= 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. It is an ''external'' peripheral.

The total number of channels must be defined by the configuration parameter NB_TIM_CHANNELS in the ''hard_config.h'' file.

The user timers  are allocated to applications by the GIET-VM in the boot phase, as defined in the mapping. The corresponding global index is stored in the context of the task.

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

The virtual base address of the associated segment is:   vbase = SEG_TIM_BASE + cluster_io << 32.

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.