c-如何使用stm32l1 CRC单元计算1字节的CRC

Question

我正在尝试使用stm32l152的CRC计算单元来计算单字节数据输入的CRC。
CRC单元只接受32位输入。我本来可以让它计算32位数据输入的CRC，但现在我很难让它为字节数据输入工作。

我的测试输入数据是0x20，我希望输出0xD62B0954
CRC参数：polynom0x04C11DB7，初始值：0xFFFFFFFF

我怎么能解决这个问题，我已经没有主意了？

32位数据的示例代码：

CRC->DR = u32Input`  
u32Crc = CRC->DR;

我还发现了这个代码片段，用于按字节计算CRC，但输出不同。

static uint32_t crc32_step(uint32_t crc, uint8_t data)
{
crc = ~crc ^ data;
CRC->DR = (~CRC->DR) ^ __RBIT(~(crc << 24));
return (crc >> 8) ^ ~__RBIT(CRC->DR);
}

我使用上面的代码获得以下输出，并提供了0xFFFFFFFF:0xC491DF37的crc

我真的不明白crc32_step函数的作用，但我甚至不确定这是否是正确的方向。如果有任何提示或想法，我将不胜感激。

Answer 1

正在计算的CRC似乎是CRC-32/MPEG2。这里有一些简单的C代码来计算它：

#include <stddef.h>
#include <stdint.h>
uint32_t crc32mpeg2(uint32_t crc, void const *mem, size_t len) {
unsigned char const *data = mem;
if (data == NULL)
return 0xffffffff;
while (len--) {
crc ^= (uint32_t)(*data++) << 24;
for (unsigned k = 0; k < 8; k++)
crc = crc & 0x80000000 ? (crc << 1) ^ 0x04c11db7 : crc << 1;
}
return crc;
}

用NULL为mem调用该例程以获得初始CRC值。所以它会这样使用：

#include <stdio.h>
int main(void) {
unsigned char data[1] = { 0x20 };
uint32_t crc = crc32mpeg2(0, NULL, 0);
crc = crc32mpeg2(crc, data, 1);
printf("%08xn", crc);
return 0;
}

输出为：

d62b0954

Answer 2

在软件中计算crc最有效的方法是使用一个表，一次计算八位。下表允许您计算这些：

#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
static uint32_t crc32mpeg2_table[] = {
0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc, 0x17c56b6b, 0x1a864db2, 0x1e475005,
0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61, 0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd,
0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9, 0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75,
0x6a1936c8, 0x6ed82b7f, 0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3, 0x709f7b7a, 0x745e66cd,
0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039, 0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5,
0xbe2b5b58, 0xbaea46ef, 0xb7a96036, 0xb3687d81, 0xad2f2d84, 0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d,
0xd4326d90, 0xd0f37027, 0xddb056fe, 0xd9714b49, 0xc7361b4c, 0xc3f706fb, 0xceb42022, 0xca753d95,
0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1, 0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d,
0x34867077, 0x30476dc0, 0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c, 0x2e003dc5, 0x2ac12072,
0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16, 0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca,
0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde, 0x6b93dddb, 0x6f52c06c, 0x6211e6b5, 0x66d0fb02,
0x5e9f46bf, 0x5a5e5b08, 0x571d7dd1, 0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e, 0xbfa1b04b, 0xbb60adfc, 0xb6238b25, 0xb2e29692,
0x8aad2b2f, 0x8e6c3698, 0x832f1041, 0x87ee0df6, 0x99a95df3, 0x9d684044, 0x902b669d, 0x94ea7b2a,
0xe0b41de7, 0xe4750050, 0xe9362689, 0xedf73b3e, 0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683, 0xd1799b34, 0xdc3abded, 0xd8fba05a,
0x690ce0ee, 0x6dcdfd59, 0x608edb80, 0x644fc637, 0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb,
0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f, 0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53,
0x251d3b9e, 0x21dc2629, 0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5, 0x3f9b762c, 0x3b5a6b9b,
0x0315d626, 0x07d4cb91, 0x0a97ed48, 0x0e56f0ff, 0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623,
0xf12f560e, 0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2, 0xe6ea3d65, 0xeba91bbc, 0xef68060b,
0xd727bbb6, 0xd3e6a601, 0xdea580d8, 0xda649d6f, 0xc423cd6a, 0xc0e2d0dd, 0xcda1f604, 0xc960ebb3,
0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7, 0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b,
0x9b3660c6, 0x9ff77d71, 0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad, 0x81b02d74, 0x857130c3,
0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640, 0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c,
0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8, 0x68860bfd, 0x6c47164a, 0x61043093, 0x65c52d24,
0x119b4be9, 0x155a565e, 0x18197087, 0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b, 0x0fdc1bec,
0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088, 0x2497d08d, 0x2056cd3a, 0x2d15ebe3, 0x29d4f654,
0xc5a92679, 0xc1683bce, 0xcc2b1d17, 0xc8ea00a0, 0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb, 0xdbee767c,
0xe3a1cbc1, 0xe760d676, 0xea23f0af, 0xeee2ed18, 0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5, 0x9e7d9662, 0x933eb0bb, 0x97ffad0c,
0xafb010b1, 0xab710d06, 0xa6322bdf, 0xa2f33668, 0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4,
};
uint32_t crc32mpeg2(uint32_t state, uint8_t *buff, size_t buff_sz)
{
while (buff_sz-- > 0) {
int index = (state >> 24) ^ *buff++;
state <<= 8;
state ^= crc32mpeg2_table[index];
}
return state;
}
/* this main() function to demonstrate that the crc 
* applied to a string with a single space character works */
int main()
{
uint8_t buff[] = { 0x20 };
uint32_t crc = crc32mpeg2(0xffffffff, buff, sizeof buff);
printf("0x%08xn", crc);
}

正如您所看到的，在将其应用于输入缓冲区之后，结果是预期值：

$ ./crcmpg3 
0xd62b0954
$ _

要生成该表，您只需运行Mark Adler(@MarkAdler(在其响应中提出的算法，即可获得完整的可能输入字节集(从0x00到0xff(，如下所示：

#include <stddef.h>
#include <stdio.h>
#include <stdint.h>
/* this is the function provided by Mark in his response */
uint32_t crc32mpeg2(uint32_t crc, void const *mem, size_t len) {
unsigned char const *data = mem;
if (data == NULL)
return 0xffffffff;
while (len--) {
crc ^= (uint32_t)(*data++) << 24;
for (unsigned k = 0; k < 8; k++)
crc = crc & 0x80000000 ? (crc << 1) ^ 0x04c11db7 : crc << 1;
}
return crc;
}
int main()
{
int i;
char *sep = "uint32_t crc32mpeg2_table[] = {nt";
for (i = 0; i < 256; i++) {
status = crc32mpeg2(i & 0xff, &ch, sizeof ch);
printf("%s0x%08x", sep, status);
sep = i % 8 == 7 ? ",nt" : ", ";
}
printf("n};n");
}

它将生成上表。一旦你有了表，你只需要使用这个函数(更快，因为你每次迭代操作一个完整的字节(就可以得到结果：

uint32_t crc32mpeg2(uint32_t state, uint8_t *buff, size_t buff_sz)
{
while (buff_sz-- > 0) {
int index = (state >> 24) ^ *buff++;
state <<= 8;
state ^= crc32mpeg2_table[index];
}
return state;
}

该函数的正确用法是通过传递旧状态(即处理完的最后一个字节的CRC(来调用它，以获得新状态(处理完一组新字节后的新CRC(。该状态的第一个值必须初始化为0xffffffff，因此要计算"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua."的CRC，可以使用以下main：

#include <string.h>
#include <stddef.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
int main()
{
/* first piece */
char *s = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, ";
uint32_t crc = crc32mpeg2(0xffffffff, s, strlen(s)); /* intialize with 0xffffffff */
printf("CRC("%s", s);
/* second piece */
s = "sed do eiusmod tempor incididunt ut labore et dolore ";
crc = crc32mpeg2(crc, s, strlen(s));
printf("%s", s);
/* third piece */
s = "magna aliqua.";
crc = crc32mpeg2(crc, s, strlen(s));
printf("%s") => ", s);
/* print crc of the whole string */
printf("0x%08xn", crc);
}

应该输出：

$ crcmpg3.c
CRC("Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.") => 0x81e9201f
$ _