CRC Peripheral and Driver Overview

Content including 1) peripheral features, work logic and work method; 2) driver design logic and use method; 3) typical use case. More...

Peripheral features

The Cyclic Redundancy Check (CRC) generator module uses the 16-bit CRC-CCITT polynomial, x16 + x12 + x5 + 1, to generate a CRC code for error detection.

 Features

  + The CRC module calculates 8 bits at a time with a 16-bit code, and provides checks on all access locations,   *    whether they are in simple data or simply provided in RAM.  *    - Hardware CRC generator circuit using 16-bit shift register.  *    - CRC16-CCITT compliancy with x16 + x12 + x5 + 1 polynomial.  *    - Programmable initial seed value.  *  *  + Optional ability to transpose input data and CRC result via transpose register, required on applications where bytes are in LSb (Least Significant bit) format.  *  *  + This section defines the CRC operation in run, wait, and stop modes.  *    - Run Mode and Wait Mode is the basic mode of operation.  *

How this driver is designed to make this peripheral work

This driver provides multiple definitions/functions to enable and configure the CRC peripheral module. The CRC_Init() function takes the argument in type of crc_config_t, which contains all CRC features. After all the necessary configuration is completed, the data for error detection can be written, then the CRC checksum value will be stored in the CRC data register.The APIs this driver provides can be classified in 3 API groups:

• Initialization and De-initialization Interfaces
  • Functions to initialize or de-initialize the CRC module.
  • Configure the CRC to certain state with all feature covered.
• CRC Configuration Interfaces -This function group is used to separately configure other parameters required for CRC calculation.
• CRC Write/Read Data Interfaces
  • The CRC Data register contains the value of the seed, data, and checksum. The APIs in this function group can be used to write the value of the seed and the data for error detection, reads the 16-bit checksum from the CRC module.

How to use this driver

• Firstly initialize CRC module with CRC_Init. In this step, you can optionally set the seed value by configure crc_config_t::bSetSeed and crc_config_t::u16CrcSeedValue.
• If CRC_Init has set the seed value, you can call CRC_WriteData directly, and CRC module will calculate the CRC result. If CRC_Init does not set the seed value, then CRC_SetSeedValue should be called before CRC_WriteData.
• Call CRC_Get16bitResult to get the CRC result.
• To start a new CRC calculation, call CRC_SetSeedValue first, then CRC_WriteData to feed data, and finally CRC_Get16bitResult to read result.

Typical Use Case

• CRC Initialization:
  • Initialization with seed, set seed value by configuring sConfig.

    char testData[]  = "123456789";
    crc_config_t sConfig;
    uint16_t checksum16;
    
    CRC_GetDefaultConfig(&sConfig);
    sConfig.bSetSeed = true;
    sConfig.u16CrcSeedValue = kCRC_Crc16CCITT;
    
    CRC_Init(CRC, &sConfig);
    CRC_WriteData(CRC, (uint8_t *)&testData[0], sizeof(testData) - 1, false);
    checksum16 = CRC_Get16bitResult(CRC, false);

  • Initialization without seed, get seed value by call CRC_SetSeedValue.

    char testData[]  = "123456789";
    crc_config_t sConfig;
    uint16_t checksum16;
    
    CRC_GetDefaultConfig(&sConfig);
    sConfig.bSetSeed = false;
    
    CRC_Init(CRC, &sConfig);
    CRC_SetSeedValue(CRC, kCRC_Crc16CCITT);
    CRC_WriteData(CRC, (uint8_t *)&testData[0], sizeof(testData) - 1, false);
    checksum16 = CRC_Get16bitResult(CRC, false);

• Calculate CRC for multiple data array.

           uint8_t testData1[] = {'a', 'b', 'c', 'd'};
           uint8_t testData2[] = {'A', 'B', 'C', 'D'};
           uint16_t crcResult1;
           uint16_t crcResult2;
  
           CRC_SetSeedValue(CRC, kCRC_Crc16Kermit);
           CRC_WriteData(CRC, testData1, sizeof(testData1), true);
           crcResult1 = CRC_Get16bitResult(CRC, true);
  
           CRC_SetSeedValue(CRC, kCRC_Crc16Kermit);
           CRC_WriteData(CRC, testData2, sizeof(testData2), true);
           crcResult2 = CRC_Get16bitResult(CRC, true);
  *