= GIET-VM / BDV Driver = 

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The [source:soft/giet_vm/giet_drivers/tim_driver.c tim_driver.c] and [source:soft/giet_vm/giet_drivers/tim_driver.h tim_driver.h] files define the TIM driver. 

The ''vci_multi_timer'' component is a multi-channels timer controller. 

For the GIET, it is an ''internal'' peripheral, replicated in each cluster.

The SEG_TIM_BASE address must be defined in the hard_config.h file.

There is two types of timers: 
 * '''kernel timers''' : one per processor, used for context switch. The local_id is in [0, NB_PROCS_MAX-1].
 * '''user timers''' : requested by the task in the mapping_info data structure. The local_id is in [NB_PROCS_MAX, NB_PROCS_MAX + NB_TIM_CHANNELS -1].

The global timer index is cluster_xy * (NB_PROCS_MAX + NB_TIM_CHANNELS) + local_id

The virtual base address of the associated segment is:   vbase = SEG_TIM_BASE + cluster_xy * PERI_CLUSTER_INCREMENT

The SEG_TIM_BASE, PERI_CLUSTER_INCREMENT, NB_PROCS_MAX and NB_TIM_CHANNELS values must be defined in hard_config.h file.

The addressable registers map is defined [source:soft/giet_vm/giet_drivers/tim_driver.h here].




 === int '''_timer_start'''( unsigned int cluster_xy,  unsigned int local_id,  unsigned int period ) === 
This function activates a timer in the vci_timer component by writing in the proper register the period value.
It can be used by both the kernel to initialise a "system" timer, or by a task (through a system call) to configure an "user" timer.
Return 0 in case of success.
Return -1 if timer index too large.

 === int '''_timer_stop'''( unsigned int cluster_xy,  unsigned int local_id ) ===
This function desactivates a timer in the vci_timer component by writing in the proper register.
Return 0 in case of success.
Return -1 if timer index too large.

 === int '''_timer_reset_irq'''( unsigned int cluster_xy,  unsigned int local_id ) ===
This function acknowlegge a timer interrupt in the vci_timer  component by writing in the proper register.
It can be used by both the isr_switch() for a "system" timer, or by the _isr_timer() for an "user" timer.
Return 0 in case of success.
Return -1 if timer index too large.

 === int '''_timer_reset_cpt'''( unsigned int cluster_xy,   unsigned int local_id) ===
This function resets the timer counter. To do so, we re-write the period in the proper register, what causes the count to restart.
This function is called during a context switch (user or preemptive).
Return 0 in case of success.
Return -1 if timer index too large.

 === void '''_timer_isr'''( unsigned int irq_type,  unsigned int irq_id,  unsigned int channel ) ===
This Interrupt Service Routine handles the IRQs generated by the "user" timers.
The IRQs generated by the "system" timers should be handled by _isr_switch().
It can be a HWI or a PTI. The channel argument is the timer local index.
The ISR acknowledges the IRQ, registers the event in the proper entry
of the _user_timer_event[] array, and a log message is displayed on TTY0.