Collaboration diagram for CRC driver:

Data Structures
struct	crc_config_t
	CRC protocol configuration. 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)
	Enable and configure the CRC peripheral module. More...

static void	CRC_Deinit (CRC_Type *base)
	Disable 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)
	Write data to the CRC module. More...

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

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

Usage Information

This section describes the programming interface of the CRC driver.

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 confiration 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);

Data Structure Documentation

struct crc_config_t

CRC protocol configuration.

This structure holds the configuration for the CRC protocol.

Data Fields
bool	complementChecksum	True if the result shall be complement of the actual checksum.
crc_bits_t	crcBits	Selects 16- or 32- bit CRC protocol.
crc_result_t	crcResult	Selects final or intermediate checksum return from CRC_Get16bitResult() or CRC_Get32bitResult()
uint32_t	polynomial	CRC Polynomial, MSBit first. Example polynomial: 0x1021 = 1_0000_0010_0001 = x^12+x^5+1
bool	reflectIn	Reflect bits on input.
bool	reflectOut	Reflect bits on output.
uint32_t	seed	Starting checksum value

Enumeration Type Documentation

enum crc_bits_t

CRC bit width.

Enumerator
kCrcBits32	Generate 16-bit CRC code

enum crc_result_t

CRC result type.

Enumerator
kCrcIntermediateChecksum	CRC data register read value is the final checksum. Reflect out and final xor protocol features are applied.

Function Documentation

static void CRC_Deinit ( CRC_Type * base )

inlinestatic

Disable the CRC peripheral module.

This functions disables the clock gate in the Kinetis SIM module for the CRC peripheral.

Parameters

base	CRC peripheral address.

uint16_t CRC_Get16bitResult ( CRC_Type * base )

Read 16-bit checksum from the CRC module.

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.

static uint32_t CRC_Get32bitResult ( CRC_Type * base )

inlinestatic

Read 32-bit checksum from the CRC module.

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.

void CRC_GetDefaultConfig ( crc_config_t * config )

Loads default values to CRC protocol configuration structure.

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_Init	(	CRC_Type *	base,
		const crc_config_t *	config
	)

Enable and configure the CRC peripheral module.

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

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

Write data to the CRC module.

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.

Data Structures

Enumerations

Functions

Usage Information

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

Data Structure Documentation

Enumeration Type Documentation

Function Documentation