source: soft/giet_vm/giet_kernel/ctx_handler.c @ 313

Last change on this file since 313 was 294, checked in by alain, 11 years ago

Introducing support for IOPIC component.

  • Property svn:executable set to *
File size: 4.9 KB
Line 
1//////////////////////////////////////////////////////////////////////////////////
2// File     : ctx_handler.c
3// Date     : 01/04/2012
4// Authors  : alain greiner & joel porquet
5// Copyright (c) UPMC-LIP6
6//////////////////////////////////////////////////////////////////////////////////
7
8#include <giet_config.h>
9#include <tim_driver.h>
10#include <xcu_driver.h>
11#include <tty_driver.h>
12#include <utils.h>
13#include <ctx_handler.h>
14#include <mapping_info.h>
15#include <sys_handler.h>
16
17extern void _task_switch(unsigned int *, unsigned int *);
18
19/////////////////////////////////////////////////////////////////////////////////
20// This function performs a context switch between the running task
21// and  another task, using a round-robin sheduling policy between all
22// tasks allocated to a given processor (static allocation).
23// It selects the next runable task to resume execution.
24// If the only runable task is the current task, return without context switch.
25// If there is no runable task, the scheduler switch to the default "idle" task.
26/////////////////////////////////////////////////////////////////////////////////
27// Implementation note
28// The return address contained in $31 is saved in the current task context
29// (in the ctx[31] slot), and the function actually returns to the address
30// contained in the ctx[31] slot of the next task context.
31/////////////////////////////////////////////////////////////////////////////////
32void _ctx_switch() 
33{
34    unsigned int gpid       = _get_procid();
35    unsigned int cluster_xy = gpid / NB_PROCS_MAX;
36    unsigned int lpid       = gpid % NB_PROCS_MAX;
37
38    // get scheduler address
39    static_scheduler_t* psched = (static_scheduler_t*)_get_sched();
40
41    // get number of tasks allocated to scheduler
42    unsigned int tasks = psched->tasks;
43
44    // get current task index
45    unsigned int curr_task_id = psched->current;
46
47    // select the next task using a round-robin policy
48    unsigned int next_task_id;
49    unsigned int tid;
50    unsigned int found = 0;
51
52    for (tid = curr_task_id + 1; tid < curr_task_id + 1 + tasks; tid++) 
53    {
54        next_task_id = tid % tasks;
55        // test if the task is runable
56        if ( psched->context[next_task_id][CTX_RUN_ID] ) 
57        {
58            found = 1;
59            break;
60        }
61    }
62
63    // launch "idle" task if no runable task
64    if (found == 0) 
65    {
66        next_task_id = IDLE_TASK_INDEX;
67    }
68
69#if GIET_DEBUG_SWITCH
70unsigned int x = cluster_xy >> Y_WIDTH;
71unsigned int y = cluster_xy & ((1<<Y_WIDTH)-1);
72
73_printf("\n[TASK SWITCH] (%d) -> (%d) on processor[%d,%d,%d] at cycle %d\n",
74        curr_task_id, next_task_id, x, y , lpid, _get_proctime() );
75#endif
76
77    if (curr_task_id != next_task_id)  // actual task switch required
78    {
79        unsigned int* curr_ctx_vaddr = &(psched->context[curr_task_id][0]);
80        unsigned int* next_ctx_vaddr = &(psched->context[next_task_id][0]);
81
82        // reset timer counter. In each cluster,
83        // the NB_PROCS_MAX timers are system timers (TICK)
84
85#if USE_XICU
86        _xcu_timer_reset_cpt( cluster_xy, lpid );
87#else
88        _timer_reset_cpt( cluster_xy, lpid); 
89#endif
90
91        // set current task index
92        psched->current = next_task_id;
93
94        // makes context switch
95        _task_switch(curr_ctx_vaddr, next_ctx_vaddr);
96    }
97} //end _ctx_switch()
98
99/////////////////////////////////////////////////////////////////////////////////////
100// This function is executed as the"idle" task when no other task can be executed
101/////////////////////////////////////////////////////////////////////////////////////
102void _idle_task() 
103{
104    while(1)
105    {
106        unsigned int count = GIET_IDLE_TASK_PERIOD;
107
108        // decounting loop
109        asm volatile(
110                "move   $3,   %0              \n"
111                "_idle_task_loop:             \n"
112                "addi   $3,   $3,   -1        \n"
113                "bnez   $3,   _idle_task_loop \n"
114                "nop                          \n"
115                :
116                : "r"(count)
117                : "$3" ); 
118
119        // warning message
120        unsigned int gpid       = _get_procid();
121        unsigned int cluster_xy = gpid / NB_PROCS_MAX;
122        unsigned int lpid       = gpid % NB_PROCS_MAX;
123        unsigned int x          = cluster_xy >> Y_WIDTH;
124        unsigned int y          = cluster_xy & ((1<<Y_WIDTH)-1);
125
126        _printf("\n[GIET WARNING] Processor[%d,%d,%d] still idle at cycle %d\n",
127                x, y, lpid, _get_proctime() );
128
129    }
130} // end ctx_idle()
131
132
133/////////////////////////////////////////////////////////////////////////////////
134// The address of this function is used to initialise the return address
135// in the "idle" task context.
136/////////////////////////////////////////////////////////////////////////////////
137void _ctx_eret() 
138{
139    asm volatile("eret");
140}
141
142
143// Local Variables:
144// tab-width: 4
145// c-basic-offset: 4
146// c-file-offsets:((innamespace . 0)(inline-open . 0))
147// indent-tabs-mode: nil
148// End:
149// vim: filetype=c:expandtab:shiftwidth=4:tabstop=4:softtabstop=4
150
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