Marshal V-SG4K UART protocol CRC calculation

marshal_v_sg4k_3g_uart_crc.md

Protocol described in the official PDF mention CRC byte that complete each request and replay. But omit algorithm for it calculation.

After some researches, something sounds like true was found:

#include <iostream>
#include <cstdlib>

unsigned char checksum(const unsigned char *pcBlock, unsigned char len)
{
    uint32_t accu = 0;
    uint8_t crc = 0;
    
    while (len--)
        accu += *pcBlock++;
    
    accu ^= 0xFFFFFFFF;
    crc = (accu + 1) & 0xFF;
    
    return crc;
}

int main()
{
    const uint8_t buf0[] = {0xAA, 0x00, 0x00, 0x06, 0x00, 0x00, 0x00, 0x00, 0x61, 0x00, 0x00};
    const uint8_t buf1[] = {0xAB, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00, 0xFF, 0xFF, 0x61, 0x00, 0x00};
    std::cout << std::hex << (int)checksum(buf0, std::size(buf0)) << std::endl;
    std::cout << std::hex << (int)checksum(buf1, std::size(buf1)) << std::endl;
}

At least, it works as expected for the samples published in the protocol description.