= GIET-VM / XCU Driver = 

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

The ''vci_xcu'' component is an extended interrupt controller, available in the SoCLib components library, and supporting three types of interrupts:
 * '''HWI''' : Hardware Interrupts (from hardware peripherals)
 * '''PTI''' : Programmable Timer Interrupts (contained in the XCU component)
 * '''WTI''' : Write Trigered Interrupts (from software, or from a PIC controller) 

The GIET-VM uses three 32 entries interrupt vectors (one interrupt vector for each interrupt type).

The CXU component is a replicated peripheral: it must exist one XCU per cluster, and each one can contain several channels:
The number of XICU channels is equal to NB_PROCS_MAX, because there is one private XCU channel per processor in a cluster.

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

The SEG_XCU_BASE and PERI_CLUSTER_INCREMENT values must be defined in the hard_config.h file.

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

 === void '''_xcu_set_mask'''( unsigned int cluster_xy,  unsigned int channel,    unsigned int mask,   unsigned int irq_type ) ===
This function set the mask register for the IRQ type defined by "irq_type",
and for the channel identified by the "cluster_xy" and "channel" arguments.
All '1' bits are set / all '0' bits are not modified.

 === void '''_xcu_get_index'''( unsigned int   cluster_xy,   unsigned int   channel,   unsigned int * index,  unsigned int * irq_type ) ===
This function returns the index and the type of the highest priority active interrupt:
1. active PTI (Timer Interrupt),
2. active HWI (Hardware Interrupt),
3. active WTI (Software Interrupt)

 === void '''_xcu_send_wti'''( unsigned int cluster_xy,   unsigned int wti_index,   unsigned int wdata ) ===
This function writes the ''wdata'' value in the mailbox defined by the ''cluster_xy'' and ''wti_inde'' arguments.

 === void '''_xcu_get_wti_value'''( unsigned int   cluster_xy,   unsigned int   wti_index,   unsigned int * value ) ===
This function returns the value contained in a WTI mailbox defined by the ''cluster_xy'' and ''wti_index'' arguments. This value is written in the ''value'' argument, and the corresponding WTI is acknowledged.

 === void '''_xcu_get_wti_address'''( unsigned int   wti_index,  unsigned int * address ) ===
This function returns the physical address of the WTI mailbox in cluster [0][0], defined by the ''wti_index'' argument, in the ''address'' argument.
It is used by the GIET to configurate the IOPIC component. There is no access to a specific XCU component in a specific cluster.

 === void '''_xcu_timer_start'''( unsigned int cluster_xy,   unsigned int pti_index,  unsigned int period ) === 
This function activates a timer contained in XCU by writing in the proper register the period value.

 === void '''_xcu_timer_stop'''( unsigned int cluster_xy,   unsigned int pti_index ) == 
This function desactivates a timer in XCU component by writing in the proper register.

 === unsigned int '''_xcu_timer_reset_irq'''( unsigned int cluster_xy,   unsigned int pti_index ) ===
This function acknowlegge a timer interrupt in XCU component by reading in the proper XCU register.
It is used by both the isr_switch() for a system timer,  or by the _isr_timer() for an user timer.

 === void '''_xcu_timer_reset_cpt'''( unsigned int cluster_xy,  unsigned int pti_index ) ===
This function resets a timer counter. To do so, it read in the TIMER_PERIOD register, and rewrite the same value in the same register,
what causes the count to restart. This function is called during a context switch (user or preemptive).