版本 2764c7927fe1c1b6c4379c4dea5dc4e782e836f5
FreeRTOS
組員
- 梁穎睿 / TheKK
- 李奇霖 / Shinshipower
- 方威迪 / waynew30777
- 陳盈伸 / shin21
共筆
Link<https://hackpad.com/FreeRTOSV8.0.0-PU3awKuzHz6#:h=%3Chardware-interfacing%3E>_
FreeRTOS架構
FreeRTOS是一個相對較小的應用程式。最小化的FreeRTOS內核僅包括3個（.c）文件和少數標頭檔，總共不到9000行程式碼，還包括了註解和空行。一個典型的編譯後（二進制）binary小於10KB。
FreeRTOS的程式碼可以分解為三個主要區塊：任務，通訊，和硬體界面。
●任務：大約有一半的FreeRTOS的核心程式碼用來處理多數作業系統首要關注的問題：任務。任務是給定優先權的用戶定義的C函數。 task.c和task.h完成了所有有關創造，排程，和維護任務的繁重工作。
●通訊：任務很重要，不過任務間可以互相通訊則更為重要！它給我們帶來FreeRTOS的第二項任務：通訊。大約40%的FreeRTOS核心程式碼是用來處理通訊的。 queue.c和queue.h是負責處理FreeRTOS的通訊的。任務和中斷使用隊列互相發送數據，並且使用semaphore和mutex來發送critical section的使用情況。
●硬體界面：接近9000行的程式碼拼湊起基本的FreeRTOS，是和硬體無關的；相同的程式碼都能夠運行，大約有6%的FreeRTOS的核心代碼，在硬體無關的FreeRTOS內核與硬體相關的程式碼間扮演著墊片的角色。我們將在下個部分討論硬體相關的程式碼。
硬體方面:
portmacro.h:
定義了硬體相關變數，如資料形態定義，以及硬體相關的函式呼叫的名稱定義(以portXXXXX爲名)等，統一各平臺呼叫函式的port.c:
定義了包含和硬體相關的程式碼的實作FreeRTOSConfig.h:
包含Clock speed, heap size, mutexes等等都在此定義Task的狀態
.. image:: /Task狀態.png
- Ready : 準備好要執行的狀態
- Running : 正在給CPU執行的狀態
- Block : 等待中的狀態
- Suspended :等待中的狀態
每一種狀態狀態FreeRTOS都會給予一個list儲存（除了runnning)
- Ready list的資料形態
<> >>變數 char類型：以 c 為字首 short類型：以 s 為字首 long類型：以 l 為字首 float類型：以 f 為字首 double類型：以 d 為字首 Enum變數：以 e 為字首 其他（如struct）：以 x 為字首 pointer有一个額外的字首 p , 例如short類型的pointer字首為 ps unsigned類型的變數有一個額外的字首 u , 例如unsigned short類型的變數字首為 us
Functions 文件内：以 prv 為字首 API：以其return類型為字首，按照對變數的定義 名字：以其所在的文件名開頭。如vTaskDelete即在Task.c文件中名稱
- FreeRTOS使用ready list去管理待準備好要執行的tasks而ready list的資料儲存方式如下圖
.. image:: /freertos-figures-full-ready-list-2.png
- Context Switch 時選出下一個欲執行的task
下面是在ready list中依照優先度選取執行目標的程式其中，FreeRTOS的優先度排序最小優先權爲0，數字越大則優先權越高
.. code-block:: c
/* In file: Source/tasks.c */
while( listLIST_IS_EMPTY( &( pxReadyTasksLists[ uxTopReadyPriority ] ) ) )
{
configASSERT( uxTopReadyPriority );
--uxTopReadyPriority;
}
listGET_OWNER_OF_NEXT_ENTRY( pxCurrentTCB, &( pxReadyTasksLists[ uxTopReadyPriority ] ) );
/*In file: Source/include.h */
#define listGET_OWNER_OF_NEXT_ENTRY( pxTCB, pxList )
{
List_t * const pxConstList = ( pxList );
/* Increment the index to the next item and return the item, ensuring */
/* we don't return the marker used at the end of the list. */
( pxConstList )->pxIndex = ( pxConstList )->pxIndex->pxNext;
if( ( void * ) ( pxConstList )->pxIndex == ( void * ) &( ( pxConstList )->xListEnd ) ) \
{
( pxConstList )->pxIndex = ( pxConstList )->pxIndex->pxNext;
}
( pxTCB ) = ( pxConstList )->pxIndex->pvOwner;
}- 創造全新task
TCB的資料結構：
<<<<<<< edited .. code-block:: c ======= .. code-block:: prettyprint
typedef struct tskTaskControlBlock
{
volatile portSTACK_TYPE *pxTopOfStack; /* Points to the location of9aeaf35d3ade38525c0750d6e00adb11b33939a9
typedef struct tskTaskControlBlock
{<<<<<<< edited volatile portSTACK_TYPE pxTopOfStack; / Points to the location of the last item placed on the tasks stack. THIS MUST BE THE FIRST MEMBER OF THE STRUCT. */
xListItem xGenericListItem; /* List item used to place
the TCB in ready and
blocked queues. */
xListItem xEventListItem; /* List item used to place
the TCB in event lists.*/
unsigned portBASE_TYPE uxPriority; /* The priority of the task
where 0 is the lowest
priority. */======= volatile portSTACK_TYPE pxTopOfStack; / Points to the location of the last item placed on the tasks stack. THIS MUST BE THE FIRST MEMBER OF THE STRUCT. */
xListItem xGenericListItem; /* List item used to place
the TCB in ready and
blocked queues. */
xListItem xEventListItem; /* List item used to place
the TCB in event lists.*/
unsigned portBASE_TYPE uxPriority; /* The priority of the task
where 0 is the lowest
priority. */9aeaf35d3ade38525c0750d6e00adb11b33939a9 portSTACK_TYPE pxStack; / Points to the start of the stack. */
signed char pcTaskName[ configMAX_TASK_NAME_LEN ]; /* Descriptive name given
to the task when created.
Facilitates debugging
only. */
#if ( portSTACK_GROWTH > 0 )
portSTACK_TYPE *pxEndOfStack; /* Used for stack overflow
checking on architectures
where the stack grows up
from low memory. */
#endif
#if ( configUSE_MUTEXES == 1 )
unsigned portBASE_TYPE uxBasePriority; /* The priority last
assigned to the task -
used by the priority
inheritance mechanism. */
#endif
} tskTCB;pxTopOfStack , pxEndOfStack :紀錄Stack的大小
uxPriority , uxBasePriority ：紀錄優先權 ,而後者是紀錄原本的優先權（可能發生再Mutux)
xGenericListItem , xEventListItem : 當一個任務被放入到FreeRTOS的一個列表中 ，被插入pointer的地方
xTaskCreate()函數被調用的時候，一個任務被創建。 FreeRTOS為一個任務新分配一個TCB對象，來記錄它的名稱，優先級，和其他細節，接著分配用戶請求的總的堆棧（假設有足夠使用的內存）和在TCB的pxStack成員中記錄堆內存的開始。
而這段程式碼就是ARM Cortex-M4將剛建造好的好的task將暫存器裡的資訊存入stck裡
.. code-block:: c
StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )<<<<<<< edited { /* Simulate the stack frame as it would be created by a context switch interrupt. / ======= { / Simulate the stack frame as it would be created by a context switch interrupt. */ >>>>>>> 9aeaf35d3ade38525c0750d6e00adb11b33939a9
/* Offset added to account for the way the MCU uses the stack on entry/exit
of interrupts, and to ensure alignment. */
pxTopOfStack--;
*pxTopOfStack = portINITIAL_XPSR; /* xPSR */
pxTopOfStack--;
*pxTopOfStack = ( StackType_t ) pxCode; /* PC */
pxTopOfStack--;
*pxTopOfStack = ( StackType_t ) portTASK_RETURN_ADDRESS; /* LR */
/* Save code space by skipping register initialisation. */
pxTopOfStack -= 5; /* R12, R3, R2 and R1. */
*pxTopOfStack = ( StackType_t ) pvParameters; /* R0 */
/* A save method is being used that requires each task to maintain its
own exec return value. */
pxTopOfStack--;
*pxTopOfStack = portINITIAL_EXEC_RETURN;
pxTopOfStack -= 8; /* R11, R10, R9, R8, R7, R6, R5 and R4. */<<<<<<< edited pxTopOfStack; ======= return pxTopOfStack; >>>>>>> 9aeaf35d3ade38525c0750d6e00adb11b33939a9 }
而當ARM Cortex-M4處理器在task遇上中斷時，會將register之內容push上該task的stack的頂端，待下次運行時pop回去 以下是在 port.c裡的實作
.. code-block:: c
<<<<<<< edited void xPortPendSVHandler( void ) { /* This is a naked function. */ __asm volatile ( " mrs r0, psp " " isb " " " " ldr r3, pxCurrentTCBConst " /* Get the location of the current TCB. / " ldr r2, [r3] " " " " tst r14, #0x10 " / Is the task using the FPU context? If so, push high vfp registers. / " it eq " " vstmdbeq r0!, {s16-s31} " " " " stmdb r0!, {r4-r11, r14} " / Save the core registers. / " " " str r0, [r2] " / Save the new top of stack into the first member of the TCB. / " " " stmdb sp!, {r3} " " mov r0, %0 " " msr basepri, r0 " " bl vTaskSwitchContext " " mov r0, #0 " " msr basepri, r0 " " ldmia sp!, {r3} " " " " ldr r1, [r3] " / The first item in pxCurrentTCB is the task top of stack. / " ldr r0, [r1] " " " " ldmia r0!, {r4-r11, r14} " / Pop the core registers. / " " " tst r14, #0x10 " / Is the task using the FPU context? If so, pop the high vfp registers too. / " it eq " " vldmiaeq r0!, {s16-s31} " " " " msr psp, r0 " " isb " " " #ifdef WORKAROUND_PMU_CM001 / XMC4000 specific errata workaround. / #if WORKAROUND_PMU_CM001 == 1 " push { r14 } " " pop { pc } " #endif #endif " " " bx r14 " " " " .align 2 " “pxCurrentTCBConst: .word pxCurrentTCB ” ::“i”(configMAX_SYSCALL_INTERRUPT_PRIORITY) ); } ======= void xPortPendSVHandler( void ) { / This is a naked function. */ __asm volatile ( " mrs r0, psp " " isb " " " " ldr r3, pxCurrentTCBConst " /* Get the location of the current TCB. / " ldr r2, [r3] " " " " tst r14, #0x10 " / Is the task using the FPU context? If so, push high vfp registers. / " it eq " " vstmdbeq r0!, {s16-s31} " " " " stmdb r0!, {r4-r11, r14} " / Save the core registers. / " " " str r0, [r2] " / Save the new top of stack into the first member of the TCB. / " " " stmdb sp!, {r3} " " mov r0, %0 " " msr basepri, r0 " " bl vTaskSwitchContext " " mov r0, #0 " " msr basepri, r0 " " ldmia sp!, {r3} " " " " ldr r1, [r3] " / The first item in pxCurrentTCB is the task top of stack. / " ldr r0, [r1] " " " " ldmia r0!, {r4-r11, r14} " / Pop the core registers. / " " " tst r14, #0x10 " / Is the task using the FPU context? If so, pop the high vfp registers too. / " it eq " " vldmiaeq r0!, {s16-s31} " " " " msr psp, r0 " " isb " " " #ifdef WORKAROUND_PMU_CM001 / XMC4000 specific errata workaround. */ #if WORKAROUND_PMU_CM001 == 1 " push { r14 } " " pop { pc } " #endif #endif " " " bx r14 " " " " .align 2 " “pxCurrentTCBConst: .word pxCurrentTCB ” ::“i”(configMAX_SYSCALL_INTERRUPT_PRIORITY) ); } >>>>>>> 9aeaf35d3ade38525c0750d6e00adb11b33939a9
硬體驅動原理
- 以
GPIO</embedded/GPIO>_ 為例- 參考 STM32Cube_FW_F4_V1.1.0/Projects/STM32F429I-Discovery/Examples/GPIO/GPIO_EXTI/readme.txt 創造全新task TCB的資料結構：
效能表現
●context switch 我們想得知FreeRTOS的context switch時間，並想出一個測試方法：
.. image:: /embedded/test1contextSwitch.jpg 1. 首先創建task1和task2，其中task2的priority大於task1的priority。task2先執行時，馬上就進行vTaskDelay使task2移至block狀態1秒，這時就會發生context switch，換成task1執行，這1秒的時間，task1不斷的進行i++，直到1秒結束後，回到task2執行，再由task2印出i值，並把i重新設0，此為一個週期。此動作可得到i在一秒時可跑至多少，設一秒可跑至k值。
- 設定一個task3其priority高於task2，讓task3執行vTaskDelay 300秒，當300秒結束後，會中斷task1所執行的i++。再由task3印出i值，設其為final_i，k值與final_i值的差額，即為context switch的總時間。
下圖為隨機挑出45個i值做成圖表，其中平均i值為：4280015
.. image:: /embedded/test2contextSwitch.jpg 接著我們測出的final_i值，平均為：3913853，故可得到 (4280015 - 3913853)/ 4280015 = 0.0855 (秒)
0.0855秒代表在300秒的測試內的所有context switch時間之總和
而因為一個週期（第一個步驟）會經過2個context switch（上圖），我們測300內共有600個context switch，故我們測出每個context switch約為：0.0855 / 600 = 142.5（us）
●interrupt latency
我們的架構為是手動設定一個external interrupt，發生在BUTTON_USER按下時，下面程式是我們的實作：
.. code-block:: c
i = 0;
while( STM_EVAL_PBGetState( BUTTON_USER ) ){
i++;
}當BUTTON_USER按下後，會先執行i++直到interruptHandler處理interrupt，讀i值即可得知interrupt latency，而實作結果發現i依舊為0。
●IPC（Inter-Process Communication） throughput
●realtime capability
參考資料
The Architecture of Open Source Applications: FreeRTOS<http://www.aosabook.org/en/freertos.html>_簡體中文翻譯<http://www.ituring.com.cn/article/4063>_
Study of an operating system: FreeRTOS</embedded/FreeRTOS_Melot.pdf>_FreeRTOS 即時核心實用指南</embedded/FreeRTOS-manual-zh.pdf>_
