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c++arduinochecksumesp32

How to Calculate Checksum in Arduino/C++?

I'm developing an ESP32(Arduino) interface to communicate to a Fingerprint Device. But I have no idea about the checksum. I found documentation for the Fingerprint device as below.

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For example, some of the data packets are followed:

enter image description here

Here, the checksum of the corresponding command packets are. 06 01, F7 02, FA 02, F8 03, FA 02, F9 03

My question is How can I calculate the checksum for a new data packet in Arduino/ C++, for example:

the data packet is:

AA 55 04 01 04 00 00 00 F4 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 ?? ??

What will be the Process?

Thank you!

Solution

  • The specification is very poorly written and vague but just adding up all the bytes in the message and taking the lower 2 bytes of the result seems to produce the right checksum:

    #include <vector>
#include <cstdint>
#include <iostream>
#include <iomanip>

int main()
{
    std::vector<uint8_t> data{ 0x55, 0xaa, 0x03, 0x01, 0x02, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
    int sum = 0;
    for (auto x : data)
    {
        sum += x;
    }
    uint8_t sum1 = static_cast<uint8_t>(sum & 0xFF);
    uint8_t sum2 = static_cast<uint8_t>((sum >> 8) & 0xFF);
    std::cout << std::setfill('0') << std::hex <<
        std::setw(2) << static_cast<int>(sum1) << " " <<
        std::setw(2) << static_cast<int>(sum2) << "\n";
}