Nanokernel +Timer

Creation

NTimer is +a basic relative timer provided by the nanokernel. It can generate either +a single interrupt or periodic interrupts. A timeout handler is called when +the timer expires, either from the timer ISR or from the nanokernel timer +thread. These timer objects can manipulated from any context. The timers are +driven from a periodic system tick interrupt, usually a 1ms period. The use +of NTimer is as follows:

Start

The +nanokernel timer can be used in either single mode or in periodic mode. Typically, +the timer is started with NTimer::OneShot() for a timeout +period and then is made periodic by calling NTimer::Again(). +The timeout value specified for the timer is in nanokernel ticks. The time +out callback function can be chosen to be called in either an ISR context +or a DFC context (running in the kernel's nanokernel timer thread, called DfcThread1).

TInt NTimer::OneShot(TInt aTime, TBool aDfc); +// If aDfc is TRUE then, the timeout function is called in a DFC context; +// if aDfc is FALSE, the timeout function is called in a ISR context. + +// Starts timer in zero-drift mode, to avoid delays in re-queuing +// the timer +TInt NTimer::Again(TInt aTime); + +// NTimer::OneShot() starts a nanokernel timer in one-shot mode with +// ISR callback. It queues the timer to expire in the specified number +// of nanokernel ticks. The actual wait time will be at least that +// much and may be up to one tick more. The expiry handler will be +// called in ISR context. +// +iRxPollTimer.OneShot(KRxTimeout);

Callback function

The +timeout callback function is called when a timer started with NTimer::OneShot() or NTimer::Again() expires. +A driver should implement the function to process the timeout event as appropriate +for the situation.

/** + Timer callback function. Called when the NTimer expires + typedef void(* NTimerFn)(TAny*); is the nanokernel timer callback + function. This is used for Rx timeout. + + @params aPtr + pointer refernce passed during timer initialization + */ +void DExUartPhysicalChannelH4::RxPollTimerCallback(TAny* aPtr) + { + ... // design specific + }

Cancellation

A +timer can be cancelled using NTimer::Cancel(). It removes +the timer object from the nanokernel timer queue. If the timer has already +expired, or is inactive, then it does nothing.

If a timer was queued +and a DFC callback was requested, then the expiry handler might run even after Cancel() has +been called. This occurs when the DfcThread1 is preempted +just before calling the expiry handler for this timer, and the preempting +thread/ISR/IDFC calls Cancel() on the timer.