ARM PROGRAMMING pot

BÙI QUỐC BẢO 1 ARM PROGRAMMING Bùi Quốc Bảo Why use RTOS •Three sources of LCD messages •Mix of fast and slow hardware •Mix of continuous, periodic, event driven, high priority and low priority requirements BÙI QUỐC BẢO 2 Why use RTOS Concurrent processing BÙI QUỐC BẢO 3 Scheduler  Scheduler là 1 phần của kernel dùng ñể quyết ñịnh tác vụ nào ñược chạy tại mỗi thời ñiểm.  Kernel có thể dừng và phục hồi hoạt ñộng của 1 tác vụ trong khi tác vụ ñang chạy.  Một tác vụ có thể dừng chính nó bằng cách delay (sleep) một khoảng thời gian, hoặc chờ (block) ñể ñợi một sự kiện (vd: keypressed) hay 1 tài nguyên (vd: serialport) Scheduler BÙI QUỐC BẢO 4 Scheduler  At (1) task 1 is executing.  At (2) the kernel suspends task 1  and at (3) resumes task 2.  While task 2 is executing (4), it locks a processor peripheral for it's own exclusive access.  At (5) the kernel suspends task 2  and at (6) resumes task 3. Scheduler  Task 3 tries to access the same processor peripheral, finding it locked, task 3 cannot continue so suspends itself at (7).  At (8) the kernel resumes task 1.  Etc.  The next time task 2 is executing (9) it finishes with the processor peripheral and unlocks it.  The next time task 3 is executing (10) it finds it can now access the  processor peripheral and this time executes until suspended by the kernel. BÙI QUỐC BẢO 5 Realtime scheduler  Mỗi tác vụ phải ñáp ứng (response) trong thời gian qui ñịnh (deadline).  Mỗi tác vụ có 1 mức ưu tiên riêng  Scheduler sẽ ñảm bảo tác vụ có quyền ưu tiên cao luôn ñược thực thi bằng cách tạm dừng tác vụ có quyền ưu tiên thấp. Realtime OS Display Keypad LCD ADC Analog Input filter Sample rate: 5Khz Response time: 0-100ms control output BÙI QUỐC BẢO 6 Keypad handler void vKeyHandlerTask( void *pvParameters ) { // Key handling is a continuous process and as such the task // is implemented using an infinite loop (as most real time // tasks are). for( ;; ) { [Suspend waiting for a key press] [Process the key press] } } control void vControlTask( void *pvParameters ) { for( ;; ) { [Suspend waiting for 0.5ms since the start of the previous cycle] [Sample the input] [Filter the sampled input] [Perform control algorithm] [Output result] } } BÙI QUỐC BẢO 7 Mức ưu tiên  Deadline của tác vụ control thì nghiêm ngặt hơn của tác vụ keypad.  Hậu quả của việc trễ deadline của tác vụ control thì lớn hơn so với keypad BÙI QUỐC BẢO 8 FreeRTOS realtime kernel Example using FreeRTOS int main( void ){ /* Create the 2 task in exactly the same way. */ xTaskCreate( vTask1, "Task 1", 1000, NULL, 1, NULL ); xTaskCreate( vTask2, "Task 2", 1000, NULL, 1, NULL ); /* Start the scheduler so our tasks start executing. */ vTaskStartScheduler(); /* If all is well we will never reach here as the scheduler will now be running. If we do reach here then it is likely that there was insufficient heap available for the idle task to be created. */ for( ;; ); return 0; } BÙI QUỐC BẢO 9 Example using FreeRTOS void vTask1( void *pvParameters ) { const char *pcTaskName = "Task 1 is running\r\n"; volatile unsigned long ul; /* As per most tasks, this task is implemented in an infinite loop. */ for( ;; ) { /* Print out the name of this task. */ vPrintString( pcTaskName ); /* Delay for a period. */ for( ul = 0; ul < mainDELAY_LOOP_COUNT; ul++ ) { } } } Example using FreeRTOS void vTask2( void *pvParameters ) { const char *pcTaskName = "Task 2 is running\r\n"; volatile unsigned long ul; /* As per most tasks, this task is implemented in an infinite loop. */ for( ;; ) { /* Print out the name of this task. */ vPrintString( pcTaskName ); /* Delay for a period. */ for( ul = 0; ul < mainDELAY_LOOP_COUNT; ul++ ) { } } } BÙI QUỐC BẢO 10 The actual execution pattern of the two tasks FreeRTOS source code structure [...]... defined for variables Function names start with the file in which they are defined For example vTaskDelete is defined in Task c x is used both for structures and for RTOS types such as portTickType (in the ARM port this is equivalent to unsigned int) BÙI QU C B O 14 Creating a Task, xTaskCreate portBASE_TYPE xTaskCreate( pdTASK_CODE pvTaskCode, const signed portCHAR * const pcName, unsigned portSHORT usStackDepth, . BÙI QUỐC BẢO 1 ARM PROGRAMMING Bùi Quốc Bảo Why use RTOS •Three sources of LCD messages •Mix of fast and slow hardware •Mix. defined in Task. c  x is used both for structures and for RTOS types such as portTickType (in the ARM port this is equivalent to unsigned int) BÙI QUỐC BẢO 15 Creating a Task, xTaskCreate portBASE_TYPE