How to calulate CRC of 1 byte using stm32l1 CRC unit

I'm trying to calculate the CRC of a one byte data input using the CRC calculation unit of the stm32l152.
The CRC unit accepts only 32Bit inputs. I was able to get it calculate the CRC for a 32Bit data input, but now I'm struggling to get it to work for a byte data input.

My test input data is 0x20 and I expect as output 0xD62B0954
CRC parameter: polynom 0x04C11DB7, init-val: 0xFFFFFFFF

How can I solve this, I'm running out of ideas?

Sample code for the 32 bit data:

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

I've also found this code snippet, to calculate the CRC byte-wise, but the output is different.

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);
}

I get the following output using the code above with a provided crc of 0xFFFFFFFF: 0xC491DF37

I don't really understand what the crc32_step function does, but I'm not even sure if this is the right direction to go. I would greatly appreciate any hints or ideas.

Solution

The CRC being calculated appears to be a CRC-32/MPEG2. Here is some simple code in C to calculate it:

#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;
}

The routine is called with NULL for mem to get the initial CRC value. So it would be used like this:

#include <stdio.h>

int main(void) {
    unsigned char data[1] = { 0x20 };
    uint32_t crc = crc32mpeg2(0, NULL, 0);
    crc = crc32mpeg2(crc, data, 1);
    printf("%08x\n", crc);
    return 0;
}

The output is:

d62b0954