microcontroller - MCP23017C++ erroneous values on read - Stack Overflow

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I am trying to read the GPIOB / GPIOA values through my program. This is a threaded program that gets messages over tcp/ip as a signal to change the pins.

    unsigned char gpioMon::subtractiveLookup(gpioMon::gpio_data gpio_data_in, unsigned char        registry, unsigned char value) {
        std::lock_guard<std::mutex> lock(i2c_mutex_);

        unsigned int handle = i2cOpen(gpio_data_in.i2c_bus,gpio_data_in.i2c_addr,0);

        std::this_thread::sleep_for(std::chrono::microseconds(50));
        int retcode = i2cReadByteData(handle,registry);//Read byte prior to writing it

        std::cout<<"Hello from gpioMon::subtractiveLookup()! Read value : "<<retcode<<"\n";
        unsigned char temp_holder = static_cast<unsigned char>(retcode) - value;

        std::this_thread::sleep_for(std::chrono::microseconds(50));

        std::cout<<"Hello from gpioMon::subtractiveLookup()! Writing value : "<<static_cast<int>(temp_holder)<<"\n";
        retcode = i2cWriteByteData(handle,registry,temp_holder);

        std::this_thread::sleep_for(std::chrono::microseconds(50));
        return retcode;
}

additiveLookup is the same function with an addition of "temp_holder" rather than a subtraction.

Here is the terminal output and where the odd things start to happen. I think it is due to a timing problem, but please let me know what you think it is...

    Hello from gpioMon::readInputs(). Message is dout1 on
    Hello from gpioPool::gpioRequest! Received mesage : dout1 on
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::additiveLookup()! Read value : 0
    Hello from gpioMon::additiveLookup()! Writing value : 1
    Received bytes : 9
    Hello from gpioMon::readInputs(). Message is dout1 off
    Hello from gpioPool::gpioRequest! Received mesage : dout1 off
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::subtractiveLookup()! Read value : 121
    Hello from gpioMon::subtractiveLookup()! Writing value : 120
    Received bytes : 8
    Hello from gpioMon::readInputs(). Message is dout1 on
    Hello from gpioPool::gpioRequest! Received mesage : dout1 on
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::additiveLookup()! Read value : 0
    Hello from gpioMon::additiveLookup()! Writing value : 1
    Received bytes : 9
    Hello from gpioMon::readInputs(). Message is dout1 off
    Hello from gpioPool::gpioRequest! Received mesage : dout1 off
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::subtractiveLookup()! Read value : 1
    Hello from gpioMon::subtractiveLookup()! Writing value : 0
    Received bytes : 8
    Hello from gpioMon::readInputs(). Message is dout1 on
    Hello from gpioPool::gpioRequest! Received mesage : dout1 on
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::additiveLookup()! Read value : 0
    Hello from gpioMon::additiveLookup()! Writing value : 1
    Received bytes : 9
    Hello from gpioMon::readInputs(). Message is dout1 off
    Hello from gpioPool::gpioRequest! Received mesage : dout1 off
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::subtractiveLookup()! Read value : 65
    Hello from gpioMon::subtractiveLookup()! Writing value : 64
    Received bytes : 8
    Hello from gpioMon::readInputs(). Message is dout1 on
    Hello from gpioPool::gpioRequest! Received mesage : dout1 on
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::additiveLookup()! Read value : 112
    Hello from gpioMon::additiveLookup()! Writing value : 113

If I run i2cget -y 1 0x27 0x13 after, it will show the real value. My fear is this program will actually write 113 to the registry and it will short out components.

What I am expecting to happen here is to read the registry and then add or subtract the current position from it. Example 0x00 + 0x01 --> GPIOB1 HI or 0x01 + 0x02 --> GPIOB0 HI / GPIOB1 HI .

I have tried adjusting the bus speed, adding in mutexes, adding in delays, trying file descriptors, trying pigpio methods. All seem to lead to the same outcome.

I think I am reading the documentation wrong and would appreciate some assistance with it.

I am trying to read the GPIOB / GPIOA values through my program. This is a threaded program that gets messages over tcp/ip as a signal to change the pins.

    unsigned char gpioMon::subtractiveLookup(gpioMon::gpio_data gpio_data_in, unsigned char        registry, unsigned char value) {
        std::lock_guard<std::mutex> lock(i2c_mutex_);

        unsigned int handle = i2cOpen(gpio_data_in.i2c_bus,gpio_data_in.i2c_addr,0);

        std::this_thread::sleep_for(std::chrono::microseconds(50));
        int retcode = i2cReadByteData(handle,registry);//Read byte prior to writing it

        std::cout<<"Hello from gpioMon::subtractiveLookup()! Read value : "<<retcode<<"\n";
        unsigned char temp_holder = static_cast<unsigned char>(retcode) - value;

        std::this_thread::sleep_for(std::chrono::microseconds(50));

        std::cout<<"Hello from gpioMon::subtractiveLookup()! Writing value : "<<static_cast<int>(temp_holder)<<"\n";
        retcode = i2cWriteByteData(handle,registry,temp_holder);

        std::this_thread::sleep_for(std::chrono::microseconds(50));
        return retcode;
}

additiveLookup is the same function with an addition of "temp_holder" rather than a subtraction.

Here is the terminal output and where the odd things start to happen. I think it is due to a timing problem, but please let me know what you think it is...

    Hello from gpioMon::readInputs(). Message is dout1 on
    Hello from gpioPool::gpioRequest! Received mesage : dout1 on
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::additiveLookup()! Read value : 0
    Hello from gpioMon::additiveLookup()! Writing value : 1
    Received bytes : 9
    Hello from gpioMon::readInputs(). Message is dout1 off
    Hello from gpioPool::gpioRequest! Received mesage : dout1 off
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::subtractiveLookup()! Read value : 121
    Hello from gpioMon::subtractiveLookup()! Writing value : 120
    Received bytes : 8
    Hello from gpioMon::readInputs(). Message is dout1 on
    Hello from gpioPool::gpioRequest! Received mesage : dout1 on
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::additiveLookup()! Read value : 0
    Hello from gpioMon::additiveLookup()! Writing value : 1
    Received bytes : 9
    Hello from gpioMon::readInputs(). Message is dout1 off
    Hello from gpioPool::gpioRequest! Received mesage : dout1 off
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::subtractiveLookup()! Read value : 1
    Hello from gpioMon::subtractiveLookup()! Writing value : 0
    Received bytes : 8
    Hello from gpioMon::readInputs(). Message is dout1 on
    Hello from gpioPool::gpioRequest! Received mesage : dout1 on
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::additiveLookup()! Read value : 0
    Hello from gpioMon::additiveLookup()! Writing value : 1
    Received bytes : 9
    Hello from gpioMon::readInputs(). Message is dout1 off
    Hello from gpioPool::gpioRequest! Received mesage : dout1 off
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::subtractiveLookup()! Read value : 65
    Hello from gpioMon::subtractiveLookup()! Writing value : 64
    Received bytes : 8
    Hello from gpioMon::readInputs(). Message is dout1 on
    Hello from gpioPool::gpioRequest! Received mesage : dout1 on
    Hello from gpioPool::gpioRequest! gpio_name : dout1
    Hello from gpioMon::additiveLookup()! Read value : 112
    Hello from gpioMon::additiveLookup()! Writing value : 113

If I run i2cget -y 1 0x27 0x13 after, it will show the real value. My fear is this program will actually write 113 to the registry and it will short out components.

What I am expecting to happen here is to read the registry and then add or subtract the current position from it. Example 0x00 + 0x01 --> GPIOB1 HI or 0x01 + 0x02 --> GPIOB0 HI / GPIOB1 HI .

I have tried adjusting the bus speed, adding in mutexes, adding in delays, trying file descriptors, trying pigpio methods. All seem to lead to the same outcome.

I think I am reading the documentation wrong and would appreciate some assistance with it.

• c++
• microcontroller

Share Improve this question Follow asked 15 hours ago emb3dd3demb3dd3d 111 bronze badge New contributor emb3dd3d is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct. 3

• what is "odd" about the output? – 463035818_is_not_an_ai Commented 15 hours ago
• 1 Snippets of code are of lesser value in a question except when discussing multithreaded code. In the latter case snippets are usually worthless. Strongly consider crafting a minimal reproducible example. – user4581301 Commented 15 hours ago
• @463035818_is_not_an_ai I was expecting it to say like 0x01 or 0x03... so on so forth instead of jumping to 0x73. I have since added close to the end, changed the i2c timing and it is much better performing now. – emb3dd3d Commented 13 hours ago

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1 Answer 1

Sorted by: Reset to default 0

I have since added close to the end, changed the i2c timing and it is much better performing now

open i2c
write addr, registry
read addr,registry
add/subtract char values

wait 50 milliseconds
write addr,registry,new_value

Thanks for the replies

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