sof_packet() is generating invalid CRC5 values

Based on the paper at https://www.michael-joost.de/crc5check.pdf I came up with the following program:

#include <stdio.h>
#include <stdint.h>

const uint8_t crc5Table4[] =
        {
            0x00, 0x0E, 0x1C, 0x12, 0x11, 0x1F, 0x0D, 0x03,
            0x0B, 0x05, 0x17, 0x19, 0x1A, 0x14, 0x06, 0x08};
const uint8_t crc5Table0[] =
        {
            0x00, 0x16, 0x05, 0x13, 0x0A, 0x1C, 0x0F, 0x19,
            0x14, 0x02, 0x11, 0x07, 0x1E, 0x08, 0x1B, 0x0D};
//---------------
int crc5Check(const uint8_t *data)
//---------------
{
    uint8_t b = data[0] ^ 0x1F;
    uint8_t crc = crc5Table4[b & 0x0F] ^ crc5Table0[(b >> 4) & 0x0F];
    b = data[1] ^ crc;
    return (crc5Table4[b & 0x0F] ^ crc5Table0[(b >> 4) & 0x0F]) == 0x06;
}
//  crc5Check

int do_check(uint16_t pkt) {
    uint8_t data[2] = {
        pkt >> 8,
        pkt
    };
    return crc5Check(data);
}

#define ARRAY_SIZE(x) (sizeof(x) / sizeof(*x))
int main(int argc, char **argv)
{
    uint32_t check_bytes[] = {
        0x1ab5,
        0x19f5,
        0x481b,
        0x4d85,
    };
    unsigned int i;

    for (i = 0; i < ARRAY_SIZE(check_bytes); i++)
        printf("CRC5 check: 0x%04x %d\n", check_bytes[i], do_check(check_bytes[i]));
    return 0;
}

Values for check_bytes[] can be generated in Python:

>>> from valentyusb.usbcore.utils.packet import sof_packet
>>> hex(eval("0b" + sof_packet(1429))-0xa50000)
'0x4d85'
>>>

The values 0x1ab5 and 0x19f5 were seen in wire dumps. The values 0x481b and 0x4d85 are taken from the examples. The values generated by valentyusb are incorrect:

$ ./test
CRC5 check: 0x1ab5 1
CRC5 check: 0x19f5 1
CRC5 check: 0x481b 0
CRC5 check: 0x4d85 0
$

Leaving this here, because it could be useful. This takes packets and extracts the CRC and data. It then attempts to recreate the packet based on the CRC that it found.

#include <stdio.h>
#include <stdint.h>

const uint8_t crc5Table4[] =
        {
            0x00, 0x0E, 0x1C, 0x12, 0x11, 0x1F, 0x0D, 0x03,
            0x0B, 0x05, 0x17, 0x19, 0x1A, 0x14, 0x06, 0x08};
const uint8_t crc5Table0[] =
        {
            0x00, 0x16, 0x05, 0x13, 0x0A, 0x1C, 0x0F, 0x19,
            0x14, 0x02, 0x11, 0x07, 0x1E, 0x08, 0x1B, 0x0D};
//---------------
int crc5Check(const uint8_t *data)
//---------------
{
    uint8_t b = data[0] ^ 0x1F;
    uint8_t crc = crc5Table4[b & 0x0F] ^ crc5Table0[(b >> 4) & 0x0F];
    b = data[1] ^ crc;
    return (crc5Table4[b & 0x0F] ^ crc5Table0[(b >> 4) & 0x0F]) == 0x06;
}
//  crc5Check

int do_check(uint16_t pkt) {
    uint8_t data[2] = {
        pkt >> 8,
        pkt,
    };
    return crc5Check(data);
}

#define INT_SIZE 32
unsigned CRC5(unsigned dwInput, int iBitcnt)
{
    const uint32_t poly5 = (0x05 << (INT_SIZE-5));
    uint32_t crc5  = (0x1f << (INT_SIZE-5));
    uint32_t udata = (dwInput << (INT_SIZE-iBitcnt));

    if ( (iBitcnt<1) || (iBitcnt>INT_SIZE) )    // Validate iBitcnt
        return 0xffffffff;

    while (iBitcnt--)
    {
        if ( (udata ^ crc5) & (0x1<<(INT_SIZE-1)) ) // bit4 != bit4?
        {
            crc5 <<= 1;
            crc5 ^= poly5;
        }
        else
            crc5 <<= 1;

        udata <<= 1;
    }

    // Shift back into position
    crc5 >>= (INT_SIZE-5);

    // Invert contents to generate crc field
    crc5 ^= 0x1f;

    return crc5;
} //CRC5()

static uint32_t reverse_sof(uint32_t data) {
    int i;
    uint32_t data_flipped = 0;
    for (i = 0; i < 11; i++)
        if (data & (1 << i))
            data_flipped |= 1 << (10 - i);

    return data_flipped;
}

static uint8_t reverse_byte(uint8_t data) {
    int i;
    uint8_t data_flipped = 0;
    for (i = 0; i < 8; i++)
        if (data & (1 << i))
            data_flipped |= 1 << (7 - i);

    return data_flipped;
}

static uint8_t reverse_crc5(uint8_t data) {
    int i;
    uint8_t data_flipped = 0;
    for (i = 0; i < 5; i++)
        if (data & (1 << i))
            data_flipped |= 1 << (4 - i);

    return data_flipped;
}

static uint16_t make_token(uint16_t data) {
    uint16_t val = 0;

    data = reverse_sof(data);
    val = data << 5;
    val |= CRC5(data, 11);

    return (reverse_byte(val >> 8) << 8) | reverse_byte(val);
}

int do_crc5(uint16_t pkt) {
    uint8_t pkt_flipped[2] = {
        reverse_byte(pkt >> 8),
        reverse_byte(pkt),
    };
    uint32_t data = (pkt_flipped[1] >> 5) | (pkt_flipped[0] << 3);
    uint32_t data_flipped;
    uint8_t crc;
    uint8_t found_crc = (pkt >> 3) & 0x1f;

    data_flipped = reverse_sof(data);

    crc = CRC5(data, 11);
    crc = reverse_crc5(crc);

    uint16_t reconstructed = make_token(data_flipped);

    printf("Packet: 0x%04x  FCRC: %02x  Data: 0x%04x  Flipped: 0x%04x  CRC5: 0x%02x  Pass? %d  Reconstructed: 0x%04x\n",
        pkt, found_crc, data, data_flipped, crc, do_check(pkt),
        reconstructed
        );

    return crc;
}

#define ARRAY_SIZE(x) (sizeof(x) / sizeof(*x))
int main(int argc, char **argv)
{
    uint32_t check_bytes[] = {
        0x0225,
        0x0165,
        0x009d,
        0x102f,
    };

    unsigned int i;

    for (i = 0; i < ARRAY_SIZE(check_bytes); i++)
        do_crc5(check_bytes[i]);

    return 0;
}

mithro / valentyusb

sof_packet() is generating invalid CRC5 values #27