GIET-VM / BDV Driver

The tim_driver.c​ and 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 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.