DRV8412/8432: how to control rotation direction and rotation speed?

Hi all,

I'm a little confused by datasheet and some example code.

for motor control, I want to know,

1. under mode 1 (or mode 2), does one pwm control left bridge while the other pwm control right bridge? do i need do some special to avoid shoot-through? and how is direction controlled? and how is speed controlled?

2. under mode 4, does the motor rotate in one direction with duty cycle greater than 50%, and in the reverse direction with duty cycle less than 50%? and more deviation from 50%, greater speed?

3. when is mode 3 recommended? 

Any reply is greatly appreciated.