timer Module

Files:

Interface:

Function: InitPorts
Arguments: None.
Returns: None.
Description:Initializes the AD Ports.

Function: InitTimer
Arguments: None.
Returns: None.
Description:Initializes the Absolute Timer

Function: StartTimer
Arguments: Character representing the timer number and unsigned long representing timer duration in ms
Returns: CornerBeacons_t structure containing a character representing the side, the duty of the opponents side, and the duty of the friendly side.
Description:Returns the CornerBeacons structure for the current side.
Timer 1 is Left Encoder Stall Test
Timer 2 is Right Encoder Stall Test
Timer 3 is ControlLaw Update

Function: IsTimerExpired
Arguments: Character representing the timer number
Returns: Character representing TRUE when timer has expired.
Description:Checks if requested timer has expired.

Function: GetAbsoluteTime
Arguments: None
Returns: Unsigned long representing the absolute time in ticks
Description:retrieves the detected duty of the referenced beacon.

Pseudo-Code:

 
void InitPorts(void)
   Initialize ports to "IIIAAAAA" configuration
  
void InitTimer(void)
   Set up Timer 0 which is for the encoders
       Turn the timer system on
       Set timer prescale to divide by 128
           Enable interrupts for IC4, IC5, OC6
       Capture rising edges on 4,5,7
       Set timer 0-6 as output compare
       Schedule the first OC6 event
       Clear IC4, IC5, OC6, IC7 flag
       Clear overflow flag
       Turn on overflow interrupts
   
   Second, Timer 1 which is for the beacons, and the absolute timer 
       Turn the timer system on
	  Set timer prescale to divide by 128
       Enable interrupts for IC4-7               
   
   Set up Timers for capturing beacon edges, and clear flags
       Capture all edges on pin 4
       Capture all edges on pin 5 
       Capture all edges on pin
       Capture all edges on pin 7
       Clear IC4-IC7 flags
       Clear overflow flag
       Turn on overflow interrupts

   Initialize absolute timer 
   Set all timers to not started 
   Start Flag Captured Timer
	  

void StartTimer(char TimerNum, unsigned long ms_duration)
   Calculate ms value in clock ticks. May be truncated
   Calculate end time and store in timer

    
char IsTimerExpired(char TimerNum)
   If Timer has started and the value of the timer is less than the absolute time
       Reset the Timer Expired flag 
       Return TRUE
   Else
       Return FALSE
    
unsigned long GetAbsoluteTime(void)
   Disable overflow interrupts
   Set the Absolute Time to the current tick count in the timer register
   Enable overflow interrupts
   Return the Absolute Time in ticks
        
short GetBeaconLevel(char BeaconPin)
   Return the AD value on the requested pin
    
unsigned char Orientation(void)
    If Front two beacons detect 70% duty
        Return "Facing 70" value
    Else If Front two beacons detect 30% duty
        Return "Facing 30" value
    Else If Left beacon detects 70% duty and Right beacon detects 30% duty
        Return 70LEFT_30RIGHT
    Else if Left beacon detects 30% duty and Right beacon detects 70% duty
        Return Return 30LEFT_70RIGHT
    Else
        Return NO_SIGNAL_DETECTED


Interrupts:
       
void interrupt _Vec_tim1ovf Tim1OverflowInterrupt(void)
Increments the overflow counter for timer 1, for absolute timing purposes
    Increment Overflow Counter
    Clear Overflow interrup flag