source: soft/giet_vm/giet_kernel/ctx_handler.c @ 423

//////////////////////////////////////////////////////////////////////////////////
// File     : ctx_handler.c
// Date     : 01/04/2012
// Authors  : alain greiner & joel porquet
// Copyright (c) UPMC-LIP6
//////////////////////////////////////////////////////////////////////////////////

#include <giet_config.h>
#include <tim_driver.h>
#include <xcu_driver.h>
#include <tty_driver.h>
#include <utils.h>
#include <ctx_handler.h>
#include <mapping_info.h>
#include <sys_handler.h>

extern void _task_switch(unsigned int *, unsigned int *);

/////////////////////////////////////////////////////////////////////////////////
// This function performs a context switch between the running task
// and  another task, using a round-robin sheduling policy between all
// tasks allocated to a given processor (static allocation).
// It selects the next runable task to resume execution. 
// If the only runable task is the current task, return without context switch.
// If there is no runable task, the scheduler switch to the default "idle" task.
/////////////////////////////////////////////////////////////////////////////////
// Implementation note
// The return address contained in $31 is saved in the current task context
// (in the ctx[31] slot), and the function actually returns to the address
// contained in the ctx[31] slot of the next task context.
/////////////////////////////////////////////////////////////////////////////////
void _ctx_switch() 
{
    unsigned int gpid       = _get_procid();
    unsigned int cluster_xy = gpid / NB_PROCS_MAX;
    unsigned int lpid       = gpid % NB_PROCS_MAX;

    // get scheduler address
    static_scheduler_t* psched = (static_scheduler_t*)_get_sched();

    // get number of tasks allocated to scheduler
    unsigned int tasks = psched->tasks;

    // get current task index
    unsigned int curr_task_id = psched->current;

    // select the next task using a round-robin policy
    unsigned int next_task_id;
    unsigned int tid;
    unsigned int found = 0;

    for (tid = curr_task_id + 1; tid < curr_task_id + 1 + tasks; tid++) 
    {
        next_task_id = tid % tasks;
        // test if the task is runable
        if ( psched->context[next_task_id][CTX_RUN_ID] ) 
        {
            found = 1;
            break;
        }
    }

    // launch "idle" task if no runable task
    if (found == 0) 
    {
        next_task_id = IDLE_TASK_INDEX;
    }

#if GIET_DEBUG_SWITCH
unsigned int x = cluster_xy >> Y_WIDTH;
unsigned int y = cluster_xy & ((1<<Y_WIDTH)-1);

_printf("\n[TASK SWITCH] (%d) -> (%d) on processor[%d,%d,%d] at cycle %d\n",
        curr_task_id, next_task_id, x, y , lpid, _get_proctime() );
#endif

    if (curr_task_id != next_task_id)  // actual task switch required
    {
        unsigned int* curr_ctx_vaddr = &(psched->context[curr_task_id][0]);
        unsigned int* next_ctx_vaddr = &(psched->context[next_task_id][0]);

        // reset timer counter. 
        // In all clusters, the first NB_PROCS_MAX
        // timers are system timers (TICK)

#if USE_XCU
        _xcu_timer_reset_cpt( cluster_xy, lpid );
#else
        _timer_reset_cpt( cluster_xy, lpid); 
#endif

        // set current task index 
        psched->current = next_task_id;

        // makes context switch
        _task_switch(curr_ctx_vaddr, next_ctx_vaddr);
    }
} //end _ctx_switch()

/////////////////////////////////////////////////////////////////////////////////////
// This function is executed as the"idle" task when no other task can be executed 
/////////////////////////////////////////////////////////////////////////////////////
void _idle_task() 
{
    unsigned int gpid       = _get_procid();
    unsigned int cluster_xy = gpid / NB_PROCS_MAX;
    unsigned int lpid       = gpid % NB_PROCS_MAX;
    unsigned int x          = cluster_xy >> Y_WIDTH;
    unsigned int y          = cluster_xy & ((1<<Y_WIDTH)-1);

    while(1)
    {
        // initialize counter
        unsigned int count = GIET_IDLE_TASK_PERIOD;

        // decounting loop
        asm volatile(
                "move   $3,   %0              \n"
                "_idle_task_loop:             \n"
                "addi   $3,   $3,   -1        \n"
                "bnez   $3,   _idle_task_loop \n"
                "nop                          \n"
                :
                : "r"(count)
                : "$3" ); 

        // warning message
        _printf("\n[GIET WARNING] Processor[%d,%d,%d] still idle at cycle %d\n",
                x, y, lpid, _get_proctime() );
    }
} // end ctx_idle()


/////////////////////////////////////////////////////////////////////////////////
// The address of this function is used to initialise the return address
// in the "idle" task context.
/////////////////////////////////////////////////////////////////////////////////
void _ctx_eret() 
{
    asm volatile("eret");
}


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