3 Motion Control

The basic motion control logic should be timer interrupt driven. This logic is responsible to execute a motion profile based on displacement (distance), top velocity (speed), acceleration and deceleration. This module does not discuss this logic. Rather, this module assumes there is an interface to the basic motion control logic:

• int isDone(struct DiffSteer *p): This subroutine returns whether the motion of a differentially steered robot is done.
• void startMotion(struct DiffSteer *p,...): This subroutine requires a long list of parameters to start a differentially steered robot to move.
• void adjustD(struct Motion *p,...): This subroutine adjusts (adds or subrtracts) displacement to a motion control data structure. It also specifies the maximum velocity to be used. The acceleration and deceleration constants may be given, too.
• int getRemaining(struct Motion *p,...): This subroutine just returns the remaining (or distance) attribute of a motion control structure. It should be a subroutine because this access must be protected from interrupts. Read on for more information about protection from ISR.

Because the motion control logic is interrupt driven, there is not much that relates to threads. The only precaution is that any access of variables used in the ISR must be “protected”. This is because an interrupt can occur right in the middle of an access to a structure shared with the ISR. To ensure synchronzation with an ISR, interrupt should be disabled before the access, and restored after. For the AVR, the easiest way to do this is as follows: