Forward Backward Variable Single Pulse Timer

Forward Backward Variable Single Pulse Timer

Forward/Backward Variable (in short FBV) timers are capable to count forward to a preset value or backward to zero. The direction is determined by a Direction binary flag. It can be in one of the two states FBS_FORWARD and FBS_BACKWARD. The flag is controlled by the application - the application decides when the timer to count forward or backward.

While counting forward, when the timer's counter reaches the preset setting the timer's Expired flag is raised and the timer is stopped.

FBV timers have two variables that define steps for forward and for backward counting. This way it is possible to have different steps for the opposite directions.

While counting backward, when the timer's counter reaches zero it stays here (does not make integer overflow).

FB timers act as integrating circuits - they charge linearly a capacitor in FB_FORWARD mode and discharge linearly in FB_BACKWARD mode. The Setting value acts as a comparator's threshold. When the counter reaches the threshold the comparator toggles an Expired flag. FB timers can be used in algorithms implementing temperature protection.

An application may manipulate forward and backward steps depending on some external conditions. Par example if an FBV timer is used in temperature protection of a device, its forward step may be set bigger when the temperature is bigger. This way the timer will expire faster and will prevent the device from heat damage. Similarly, the backward step may simulate cooling.

Declaration.

Macro	Description
DEFINE_FBVSINGLE_PULSE_TIMER(tag,ttype)	Declare a FBV timer in .c file by decalring its variables. tag is the tag of the timer, and ttype is its type.
EXTERN_FBVSINGLE_PULSE_TIMER(tag,ttype)	Define external definitions in .h file. tag is the tag of the timer, and ttype is its type.

Variables.

Variable	Description
FBVSinglePulseTimerSetting(tag)	Setting of the timer of type ttype. It can be used as lvalue. This variable hold the value to which timer counters forward.
FBVSinglePulseTimerCounter(tag)	Counter of type ttype. It can be used as lvalue. Direct access to this variable is not recommended.
FBVSinglePulseTimerStepF(tag)	This variable accepts one of the two values FBS_BACKWARD and FBS_FORWARD. It can be used as lvalue. It determines the direction of the timer. Direct access to this variable is not recommended.
FBVSinglePulseTimerStepB(tag	Forward step of type ttype.
FBVSinglePulseTimerDirection(tag)	Backward step of type ttype.
FBVSinglePulseTimerFlag(tag)	When true, this flag indicates active, working timer. When false the flag indicates a stopped timer.
FBVSinglePulseTimerExpired(tag)	When true, the flag indicates that the time interval has expired. When false the flag indicates that the time interval is not expired or the timer is not started at all. It can be used as lvalue.

Manipulation macros.

Macro	Description
SetFBVSinglePulseTimer(tag,per,stepF,stepB,direction)	This macro activates a timer with tag tag. It sets the setting, the steps and the direction. The counter is set to zero. The macro disables the interrupts at the beginning and enables them at the end.
SetFBVSinglePulseTimerI(tag,per,stepF,stepB,direction)	This macro activates a timer with tag tag. It sets the setting, the steps and the direction. The counter is set to zero. The macro does not touch the interrupts and thus it is convenient to be used with previously disabled interrupts.
StopFBVSinglePulseTimer(tag)	This macro stops a timer with tag tag. It simply clears both FBVSinglePulseTimerFlag(tag) and FBVSinglePulseTimerExpired(tag). The macro disables the interrupts at the beginning and enables them at the end.
ResetFBVSinglePulseTimer(tag)	This macro stops a timer with tag tag. It simply clears both flags FBVSinglePulseTimerFlag(tag) and FBVSinglePulseTimerExpired(tag). The macro disables the interrupts at the beginning and enables them at the end of its execution.
ClearFBVSinglePulseTimer(tag)	This macro clears the variables of a timer with tag tag. The macro does not touch the interrupts and thus it is convenient to be used with previously disabled interrupts.
ClearFBVSinglePulseTimerExpired(tag)	This macro clears FBVSinglePulseTimerExpired(tag).
SetFBVSinglePulseTimerDirection(tag,d)	This macro changes the direction of counting.
ChangeFBVSinglePulseTimerSetting(tag,per)	This macro changes the setting FBVSinglePulseTimerSetting(tag). If FBVSinglePulseTimerCounter(tag) >= FBVSinglePulseTimerSetting(tag) the timer is stopped and FBVSinglePulseTimerExpired(tag) is risen.
SetFBVSinglePulseTimerStepF(tag,stepF)	This macro changes the forward step.
SetFBVSinglePulseTimerStepB(tag,stepB)	This macro changes the backward step.
TickFBVSinglePulseTimer(tag)	This macro executes increments or decrements FBSinglePulseTimerCounter(tag) depending on FBSinglePulseTimerDirection(tag). If counting forward, if after incrementing FBSinglePulseTimerCounter(tag) becomes equal ot greater than FBVSinglePulseTimerSetting(tag) the timer is stopped and FBVSinglePulseTimerExpired(tag) is risen. If counting backward, the counter is not decremented below zero.