Changes between Initial Version and Version 1 of kernel_switch

Timestamp:

Oct 23, 2014, 11:34:07 AM (10 years ago)

Author:

alain

Comment:

--

kernel_switch

@@ +1 @@
+= GIET-VM / Context Switch Handler =
+
+[[PageOutline]]
+
+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.
+
+A task context is an array of 64 words = 256 bytes. 
+It contains copies of processor registers (when the task is preempted):
+ * GPR[i] : generally stored in slot (i). $0, $26 & $27 are not saved.
+ * HI & LO registers : used by multiply/divide instructions.
+ * CP0 registers : EPC, SR, CR, BVAR 
+ * CP2 registers : PTPR 
+It contains some general informations associated to the task:
+ * TTY    : TTY channel global index
+ * NIC    : NIC channel global index
+ * CMA    : CMA channel global index
+ * HBA    : HBA channel global index
+ * DMA    : DMA channel local index
+ * TIM    : TIM channel local index
+ * PTAB   : page table virtual base address 
+ * LTID   : Task local index (in scheduler)
+ * VSID   : Virtual space index
+ * RUN    : Task state (0 => sleeping / 1 => runnable ) 
+ * TRDID  : Thread ID index (in vspace)
+
+|| [0] ***   || [8]   $8    || [16] $16   || [24] $24  || [32] EPC   || [40] TTY   || [48] TRDID ||
+|| [1] $1    || [9]   $9    || [17] $17  || [25] $25  || [33] CR     || [41] DMA  || [49] ***      ||
+|| [2] $2    || [10] $10  || [18] $18  || [26]  LO   || [34] SR      || [42] NIC   || [50] ***      ||
+|| [3] $3    || [11] $11  || [19] $19  || [27]  HI    || [35] BVAR  || [43] TIM  || [51] ***      ||
+|| [4] $4    || [12] $12  || [20] $20  || [28] $28  || [36] PTAB  || [44] HBA  || [52] ***      ||
+|| [5] $5    || [13] $13  || [21] $21  || [29] SP     || [37] LTID  || [45] CMA || [53] ***      ||
+|| [6] $6    || [14] $14  || [22] $22  || [30] $30  || [38] VSID  || [46] GTID || [54] ***      ||   
+|| [7] $7    || [15] $15  || [23] $23  || [31] RA    || [39] PTPR   || [47] RUN  || [55] ***      ||
+
+
+
+ === void _ctx_switch() ===
+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).
+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.
+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_eret() ===
+The address of this function is used to initialise the return address in the "idle" task context.
+
+ === void _idle_task() ===
+This function is executed task when no other task can be executed.
+
+
+