'global' i2c mutex across all i2c buses causing contention

Mbed OS
10

Hello Wayne,

Nice analyses! And you are right. There is a flaw in the acquire function.

I think the intent of the I2C class designer was to allow connecting I2C slaves using various clock frequencies to the same I2C bus (have a look at this bug). One solution could be to check the associated peripheral (I2C controller) in the aquire member function.

For example as follows:

void I2C::aquire()
{
    struct i2c_s *_owner_s = I2C_S(_owner);
    struct i2c_s *this_s = I2C_S(this); 

    lock();
    if (_owner != this) {
        if  (_owner_s->i2c == this_s->i2c) {
            i2c_frequency(&_i2c, _hz);
        }
        _owner = this;
    }
    unlock();
}

NOTE: The same flaw is present in the SPI class.