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# Library prosa.model.processor.spin

Require Export prosa.behavior.all.
In the following, we define a processor state that includes the possibility of spinning, where spinning jobs do not progress (= don't get any service).
NB: For now, the definition serves only to document how this can be done; it is not actually used anywhere in the library.
Section State.
Consider any type of jobs.
Variable Job : JobType.
We define the state of a processor at a given time to be one of three possible cases: either a specific job is scheduled and makes progress Progress j, a specific job is scheduled but makes not useful progress Spin j, or the processor is idle Idle.
Inductive processor_state :=
Idle
| Spin (j : Job)
| Progress (j : Job).
Next, we define the semantics of the processor state with spinning.
Section Service.
Let j denote any job.
Variable j : Job.
It is scheduled in a given state s iff the state is not idle and j is the job mentioned in the state.
Definition spin_scheduled_on (s : processor_state) (_ : unit) : bool :=
match s with
| Idle ⇒ false
| Spin j' ⇒ j' == j
| Progress j' ⇒ j' == j
end.
If the processor is idle, we assume that the supply equals 1, indicating that the processor is ready to perform work. If the processor is in the state Spin j, then the job does not make any progress, so effectively the supply is equal to 0. Finally, the processor being in the state Progress j indicates that the processor carries out 1 unit of useful work.
Definition spin_supply_on (s : processor_state) (_ : unit) : work :=
match s with
| Idle ⇒ 1
| Spin j ⇒ 0
| Progress j ⇒ 1
end.
A job j receives service only if the given state s is Progress j.
Definition spin_service_on (s : processor_state) (_ : unit) : work :=
match s with
| Idle ⇒ 0
| Spin j' ⇒ 0
| Progress j' ⇒ j' == j
end.
End Service.
Finally, we connect the above definitions with the generic Prosa interface for abstract processor states.
Program Definition pstate_instance : ProcessorState Job :=
{|
State := processor_state;
scheduled_on := spin_scheduled_on;
supply_on := spin_supply_on;
service_on := spin_service_on
|}.
Next Obligation. by move ⇒ j [] // s [] /=; case: eqP. Qed.
Next Obligation. by move ⇒ j [] // s [] /=; case: eqP. Qed.
End State.