task的TCB結構：

typedef struct TC_TCB_STRUCT

{

????/* Standard thread information first. This information is used by

???????the target dependent portion of this component. Changes made

???????to this area of the structure can have undesirable side effects. */

????CS_NODE tc_created; /* Node for linking to */ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //鏈接指向創建task鏈表

???????????????????????????????????????????????/* created task list */

????UNSIGNED tc_id; /* Internal TCB ID */

????CHAR tc_name[NU_MAX_NAME]; /* Task name */

????DATA_ELEMENT tc_status; /* Task status */

????BOOLEAN tc_delayed_suspend; /* Delayed task suspension*/

????DATA_ELEMENT tc_priority; /* Task priority */

????BOOLEAN tc_preemption; /* Task preemption enable */ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//是否搶占

????UNSIGNED tc_scheduled; /* Task scheduled count */

????UNSIGNED tc_cur_time_slice; /* Current time slice */

????VOID *tc_stack_start; /* Stack starting address */ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //棧起始地址

????VOID *tc_stack_end; /* Stack ending address */

????VOID *tc_stack_pointer; /* Task stack pointer */

????UNSIGNED tc_stack_size; /* Task stack's size */

????UNSIGNED tc_stack_minimum; /* Minimum stack size */

????struct TC_PROTECT_STRUCT

???????????????????????*tc_current_protect; /* Current protection */

????VOID *tc_saved_stack_ptr; /* Previous stack pointer */

????UNSIGNED tc_time_slice; /* Task time slice value */

????/* Information after this point is not used in the target dependent

???????portion of this component. Hence, changes in the following section

???????should not impact assembly language routines. */

????struct TC_TCB_STRUCT

???????????????????????*tc_ready_previous, /* Previously ready TCB */ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //指向上一個TCB

???????????????????????*tc_ready_next; /* next and previous ptrs */ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //指向下一個TCB

????/* Task control information follows. */

????UNSIGNED tc_priority_group; /* Priority group mask bit*/

????struct TC_TCB_STRUCT

??????????????????????**tc_priority_head; /* Pointer to list head */ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//指向TCB鏈表頭

????DATA_ELEMENT *tc_sub_priority_ptr; /* Pointer to sub-group */

????DATA_ELEMENT tc_sub_priority; /* Mask of sub-group bit */

????DATA_ELEMENT tc_saved_status; /* Previous task status */

????BOOLEAN tc_signal_active; /* Signal active flag */

#if PAD_3

????DATA_ELEMENT tc_padding[PAD_3];

#endif

???????????????????????????????????????????????/* Task entry function */

????VOID (*tc_entry)(UNSIGNED, VOID *); ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//task入口函數，下面是參數

????UNSIGNED tc_argc; /* Optional task argument */

????VOID *tc_argv; /* Optional task argument */

????VOID (*tc_cleanup) (VOID *);/* Clean-up routine */

????VOID *tc_cleanup_info; /* Clean-up information */

????struct TC_PROTECT_STRUCT

???????????????????????*tc_suspend_protect; /* Protection at time of */

???????????????????????????????????????????????/* task suspension */

????/* Task timer information. */ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//計時器

????INT tc_timer_active; /* Active timer flag */

????TM_TCB tc_timer_control; /* Timer control block */

????/* Task signal control information. */

????UNSIGNED tc_signals; /* Current signals */

????UNSIGNED tc_enabled_signals; /* Enabled signals */

????/* tc_saved_status and tc_signal_active are now defined above in an

???????attempt to keep DATA_ELEMENT types together. */

????/* Signal handling routine. */ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //signal中斷處理？

????VOID (*tc_signal_handler) (UNSIGNED);

????/* Reserved words for the system and a single reserved word for the

???????application. */

????UNSIGNED tc_system_reserved_1; /* System reserved word */

????UNSIGNED tc_system_reserved_2; /* System reserved word */

????UNSIGNED tc_system_reserved_3; /* System reserved word */

????UNSIGNED tc_app_reserved_1; /* Application reserved */

????/* This information is accessed in assembly */

#if ((NU_SUPERV_USER_MODE == 1)||(NU_MODULE_SUPPORT == 1))

????UNSIGNED tc_su_mode; /* Supervisor/User mode indicator */

????UNSIGNED tc_module; /* Module identifier */

#endif

} TC_TCB;

TCC創建任務函數：

STATUS TCC_Create_Task(NU_TASK *task_ptr, CHAR *name,

??????????VOID (*task_entry)(UNSIGNED, VOID *), UNSIGNED argc, VOID *argv,

??????????VOID *stack_address, UNSIGNED stack_size,

??????????OPTION priority, UNSIGNED time_slice,

??????????OPTION preempt, OPTION auto_start)

{

R1 TC_TCB *task; /* Task control block ptr */

R2 INT i; /* Working index variable */

STATUS status = NU_SUCCESS;

NU_SUPERV_USER_VARIABLES

????/* Switch to supervisor mode */

????NU_SUPERVISOR_MODE();

????/* Move input task pointer into internal pointer. */

????task = (TC_TCB *) task_ptr;

#ifdef NU_ENABLE_STACK_CHECK

????/* Call stack checking function to check for an overflow condition. */

????TCT_Check_Stack();

#endif

#ifdef NU_ENABLE_HISTORY

????/* Make an entry that corresponds to this function in the system history

???????log. */

????HIC_Make_History_Entry(NU_CREATE_TASK_ID, (UNSIGNED) task,

????????????????????????????????(UNSIGNED) name, (UNSIGNED) task_entry);

#endif

????/* First, clear the task ID just in case it is an old Task

???????Control Block. */

????task -> tc_id = 0;

????/* Fill in the task name. */

????for (i = 0; i < NU_MAX_NAME; i++)

????????task -> tc_name[i] = name[i];

????/* Fill in the basic task information. */

????task -> tc_entry = task_entry;

????task -> tc_argc = argc;

????task -> tc_argv = argv;

????task -> tc_status = NU_PURE_SUSPEND; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //這里設定為pure_suspend,完全掛起。如果設定auto_start，調用resume_task()喚醒task

????task -> tc_delayed_suspend = NU_FALSE;

????task -> tc_scheduled = 0;

????task -> tc_time_slice = time_slice;

????task -> tc_cur_time_slice = time_slice;

????task -> tc_current_protect = NU_NULL;

????task -> tc_suspend_protect = NU_NULL;

????task -> tc_cleanup = NU_NULL;

????task -> tc_cleanup_info = NU_NULL;

????/* Setup task's preemption posture. */

????if (preempt == NU_PREEMPT)

????????task -> tc_preemption = NU_TRUE;

????else

????????task -> tc_preemption = NU_FALSE;

????/* Fill in information about the task's stack. */

????task -> tc_stack_start = stack_address;

????task -> tc_stack_end = 0;

????task -> tc_stack_size = stack_size;

????task -> tc_stack_minimum = stack_size;

????/* Setup priority information for the task. There are two bit maps

???????associated with each task. The first bit map indicates which group

???????of 8-priorities it is. The second bit map indicates the actual

???????priority within the group. */

????task -> tc_priority = priority; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ??

????task -> tc_priority_head = &(TCD_Priority_List[priority]); ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//這里掛載進TCB雙向鏈表指針

????task -> tc_sub_priority = (DATA_ELEMENT) (1 << (priority & 7));

????priority = priority >> 3;

????task -> tc_priority_group = ((UNSIGNED) 1) << priority;

????task -> tc_sub_priority_ptr = &(TCD_Sub_Priority_Groups[priority]);

????/* Initialize link pointers. */

????task -> tc_created.cs_previous = NU_NULL;

????task -> tc_created.cs_next = NU_NULL;

????task -> tc_ready_previous = NU_NULL;

????task -> tc_ready_next = NU_NULL;

????/* Build a stack frame for this task by calling TCT_Build_Task_Stack. */

????TCT_Build_Task_Stack(task);

????/* Initialize the signal information of the task. */

????task -> tc_signals = 0;

????task -> tc_enabled_signals = 0;

????task -> tc_signal_handler = 0;

????task -> tc_signal_active = NU_FALSE;

????/* Initialize additional kernel options data */

#if (NU_SUPERV_USER_MODE == 1)

????task->tc_su_mode = 0; /* Initially in User mode */

????task->tc_module = 0; /* Not initially bound to a module */

#endif

????/* Initialize the task timer. */

????task -> tc_timer_active = NU_FALSE;

????TMC_Init_Task_Timer(&(task -> tc_timer_control), (VOID *) task);

????/* Protect the list of created tasks. */

????TCT_Protect(&TCD_List_Protect);

????/* At this point the task is completely built. The ID can now be

???????set and it can be linked into the created task list. */

????task -> tc_id = TC_TASK_ID;

#if defined(NU_MODULE_SUPPORT) && (NU_MODULE_SUPPORT > 0)

????/* If executing in a thread's context, bind to that thread's module */

????if(TCD_Current_Thread != NU_NULL)

????{

????????status = MSC_Bind_Module_Task(

??????????(MS_MODULE*)(((TC_TCB*)(TCD_Current_Thread))->tc_module), task);

????}

????else /* It must be initialization time, so use the current module */

????{

????????status = MSC_Bind_Module_Task(msd_current_module, task);

????}

#endif /* NU_MODULE_SUPPORT */

????/* Link the task into the list of created tasks and increment the

???????total number of tasks in the system. */

????CSC_Place_On_List(&TCD_Created_Tasks_List, &(task -> tc_created));

????TCD_Total_Tasks++;

#ifdef INCLUDE_PROVIEW

????_RTProf_DumpTask(task,RT_PROF_CREATE_TASK);

#endif

????/* Release the protection. */

????TCT_Unprotect();

????/* Determine if the task should be automatically started. */

????if (auto_start == NU_START)

????{

????????/* Protect the system data structures. */

????????TCT_Protect(&TCD_System_Protect);

????????/* Start the task by resuming it. If the preemption is required,

???????????leave the current task. */

????????if (TCC_Resume_Task(task_ptr, NU_PURE_SUSPEND))

????????????/* Transfer control back to the system. */

????????????TCT_Control_To_System();

????????else

????????????/* Release the protection. */

????????????TCT_Unprotect();

????}

????/* Return to user mode */

????NU_USER_MODE();

????/* Return successful completion. */

????return(status);

}

TCC創建HISR函數：

STATUS TCC_Create_HISR(NU_HISR *hisr_ptr, CHAR *name,

??????????VOID (*hisr_entry)(VOID), OPTION priority,

??????????VOID *stack_address, UNSIGNED stack_size)

{

R1 TC_HCB *hisr; /* HISR control block ptr */

R2 INT i; /* Working index variable */

STATUS status = NU_SUCCESS;

NU_SUPERV_USER_VARIABLES

????/* Switch to supervisor mode */

????NU_SUPERVISOR_MODE();

????/* Move input HISR pointer into internal pointer. */

????hisr = (TC_HCB *) hisr_ptr;

#ifdef NU_ENABLE_STACK_CHECK

????/* Call stack checking function to check for an overflow condition. */

????TCT_Check_Stack();

#endif

#ifdef NU_ENABLE_HISTORY

????/* Make an entry that corresponds to this function in the system history

???????log. */

????HIC_Make_History_Entry(NU_CREATE_HISR_ID, (UNSIGNED) hisr,

????????????????????????????????(UNSIGNED) name, (UNSIGNED) hisr_entry);

#endif

????/* First, clear the HISR ID just in case it is an old HISR

???????Control Block. */

????hisr -> tc_id = 0;

????/* Fill in the HISR name. */

????for (i = 0; i < NU_MAX_NAME; i++)

????????hisr -> tc_name[i] = name[i];

????/* Fill in the basic HISR information. */

????hisr -> tc_entry = hisr_entry;

????hisr -> tc_scheduled = 0;

????hisr -> tc_activation_count = 0;

????hisr -> tc_cur_time_slice = 0;

????/* Fill in information about the HISR's stack. */

????hisr -> tc_stack_start = stack_address;

????hisr -> tc_stack_end = 0;

????hisr -> tc_stack_size = stack_size;

????hisr -> tc_stack_minimum = stack_size;

????/* Setup priority information for the HISR. Priorities range from 0 to

???????TC_HISR_PRIORITIES - 1. */

????hisr -> tc_priority = priority & 3; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //這里優先級與上了3，所以只有0、1、2三種。優先級會更高

????/* Initialize link pointers. */

????hisr -> tc_created.cs_previous = NU_NULL; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //這里不加雙向鏈表

????hisr -> tc_created.cs_next = NU_NULL;

????hisr -> tc_active_next = NU_NULL;

????/* Clear protect pointer. */

????hisr -> tc_current_protect = NU_NULL;

????/* Initialize additional kernel options data */

#if (NU_SUPERV_USER_MODE == 1)

????hisr->tc_su_mode = 1; /* TCT_HISR_Shell in Supervisor mode */

????hisr->tc_module = 0; /* Not initially bound to a module */

#endif

????/* Build a stack frame for this HISR by calling TCT_Build_HISR_Stack. */

????TCT_Build_HISR_Stack(hisr);

????/* Protect the list of created HISRs. */

????TCT_Protect(&TCD_HISR_Protect);

????/* At this point the HISR is completely built. The ID can now be

???????set and it can be linked into the created HISR list. */

????hisr -> tc_id = TC_HISR_ID;

#if defined(NU_MODULE_SUPPORT) && (NU_MODULE_SUPPORT > 0)

????/* If executing in a thread's context, bind to that thread's module */

????if(TCD_Current_Thread != NU_NULL)

????{

????????status = MSC_Bind_Module_HISR(

??????????(MS_MODULE*)(((TC_TCB*)(TCD_Current_Thread))->tc_module), hisr);

????}

????else /* It must be initialization time, so use the current module */

????{

????????status = MSC_Bind_Module_HISR(msd_current_module, hisr);

????}

#endif /* NU_MODULE_SUPPORT */

????/* Link the HISR into the list of created HISRs and increment the

???????total number of HISRs in the system. */

????CSC_Place_On_List(&TCD_Created_HISRs_List, &(hisr -> tc_created)); ? ? ? ? ? ? ? ? ? ? ? ? ? //在這里加入了鏈表？

????TCD_Total_HISRs++; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //增加了鏈表長度計數

#ifdef INCLUDE_PROVIEW

????_RTProf_DumpHisr(hisr,RT_PROF_CREATE_HISR);

#endif

????/* Release the protection. */

????TCT_Unprotect();

????/* Return to user mode */

????NU_USER_MODE();

????/* Return successful completion. */

????return(status);

}

在tct.s中有TCT_Control_To_System，主要要建立新的system_stack:

;************************************************************************

;*

;* FUNCTION

;*

;* TCT_Control_To_System

;*

;* DESCRIPTION

;*

;* This function returns control from a thread to the system. Note

;* that this service is called in a solicited manner, i.e. it is

;* not called from an interrupt thread. Registers required by the

;* compiler to be preserved across function boundaries are saved by

;* this routine. Note that this is usually a sub-set of the total

;* number of available registers.

;*

;* CALLED BY

;*

;* Other Components

;*

;* CALLS

;*

;* TCT_Schedule Schedule the next thread

;*

;* INPUTS

;*

;* None

;*

;* OUTPUTS

;*

;* None

;*

;* HISTORY

;*

;* NAME DATE REMARKS

;*

;* W. Lamie 02-15-1994 Created initial version 1.0

;* D. Lamie 02-15-1994 Verified version 1.0

;* C. Meredith 03-01-1994 Corrected problem in time-slice

;* reset logic, resulting in

;* version 1.1

;* D. Lamie 03-18-1994 Verified version 1.1

;*

;************************************************************************

;VOID TCT_Control_To_System(void)

;{

????.def $TCT_Control_To_System

$TCT_Control_To_System ; Dual-state interworking veneer

????.state16

????BX r15

????NOP

????.state32

????B _TCT_Control_To_System

????????.def _TCT_Control_To_System

_TCT_Control_To_System

????; Lockout interrupts.

????????MRS r0,CPSR ; Pickup current CPSR ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //獲取CPSR值

????????ORR r0,r0,#LOCKOUT ; Build interrupt lockout value

????????MSR CPSR,r0 ; Lockout interrupts ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//寫入CPSR中斷屏蔽位

????; Save a minimal context of the thread.

????????STMDB r13!,{r4-r12,r14} ; Save minimal context of thread on ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //保存上下文

????????????????????????????????????????????; the current stack

????????.if THUMB ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //如果是THUMB模式

?????????

?????????MOV r2,r14 ; Determine what state the caller

?????????MOV r2,r2,LSL #31 ; was in and build an

?????????MOV r2,r2,LSR #26 ; appropriate state mask

?????????STR r2,[r13, #-4]! ; Place it on the stack

?????????

????????.endif

????????MOV r2,#0 ; Build solicited stack type value ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//建立solicited stack（請求棧？）

????????????????????????????????????????????; and NU_NULL value

????????STR r2,[r13, #-4]! ; Place it on the top of the stack ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //用r2替換r13下面一格的內容，r2不是0嗎。那不是刪除了r4的內容嗎？

????; Setup a pointer to the thread control block.

; REG_Thread_Ptr = (TC_TCB *) TCD_Current_Thread;

????????LDR r1,Current_Thread ; Pickup current thread ptr address ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//獲取當前進程指針地址

????????LDR r0,[r1, #0] ; Pickup current thread pointer

????; Clear the current thread control block pointer.

; TCD_Current_Thread = NU_NULL;

????????LDR r3,Slice_State ; Pickup time slice state address ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //獲取time Slice_State地址

????????STR r2,[r1, #0] ; Set current thread pointer to ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//又把進程指針清零了

????????????????????????????????????????????; NU_NULL

; Check to see if a time slice is active. If so, copy the original time

; slice into the current time slice field of the task's control block.

; if (TMD_Time_Slice_State == 0)

; {

????????LDR r1,[r3, #0] ; Pickup time slice state flag ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //r3是Slice_State中的值到r1

????????CMP r1,#0 ; Compare with active value ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//比較是否是0

????????BNE TCT_No_Stop_TS_1 ; If non-active, don't disable ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//如果不是0，跳轉到TCT_No_Stop_TS_1

????

????; Insure that the next time the task runs it gets a fresh time

????; slice.

; REG_Thread_Ptr -> tc_cur_time_slice = REG_Thread_Ptr -> tc_time_slice;

????????LDR r1,[r0, #40h] ; Pickup original time slice ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //從另一個地方找了time slice

????????; Clear any active time slice by setting the state to NOT_ACTIVE.

; TMD_Time_Slice_State = 1;

????????MOV r2,#1 ; Build disable value ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //設置了1關閉

????????STR r2,[r3, #0] ; Disable time slice ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//設置time_slice_state

????????STR r1,[r0, #20h] ; Reset current time slice ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//明明已經禁止了為什么還要賦值current time_slice呢。

; }

TCT_No_Stop_TS_1: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ??//這里是TCT_No_Stop_TS_1

?????; Save off the current stack pointer in the control block.

; REG_Thread_Ptr -> tc_stack_pointer = (VOID *) REG_Stack_Ptr;

????????STR r13,[r0, #2ch] ; Save the thread's stack pointer ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//保存進程棧指針，為什么Slice_State加上#2ch就是進程棧指針呢，可能是結構體向下移動了幾位

?????; Clear the task's current protection.

; (REG_Thread_Ptr -> tc_current_protect) -> tc_tcb_pointer = NU_NULL;

; REG_Thread_Ptr -> tc_current_protect = NU_NULL;

????????LDR r1,[r0, #38h] ; Pickup current thread pointer ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //獲取當前進程指針

????????MOV r2,#0 ; Build NU_NULL value ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //r2置0

????????STR r2,[r0, #38h] ; Clear the protect pointer field ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //清除保護指針字段

????????STR r2,[r1, #0] ; Release the actual protection ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //釋放實際保護

????; Switch to the system stack.

; REG_Stack_Ptr = TCD_System_Stack;

????????LDR r1, System_Stack ; Pickup address of stack pointer ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//這里應該建立了新的system棧

????????LDR r2, System_Limit ; Pickup address of stack limit ptr

????????LDR r13,[r1, #0] ; Switch to system stack

????????LDR r10,[r2, #0] ; Setup system stack limit

????; Finished, return to the scheduling loop.

????????B _TCT_Schedule ; Return to scheduling loop ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //跳轉到_TCT_Schedule

;}

在tct.s中有TCT_Schedule(void)內容，這里開關的中斷屏蔽寄存器，來使得進程能跟切換（進程指針的獲取）：

;************************************************************************

;*

;* FUNCTION

;*

;* TCT_Schedule

;*

;* DESCRIPTION

;*

;* This function waits for a thread to become ready. Once a thread

;* is ready, this function initiates a transfer of control to that

;* thread.

;*

;* CALLED BY

;*

;* INC_Initialize Main initialization routine

;*

;* CALLS

;*

;* TCT_Control_To_Thread Transfer control to a thread

;*

;* INPUTS

;*

;* TCD_Execute_Task Pointer to task to execute

;*

;* OUTPUTS

;*

;* None

;*

;* HISTORY

;*

;* NAME DATE REMARKS

;*

;* W. Lamie 02-15-1994 Created initial version 1.0

;* D. Lamie 02-15-1994 Verified version 1.0

;*

;************************************************************************

;VOID TCT_Schedule(void)

;{

????.def $TCT_Schedule

$TCT_Schedule ; Dual-state interworking veneer

????.state16 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //16位模式下？

????BX r15

????NOP

????.state32 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //32位模式下

????B _TCT_Schedule

????????.def _TCT_Schedule

_TCT_Schedule ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//明明下面就是_TCT_Schedule為什么要跳轉

????; Restore interrupts according to the value contained in ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //根據在TCD_Interrupt_Level中值恢復中斷?

; TCD_Interrupt_Level.

????????LDR r1,Int_Level ; Build address of interrupt level ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//把Int_Level地址讀取到r1? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

????????MRS r0,CPSR ; Pickup current CPSR ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//讀取CPSR到r0

????????LDR r2,[r1, #0] ; Pickup current interrupt lockout ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //獲取當前中斷屏蔽字段

????????BIC r0,r0,#LOCK_MSK ; Clear the interrupt lockout bits ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //清除中斷屏蔽

????????ORR r0,r0,r2 ; Build new interrupt lockout CPSR ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//設置新的中斷屏蔽字段

????????MSR CPSR,r0 ; Setup new CPSR ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //寫回CPSR

????????LDR r2,Execute_HISR ; Pickup TCD_Execute_HISR address ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//獲取TCD_Execute_HISR地址到r2

????????LDR r3,Execute_Task ; Pickup TCD_Execute_Task address ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//獲取TCD_Execute_Task地址到r3

????.if $$isdefed("INCLUDE_PROVIEW")

; Nucleus ProView Hook

; We check if upon entering TCT_Schedule we already have a task to excute. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //確認是否進入了TCT_Schedule時已經運行了task

; if not, we start IDLE. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //如果沒運行就空閑

????????LDR r0,[r2, #0] ; Pickup highest priority HISR ptr ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //獲取最高有限級的HISR指針

????????CMP r0,#0 ; Is there a HISR active? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//是否已經運行，0是運行

????????BNE TCT_Schedule_Thread ; Found an HISR ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//建立一個HISR，下面是TCT_Schedule_Thread

????????LDR r0,[r3, #0] ; Pickup highest priority Task ptr ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //獲取任務的最高優先級

????????CMP r0,#0 ; Is there a task active? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//判斷是否運行

????????BNE TCT_Schedule_Thread ; If not, start IDLE. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//不是0就開始IDLE

????????STR r2,[r13, #-4]! ; Save r2 on the stack ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//把r2壓入棧Execute_HISR地址

????????STR r3,[r13, #-4]! ; Save r3 on the stack ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//把r3壓入棧Execute_Task地址

????????BL __NU_Idle_Hook ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//跳轉到__NU_IDLE_HOOK這個是進等待吧，鉤子

????????LDR r3,[r13], #4 ; Recover r2

????????LDR r2,[r13], #4 ; Recover r3

????.endif

????; Wait until a thread (task or HISR) is available to execute.

; do

; {

TCT_Schedule_Loop:

; } while ((!TCD_Execute_HISR) && (!TCD_Execute_Task)); ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //TCD_Execute_HISR或TCD_Execute_Task為空就一直IDLE

????????LDR r0,[r2, #0] ; Pickup highest priority HISR ptr

????????CMP r0,#0 ; Is there a HISR active?

????????BNE TCT_Schedule_Thread ; Found an HISR

????????LDR r0,[r3, #0] ; Pickup highest priority Task ptr

????????CMP r0,#0 ; Is there a task active?

????????BEQ TCT_Schedule_Loop ; If not, continue the search

????; Yes, either a task or an HISR is ready to execute. Lockout

????; interrupts while the thread is transferred to.

TCT_Schedule_Thread: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//這里應該是調度任務了

????????MRS r1,CPSR ; Pickup CPSR again ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //獲取CPSR

????????ORR r1,r1,#LOCKOUT ; Build interrupt lockout value ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//進行邏輯或設置中斷屏蔽值

????????MSR CPSR,r1 ; Lockout interrupts ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//為什么設置了中斷屏蔽就會運行了，是不是通過開關中斷屏蔽，來讓任務自動搶占？上面獲取了HISR最高優先級的指針地址

; Transfer control to the thread by falling through to the following

; routine.

;}

control_to_thread,只要確認了time slice有沒有正常工作。:

;************************************************************************

;*

;* FUNCTION

;*

;* TCT_Control_To_Thread

;*

;* DESCRIPTION

;*

;* This function transfers control to the specified thread. Each

;* time control is transferred to a thread, its scheduled counter

;* is incremented. Additionally, time-slicing for task threads is

;* enabled in this routine. The TCD_Current_Thread pointer is

;* setup by this function.

;*

;* CALLED BY

;*

;* TCT_Schedule Indirectly called

;* TCT_Protect Protection task switch

;*

;* CALLS

;*

;* None

;*

;* INPUTS

;*

;* thread Thread control block pointer

;*

;* OUTPUTS

;*

;* None

;*

;* HISTORY

;*

;* NAME DATE REMARKS

;*

;* W. Lamie 02-15-1994 Created initial version 1.0

;* D. Lamie 02-15-1994 Verified version 1.0

;*

;************************************************************************

;VOID TCT_Control_To_Thread(TC_TCB *thread)

;{

_TCT_Control_To_Thread

????; Setup the current thread pointer.

; TCD_Current_Thread = (VOID *) thread; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//設置當前進程指針

????????LDR r1,Current_Thread ; Pickup current thread ptr address

????????LDR r2,[r0, #1ch] ; Pickup scheduled count

????????STR r0,[r1, #0] ; Setup current thread pointer

????; Increment the thread scheduled counter.

; thread -> tc_scheduled++; ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//增加scheduled計數

????????LDR r3,[r0, #20h] ; Pickup time slice value

????????ADD r2,r2,#1 ; Increment the scheduled count

????????STR r2,[r0, #1ch] ; Store new scheduled count

????; Check for time slice option.

; if (thread -> tc_cur_time_slice) ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //確認time_slice

; {

????????CMP r3,#0 ; Is there a time slice?

????????BEQ TCT_No_Start_TS_1 ; If 0, there is no time slice ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //如果是0，表明沒有。time slice沒有運行

????????; Start a time slice.

; TMD_Time_Slice = thread -> tc_cur_time_slice;

; TMD_Time_Slice_State = 0;

????????LDR r2,Time_Slice ; Pickup address of TMD_Time_Slice ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//獲取time slice

????????LDR r1,Slice_State ; Pickup address of? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //獲取time slice state

????????????????????????????????????????????; TMD_Time_Slice_State

????????STR r3,[r2, #0] ; Setup the time slice ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//設置time slice

????????MOV r2,#0 ; Build active state flag ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //置0

????????STR r2,[r1,#0] ; Set the active flag ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//設置活動標志

; }

TCT_No_Start_TS_1: ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//這里是TCT_No_Start_TS_1

????.if $$isdefed("INCLUDE_PROVIEW") ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//如果定義了INCLUDE_PROVIEW

; Nucleus ProView Hook

????????STR r0,[r13, #-4]! ; Save r0 on the stack ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//把r0壓入棧

????????BL __NU_Schedule_Task_Hook ; Branch to RTView ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?//跳轉到__NU_Schedule_Task_Hook?

????????LDR r0,[r13], #4 ; Recover return address

????.endif

????; Pickup the stack pointer and resume the thread.

; REG_Stack_Ptr = thread -> tc_stack_pointer;

????????LDR r13,[r0, #2ch] ; Switch to thread ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? //運行新的thread

?
?任務的切換主要是上下文的切換，也就是task棧的切換，函數的調用會保存部分regs和返回地址，這些動作都是編譯器來完成的，而OS中的任務切換是運行時（runtime）的一種狀態變化，因此編譯器也無能為力，所以對于上下文的保存需要代碼來實現。
?
?任務的搶占是異步的因此必須要通過中斷來實現，一般每次timer的中斷決定當前的task的slice time是否expired，然后設置TCT_Set_Execute_Task為相同優先級的其他task或更高優先級的task；高優先級的task搶占低優先級的task，一般是外部中斷觸發，在HISR中resume_task()喚醒高優先級的task，然后schedule到高優先級的task中，因為timer的HISR是在系統初始化就已經注冊的，只是執行timeout和time slice超時后的操作，并沒有執行resume_task的動作。

http://blog.chinaunix.net/uid-22003667-id-3291833.html

轉載于:https://www.cnblogs.com/ch122633/p/7363282.html

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