC-16/CCIT-FALSE and CRC-32. Table below lists the individual protocol specifications. See also: http://reveng.sourceforge.net/crc-catalogue/

	CRC-16/CCIT-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 init functions:

void InitCrc16_CCIT(CRC_Type *base, uint32_t seed, bool isLast)
{
    crc_config_t config;
    config.polynomial = 0x1021;
    config.seed = seed;
    config.reflectIn = false;
    config.reflectOut = false;
    config.complementChecksum = false;
    config.crcBits = kCrcBits16;
    config.crcResult = isLast?kCrcFinalChecksum:kCrcIntermediateChecksum;
    CRC_Init(base, &config);
}
void InitCrc16(CRC_Type *base, uint32_t seed, bool isLast)
{
    crc_config_t config;
    config.polynomial = 0x8005;
    config.seed = seed;
    config.reflectIn = true;
    config.reflectOut = true;
    config.complementChecksum = false;
    config.crcBits = kCrcBits16;
    config.crcResult = isLast?kCrcFinalChecksum:kCrcIntermediateChecksum;
    CRC_Init(base, &config);
}
void InitCrc32(CRC_Type *base, uint32_t seed, bool isLast)
{
    crc_config_t config;
    config.polynomial = 0x04C11DB7U;
    config.seed = seed;
    config.reflectIn = true;
    config.reflectOut = true;
    config.complementChecksum = true;
    config.crcBits = kCrcBits32;
    config.crcResult = isLast?kCrcFinalChecksum:kCrcIntermediateChecksum;
    CRC_Init(base, &config);
}

The following context switches show possible API usage:

uint16_t checksumCrc16;
uint32_t checksumCrc32;
uint16_t checksumCrc16Ccit;
checksumCrc16 = 0x0;
checksumCrc32 = 0xFFFFFFFFU;
checksumCrc16Ccit = 0xFFFFU;
/* Task A bytes[0-3] */
InitCrc16(base, checksumCrc16, false);
CRC_WriteData(base, &data[0], 4);
checksumCrc16 = CRC_Get16bitResult(base);
/* Task B bytes[0-3] */
InitCrc16_CCIT(base, checksumCrc16Ccit, false);
CRC_WriteData(base, &data[0], 4);
checksumCrc16Ccit = CRC_Get16bitResult(base);
/* Task C 4 bytes[0-3] */
InitCrc32(base, checksumCrc32, false);
CRC_WriteData(base, &data[0], 4);
checksumCrc32 = CRC_Get32bitResult(base);
/* Task B add final 5 bytes[4-8] */
InitCrc16_CCIT(base, checksumCrc16Ccit, true);
CRC_WriteData(base, &data[4], 5);
checksumCrc16Ccit = CRC_Get16bitResult(base);
/* Task C 3 bytes[4-6] */
InitCrc32(base, checksumCrc32, false);
CRC_WriteData(base, &data[4], 3);
checksumCrc32 = CRC_Get32bitResult(base);
/* Task A 3 bytes[4-6] */
InitCrc16(base, checksumCrc16, false);
CRC_WriteData(base, &data[4], 3);
checksumCrc16 = CRC_Get16bitResult(base);
/* Task C add final 2 bytes[7-8] */
InitCrc32(base, checksumCrc32, true);
CRC_WriteData(base, &data[7], 2);
checksumCrc32 = CRC_Get32bitResult(base);
/* Task A add final 2 bytes[7-8] */
InitCrc16(base, checksumCrc16, true);
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_CCIT_FALSE_AS_DEFAULT 1
	Default configuration structure filled by CRC_GetDefaultConfig(). More...

Enumerations
enum	crc_bits_t { kCrcBits16 = 0U, kCrcBits32 = 1U }
	CRC bit width. More...

enum	crc_result_t { kCrcFinalChecksum = 0U, kCrcIntermediateChecksum = 1U }
	CRC result type. 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_GetDefaultConfig (crc_config_t *config)
	Loads default values 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...

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, 0))
	CRC driver version. More...

Data Structure Documentation

struct crc_config_t

This structure holds the configuration for the CRC protocol.

Data Fields
uint32_t	polynomial
	CRC Polynomial, MSBit first. More...

uint32_t	seed
	Starting checksum value.

bool	reflectIn
	Reflect bits on input. More...

bool	reflectOut
	Reflect bits on output. More...

bool	complementChecksum
	True if the result shall be complement of the actual checksum. More...

crc_bits_t	crcBits
	Selects 16- or 32- bit CRC protocol. More...

crc_result_t	crcResult
	Selects final or intermediate checksum return from CRC_Get16bitResult() or CRC_Get32bitResult()

Field Documentation

uint32_t crc_config_t::polynomial

Example polynomial: 0x1021 = 1_0000_0010_0001 = x^12+x^5+1

bool crc_config_t::reflectIn

bool crc_config_t::reflectOut

bool crc_config_t::complementChecksum

crc_bits_t crc_config_t::crcBits

Macro Definition Documentation

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

Version 2.0.0.

#define CRC_DRIVER_USE_CRC16_CCIT_FALSE_AS_DEFAULT 1

Use CRC16-CCIT-FALSE as defeault.

Enumeration Type Documentation

enum crc_bits_t

Enumerator
kCrcBits16	Generate 16-bit CRC code.
kCrcBits32	Generate 32-bit CRC code.

enum crc_result_t

Enumerator

kCrcFinalChecksum

CRC data register read value is the final checksum.

Reflect out and final xor protocol features are applied.

kCrcIntermediateChecksum

CRC data register read value is intermediate checksum (raw value).

Reflect out and final xor protocol feature are not applied. Intermediate checksum can be used as a seed for CRC_Init() to continue adding data to this checksum.

Function Documentation

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

This functions enables the clock gate in the Kinetis SIM module for the CRC peripheral. It also configures the CRC module 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 clock gate in the Kinetis SIM module for the CRC peripheral.

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 = 0x1021;
config->seed = 0xFFFF;
config->reflectIn = false;
config->reflectOut = false;
config->complementChecksum = false;
config->crcBits = kCrcBits16;
config->crcResult = kCrcFinalChecksum;

Parameters

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. The configured type of transpose is applied.

Parameters

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

static uint32_t CRC_Get32bitResult ( CRC_Type * base )

inlinestatic

Reads CRC data register (intermediate or final checksum). The configured type of transpose and complement are applied.

Parameters

base	CRC peripheral address.

Returns: intermediate or final 32-bit checksum, after configured transpose and complement operations.

uint16_t CRC_Get16bitResult ( CRC_Type * base )

Reads CRC data register (intermediate or final checksum). The configured type of transpose and complement are applied.

Parameters

base	CRC peripheral address.

Returns: intermediate or final 16-bit checksum, after configured transpose 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