This post was last edited by chenbingjy on 2023-6-5 10:49
huo_hu posted on 2023-6-5 09:11 The results of the lowest 8 bits of the 32-bit check are the same as those of the 8-bit check. I remember that the value of the polynomial of stm32 cannot be changed, so it cannot be suitable for all...
Thank you! I found a CRC calculator on the Internet that can customize the 8-bit polynomial and can calculate the correct result.
Then, I wrote the software calculation program in C language.
But there is also a 7-bit CRC calculation program:
#include "main.h"
/** @addtogroup STM32L4xx_HAL_Examples
* @{
*/
/** @addtogroup CRC_Bytes_Stream_7bit_CRC
* @{
*/
/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
#define BUFFER_SIZE_5 5 /* CRC7_DATA8_TEST5[] is 5-byte long */
#define BUFFER_SIZE_17 17 /* CRC7_DATA8_TEST17[] is 17-byte long */
#define BUFFER_SIZE_1 1 /* CRC7_DATA8_TEST1[] is 1-byte long */
#define BUFFER_SIZE_2 2 /* CRC7_DATA8_TEST2[] is 2-byte long */
/* User-defined polynomial */
//#define CRC_POLYNOMIAL_7B 0x65 /* X^7 + X^6 + X^5 + X^2 + 1,
// used in Train Communication Network, IEC 60870-5[17] */
#define CRC_POLYNOMIAL_7B 0x65 /* X^7 + X^6 + X^5 + X^2 + 1,*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
/* CRC handler declaration */
CRC_HandleTypeDef CrcHandle;
/* Used for storing CRC Value */
__IO uint32_t uwCRCValue = 0;
/* Bytes buffers that will consecutively yield CRCs */
static const uint8_t CRC7_DATA8_TEST5[5] = {0x12,0x34,0xBA,0x71,0xAD};
static const uint8_t CRC7_DATA8_TEST17[17] = {0x12,0x34,0xBA,0x71,0xAD,
0x11,0x56,0xDC,0x88,0x1B,
0xEE,0x4D,0x82, 0x93,0xA6,
0x7F,0xC3};
static const uint8_t CRC7_DATA8_TEST1[1] = {0x19};
static const uint8_t CRC7_DATA8_TEST2[2] = {0xAB,0xCD};
/* Expected CRC Values */
/* The 7 LSB bits are the 7-bit long CRC */
uint32_t uwExpectedCRCValue_1 = 0x00000057; /* First byte stream CRC */
uint32_t uwExpectedCRCValue_2 = 0x0000006E; /* Second byte stream CRC */
uint32_t uwExpectedCRCValue_3 = 0x0000004B; /* Third byte stream CRC */
uint32_t uwExpectedCRCValue_4 = 0x00000026; /* Fourth byte stream CRC */
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void Error_Handler(void);
/* Private functions ---------------------------------------------------------*/
/**
* @brief Main program
* @param None
* @retval None
*/
int main(void)
{
/* STM32L4xx HAL library initialization:
- Configure the Flash prefetch
- Systick timer is configured by default as source of time base, but user
can eventually implement his proper time base source (a general purpose
timer for example or other time source), keeping in mind that Time base
duration should be kept 1ms since PPP_TIMEOUT_VALUEs are defined and
handled in milliseconds basis.
- Set NVIC Group Priority to 4
- Low Level Initialization
*/
HAL_Init();
/* Configure the system clock to 120 MHz */
SystemClock_Config();
/* Configure LED1 and LED3 */
BSP_LED_Init(LED1);
BSP_LED_Init(LED3);
/****************************************************************************/
/* */
/* CRC peripheral initialization */
/* */
/****************************************************************************/
CrcHandle.Instance = CRC;
/* The default polynomial is not used. The one to be used must be defined
in CrcHandle.Init.GeneratingPolynomial */
CrcHandle.Init.DefaultPolynomialUse = DEFAULT_POLYNOMIAL_DISABLE;
/* Set the value of the generating polynomial.
The one used in that example is the 7-bit long CRC generating
polynomial X^7 + X^6 + X^5 + X^2 + 1 */
CrcHandle.Init.GeneratingPolynomial = CRC_POLYNOMIAL_7B;
/* The user-defined generating polynomial yields a 7-bit long CRC */
CrcHandle.Init.CRCLength = CRC_POLYLENGTH_7B;
/* The default init value is used */
CrcHandle.Init.DefaultInitValueUse = DEFAULT_INIT_VALUE_ENABLE;
/* The input data are not inverted */
CrcHandle.Init.InputDataInversionMode = CRC_INPUTDATA_INVERSION_NONE;
/* The output data are not inverted */
CrcHandle.Init.OutputDataInversionMode = CRC_OUTPUTDATA_INVERSION_DISABLE;
/* The input data are bytes (8-bit long data) */
CrcHandle.InputDataFormat = CRC_INPUTDATA_FORMAT_BYTES;
/* De-initialize the CRC peripheral */
if (HAL_CRC_DeInit(&CrcHandle) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/* Then, initialize the CRC handle */
if (HAL_CRC_Init(&CrcHandle) != HAL_OK)
{
/* Initialization Error */
Error_Handler();
}
/****************************************************************************/
/* */
/* CRC computation of a first bytes stream */
/* */
/****************************************************************************/
/* The 7-bit long CRC of a 5-byte buffer is computed. After peripheral initialization,
the CRC calculator is initialized with the default value that is 0x7F for
a 7-bit CRC.
The computed CRC is stored in uint32_t uwCRCValue. The 7-bit long CRC is made of
uwCRCValue 7 LSB bits. */
uwCRCValue = HAL_CRC_Accumulate(&CrcHandle, (uint32_t *)&CRC7_DATA8_TEST5, BUFFER_SIZE_5);
/* Compare the CRC value to the expected one */
if (uwCRCValue != uwExpectedCRCValue_1)
{
/* Wrong CRC value: Turn LED3 on */
Error_Handler();
}
/****************************************************************************/
/* */
/* CRC computation of a second bytes stream */
/* */
/****************************************************************************/
/* The 7-bit long CRC of a 17-byte buffer is computed. The CRC calculator
is not re-initialized, instead the previously computed CRC is used
as initial value. */
uwCRCValue = HAL_CRC_Accumulate(&CrcHandle, (uint32_t *)&CRC7_DATA8_TEST17, BUFFER_SIZE_17);
/* Compare the CRC value to the expected one */
if (uwCRCValue != uwExpectedCRCValue_2)
{
/* Wrong CRC value: Turn LED3 on */
Error_Handler();
}
/****************************************************************************/
/* */
/* CRC computation of a single byte */
/* */
/****************************************************************************/
/* The 7-bit long CRC of a 1-byte buffer is computed. The CRC calculator
is not re-initialized, instead the previously computed CRC is used
as initial value. */
uwCRCValue = HAL_CRC_Accumulate(&CrcHandle, (uint32_t *)&CRC7_DATA8_TEST1, BUFFER_SIZE_1);
/* Compare the CRC value to the expected one */
if (uwCRCValue != uwExpectedCRCValue_3)
{
/* Wrong CRC value: Turn LED3 on */
Error_Handler();
}
/****************************************************************************/
/* */
/* CRC computation of the last bytes stream */
/* */
/****************************************************************************/
/* The 7-bit long CRC of a 2-byte buffer is computed. The CRC calculator
is re-initialized with the default value that is 0x7F for a 7-bit CRC.
This is done with a call to HAL_CRC_Calculate() instead of
HAL_CRC_Accumulate(). */
uwCRCValue = HAL_CRC_Calculate(&CrcHandle, (uint32_t *)&CRC7_DATA8_TEST2, BUFFER_SIZE_2);
/* Compare the CRC value to the expected one */
if (uwCRCValue != uwExpectedCRCValue_4)
{
/* Wrong CRC value: Turn LED3 on */
Error_Handler();
}
else
{
/* Right CRC value: Turn LED1 on */
BSP_LED_On(LED1);
}
/* Infinite loop */
while (1)
{
}
}
The polynomial is 7 bits long, and I don't know the initial value, nor do I know whether to calculate only 7 bits or 8 bits. If only 7 bits are calculated, should I calculate the high 7 bits or the low 7 bits?
I wrote a C program, but the calculation results are wrong
uint8_t crc7_mpeg_2(uint8_t *data, uint16_t length)
{
uint8_t i;
uint32_t crc = 0x7f; // Initial value
while(length--)
{
crc ^= (*data++) << 0;
for (i = 0; i < 8; ++i)
{
if ( crc & 0x80 )
crc = (crc << 1) ^ 0x65;
else
crc <<= 1;
}
}
return (crc^0x00);
}
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