There are several ways to read a Hall sensor. One way is to simply poll three I/O ports connected to the Hall sensor on a periodic basis, for example, in a timer interrupt handler.
You can also use one of the timers in input capture mode to read the sensor. Some of the STM32 timers have a way of XORing three inputs into a single signal that transitions on all rising and falling edges of the Hall inputs. These transitions also capture the value of the timer's counter in a register that you use to determine the rotational speed of the motor.
With regards to low motor speed, you will run into cases where the motor is turning so slowly that the timer overflows before a Hall transition occurs. You can mitigate this by increasing the timer prescaler to a larger value. Increasing the prescaler value will result in lower precision of the timing of the Hall transitions, so beware of increasing it more than necessary.
