Changes between Version 5 and Version 6 of kernel_context


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Timestamp:
Oct 23, 2014, 11:56:34 AM (10 years ago)
Author:
alain
Comment:

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  • kernel_context

    v5 v6  
    1 = GIET-VM / Context Switch Handler =
     1= GIET-VM / Task context access functions =
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    33[[PageOutline]]
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    5 The [source:soft/giet_vm/giet_kernel/ctx_handler.c ctx_handler.c] and [source:soft/giet_vm/giet_kernel/ctx_handler.h ctx_handler.h] files define the data structure and functions used to handle context switching. They are prefixed by "_" to remind that they can only be executed by a processor in kernel mode.
     5The [source:soft/giet_vm/giet_common/utils.c utils.c] and [source:soft/giet_vm/giet_common/utils.h utils.h] files define the functions used to access the task contexts. The codes used to identify the various context slots are defined [source:soft/giet_vm/giet_kernel/ctx_handler.h here].
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    7 A task context is an array of 64 words = 256 bytes.
    8 It contains copies of processor registers (when the task is preempted):
    9  * GPR[i] : generally stored in slot (i). $0, $26 & $27 are not saved.
    10  * HI & LO registers : used by multiply/divide instructions.
    11  * CP0 registers : EPC, SR, CR, BVAR
    12  * CP2 registers : PTPR
    13 It contains some general informations associated to the task:
    14  * TTY    : TTY channel global index
    15  * NIC    : NIC channel global index
    16  * CMA    : CMA channel global index
    17  * HBA    : HBA channel global index
    18  * DMA    : DMA channel local index
    19  * TIM    : TIM channel local index
    20  * PTAB   : page table virtual base address
    21  * LTID   : Task local index (in scheduler)
    22  * VSID   : Virtual space index
    23  * RUN    : Task state (0 => sleeping / 1 => runnable )
    24  * TRDID  : Thread ID index (in vspace)
     7These functions are prefixed by "_" to remind that they can only be executed by a processor in kernel mode.
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    26 || [0] ***   || [8]   $8    || [16] $16   || [24] $24  || [32] EPC   || [40] TTY   || [48] TRDID ||
    27 || [1] $1    || [9]   $9    || [17] $17  || [25] $25  || [33] CR     || [41] DMA  || [49] ***      ||
    28 || [2] $2    || [10] $10  || [18] $18  || [26]  LO   || [34] SR      || [42] NIC   || [50] ***      ||
    29 || [3] $3    || [11] $11  || [19] $19  || [27]  HI    || [35] BVAR  || [43] TIM  || [51] ***      ||
    30 || [4] $4    || [12] $12  || [20] $20  || [28] $28  || [36] PTAB  || [44] HBA  || [52] ***      ||
    31 || [5] $5    || [13] $13  || [21] $21  || [29] SP     || [37] LTID  || [45] CMA || [53] ***      ||
    32 || [6] $6    || [14] $14  || [22] $22  || [30] $30  || [38] VSID  || [46] GTID || [54] ***      ||   
    33 || [7] $7    || [15] $15  || [23] $23  || [31] RA    || [39] PTPR   || [47] RUN  || [55] ***      ||
     9
     10 === unsigned int '''_get_current_task_id'''( void ) ===
     11This function returns the local index of the currently running task.
     12
     13 === unsigned int '''_get_task_slot'''( unsigned int x,  unsigned int y,  unsigned int p, unsigned int ltid, unsigned int slot ) ===
     14This function returns the content of a context slot for any task running on any processor.
     15 * '''x''' : cluster x coordinate
     16 * '''y''' : cluster y coordinate
     17 * '''p''' : processor local index
     18 * '''ltid''' : task local index
     19 * '''slot''' : slot index
     20
     21 === void  '''_set_task_slot'''( unsigned int x, unsigned int y,  unsigned int p, unsigned int ltid, unsigned int slot,  unsigned int value ) ===
     22This function updates the content of a context slot for any task running on any processor.
     23 * '''x''' : cluster x coordinate
     24 * '''y''' : cluster y coordinate
     25 * '''p''' : processor local index
     26 * '''ltid''' : task local index
     27 * '''slot''' : slot index
     28
     29 === unsigned int '''_get_context_slot'''( unsigned int slot ) ===
     30This function returns the content of a context slot for the running task.
     31
     32 === void '''_set_context_slot'''( unsigned int slot,  unsigned int value ) ===
     33This function updates the content of a context slot for the running task.
    3434
    3535
    3636
    37  === void _ctx_switch() ===
    38 This function performs a context switch between the running (calling) task and  another runable task, using a round-robin sheduling policy between all tasks allocated to a given processor (static allocation).
    39 It selects the next runable task to resume execution.
    40 If the only runable task is the current task, return without context switch.
    41 If there is no runable task, the scheduler switch to the default "idle" task.
    42 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.
    43 
    44  === void _ctx_eret() ===
    45 The address of this function is used to initialise the return address in the "idle" task context.
    46 
    47  === void _idle_task() ===
    48 This function is executed task when no other task can be executed.
    49 
    50 
    51 
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