Micriμm. Getting Started with Micriμm s. Matt Gordon, Sr. Applications Engineer. 9L05I Renesas Electronics America Inc.

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Getting Started with Micriμm s μc/os-iii Kernel

Applications Engineer Micriμm Class ID: 9L05I

2 Matt Gordon Sr. Applications Engineer Responsible for demos and example projects Author of articles and white papers Head of s training program Previous Experience Software engineer at Developed drivers and kernel ports Bachelor s degree in computer engineering from Georgia Tech Renesas Electronics America Inc. All rights reserved.

Renesas Technology & Solution Portfolio 3 2012

4 Agenda Introduction Lab 1 Foreground/Background Systems Kernel-Based Applications Initiating Multitasking Lab 2 Scheduling and Context Switches Lab 3 Additional Kernel Services Lab 4 Conclusion Renesas Electronics America Inc. All rights reserved.

6 Class Objectives Understand what services a real-time kernel provides Learn how to make use of kernel services Learn how kernels are implemented Gain experience with an actual kernel Renesas Electronics America Inc. All rights reserved.

7 Labs Based on µc/os-iii Real-time kernel from Concepts underlying the labs are not µc/os-iii-specific Step-by-step instructions are provided for each lab Renesas Electronics America Inc. All rights reserved.

A µc/os-iii-based Application Application Code s Modules (Portable Code) s Modules

13 Lab 1 Summary The kernel is built alongside application code A kernel-based application looks much like any other C program Application code interacts with the kernel through API functions Renesas Electronics America Inc. All rights reserved.

15 A Foreground/Background Example Background int main (void) { Perform initializations; while (1) { ADC_Read(); SPI_Read(); USB_Packet(); LCD_Update(); Audio_Decode(); File_Write(); } } Foreground void USB_ISR (void) { Clear interrupt; Read packet; } Renesas Electronics America Inc. All rights reserved.

16 Foreground/Background Benefits No upfront cost Minimal training required Developers don t need to learn a kernel s API No need to set aside memory resources to accommodate a kernel There is a small amount of overhead associated with a kernel Renesas Electronics America Inc. All rights reserved.

17 Foreground/Background Drawbacks Difficult to ensure that each operation will meet its deadline All code in the background essentially has the same importance, or priority while (1) { ADC_Read(); SPI_Read(); USB_Packet(); Service other devices; } Potential to delay entire application void ADC_Read (void) { Initialize ADC; while (conv_rdy == 0) { ; } Process converted value; } Renesas Electronics America Inc. All rights reserved.

18 Foreground/Background Drawbacks (Cont.) High-priority code must be placed in the foreground (in an ISR) Lengthy ISRs can negatively impact system responsiveness while (1) { ADC_Read(); SPI_Read(); USB_Packet(); LCD_Update(); Audio_Decode(); File_Write(); } void USB_ISR (void) { Clear interrupt; Read packet; } If a USB packet is received immediately after this function returns, the response time will be lengthy Renesas Electronics America Inc. All rights reserved.

19 Foreground/Background Drawbacks (Cont.) Problems with multiple developers Developers efforts must be closely coordinated Difficult expansion, even with one developer Changes to one portion of the application may negatively impact the remainder of the code Renesas Electronics America Inc. All rights reserved.

21 A Kernel-Based Example Tasks void AppTaskADC (void *p_arg) { while (1) { ADC_Read(); Sleep for 1 ms; } } ISRs void AppISRUSB (void) { Clear interrupt; Signal USB Task; } void AppTaskUSB (void *p_arg) { while (1) { Wait for signal from ISR; USB_Packet(); } } Renesas Electronics America Inc. All rights reserved.

25 Initializing and Starting the Kernel Application code must initialize the kernel µc/os-iii is typically initialized in main() Initialization accomplished through kernel API functions Renesas Electronics America Inc. All rights reserved.

26 OSInit() Must be invoked before any kernel services are used Initializes data structures Creates internal tasks Number of tasks depends on configuration Renesas Electronics America Inc. All rights reserved.

27 µc/os-iii Internal Tasks Always present Optional Idle Task Automatically given lowest priority Tick Task Synchronized with a periodic interrupt Allows µc/os-iii to provide time delays Statistics Task Monitors resource usage ISR Handler Task Facilitates deferred interrupt scheme Timer Task Manages software timers Renesas Electronics America Inc. All rights reserved.

28 Creating a Task void OSTaskCreate (OS_TCB The task s priority CPU_CHAR *p_tcb, *p_name, OS_TASK_PTR p_task, void OS_PRIO CPU_STK CPU_STK *p_arg, prio, *p_stk_base, *p_stk_limit, OS_STK_SIZE stk_size, OS_MSG_QTY OS_TICK void OS_OPT OS_ERR q_size, time_quanta, *p_ext, opt, *p_err); The task itself A pointer to the task s stack Renesas Electronics America Inc. All rights reserved.

30 Stacks Each task has a stack Context is stored on stacks Stack growth conventions vary across platforms Higher memory addresses Lower memory addresses PSW (0x ) PC (p_task) R15 (0x ) R14 (0x ) R13 (0x ) R12 (0x ) R11 (0x ) R10 (0x ) R9 (0x ) R8 (0x ) R7 (0x ) R6 (0x ) R5 (0x ) R4 (0x ) R3 (0x ) R2 (0x ) R1 (p_arg) p_stk Renesas Electronics America Inc. All rights reserved.

33 Lab 2 Summary Application code creates tasks by calling kernel API functions Each task has its own stack A priority must be assigned to each task Renesas Electronics America Inc. All rights reserved.

35 Two Types of Multitasking Scheduling differs from kernel to kernel There are two common approaches to scheduling multiple tasks Cooperative scheduling Preemptive scheduling Renesas Electronics America Inc. All rights reserved.

37 Preemptive Scheduling Interrupt signals the availability of the highpriority task s data ISR The high-priority task is scheduled by the kernel High-Priority Task Low-Priority Task Time Renesas Electronics America Inc. All rights reserved.

39 Scheduling in µc/os-iii µc/os-iii is preemptive Finds highest-priority, ready task Scheduling can be optimized Assembly language, tables Round-robin scheduling is performed only when enabled Renesas Electronics America Inc. All rights reserved.

R11 R12 R13 R14 R15 PSW PC R0 (SP) R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 PSW PC R1 R2 R3 R4 R5 R6 R7

40 Context Switch Switch from Task A to Task B Push Save Update Load Pop registers new stack kernel stack pointer from variables onto pointer stack OSPrioCur OSTCBCurPtr->StkPtr OSTCBCurPtr PSW PC R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 PSW PC R0 (SP) R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 PSW PC R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 Task A s stack Task B s stack Renesas Electronics America Inc. All rights reserved.

41 Interrupts In a preemptive kernel, interrupt handlers are capable of triggering context switches Determine whether a context switch is needed ExampleISR: Save CPU registers; OSIntEnter(); AppISR(); OSIntExit(); Restore CPU registers; Return from interrupt; void AppISR (void) { /* Clear interrupt */ /* Signal task */ } Renesas Electronics America Inc. All rights reserved.

42 The Tick Interrupt Most kernels keep track of time via a periodic interrupt, often called a tick A kernel can use its tick interrupt to implement a number of useful features: Time delays Software timers Timeouts for blocking API functions Renesas Electronics America Inc. All rights reserved.

43 Time Delays void OSTimeDly (OS_TICK dly, OS_OPT opt, OS_ERR *p_err); void OSTimeDlyHMSM (CPU_INT16U hours, CPU_INT16U minutes, CPU_INT16U seconds, CPU_INT32U milli, OS_OPT opt, OS_ERR *p_err); Renesas Electronics America Inc. All rights reserved.

45 Lab 3 Summary Most µc/os-iii ISRs are written at least partially in assembly language ISRs must perform a few kernel-specific operations An interrupt can be set up with a fairly small amount of code Renesas Electronics America Inc. All rights reserved.

48 Synchronization Can be thought of as signaling Tasks can be signaled by ISRs or other tasks While one tasks waits for a signal, the kernel runs other tasks Renesas Electronics America Inc. All rights reserved.

49 Semaphores A means of synchronization Based on a counter Counter value indicates whether or not an event has occurred Two basic operations Pend: wait for event Post: signal occurrence of event Renesas Electronics America Inc. All rights reserved.

50 Semaphore API void OSSemCreate (OS_SEM *p_sem, CPU_CHAR *p_name, OS_SEM_CTR cnt, OS_ERR *p_err); OS_SEM_CTR OSSemPend (OS_SEM *p_sem, OS_TICK timeout, OS_OPT opt, CPU_TS *p_ts, OS_ERR *p_err); OS_SEM_CTR OSSemPost (OS_SEM *p_sem, OS_OPT opt, OS_ERR *p_err); Renesas Electronics America Inc. All rights reserved.

$*p_arg) { Perform initializations; while (1) { Read signals; Calculate statistics; OSSemPost((OS_SEM *)&AppSemDisp, (OS_OPT )OS_OPT_POST_1, (OS_ERR *)&err); Delay for 5 ms; Display } } Task void$

51 Semaphore Example OS_SEM AppSemDisp; /* Initialization Code */ OSSemCreate((OS_SEM *)&AppSemDisp, (CPU_CHAR *) Disp Sem, (OS_SEM_CTR)0, (OS_ERR *)&err); Statistic s Task void AppTaskStat (void *p_arg) { Perform initializations; while (1) { Read signals; Calculate statistics; OSSemPost((OS_SEM *)&AppSemDisp, (OS_OPT )OS_OPT_POST_1, (OS_ERR *)&err); Delay for 5 ms; Display } } Task void AppTaskDisp (void *p_arg) { while (1) { OSSemPend((OS_SEM *)&AppSemDisp, (OS_TICK )100, (OS_OPT )OS_OPT_PEND_BLOCKING, (CPU_TS *)&ts, (OS_ERR *)&err); Update display; } } Renesas Electronics America Inc. All rights reserved.

52 Task Semaphores An alternative to standard semaphores in µc/os-iii Lower overhead Type SemCtr NamePtr TCB SemPendTime OS_SEM PendList SemPendTimeMax Ctr TS Renesas Electronics America Inc. All rights reserved.

54 Event Flag API void OSFlagCreate (OS_FLAG_GRP *p_grp, CPU_CHAR *p_name, OS_FLAGS flags, OS_ERR *p_err); OS_FLAGS OSFlagPend (OS_FLAG_GRP *p_grp, OS_FLAGS flags, OS_TICK timeout, OS_OPT opt, CPU_TS *p_ts, OS_ERR *p_err); OS_FLAGS OSFlagPost (OS_FLAG_GRP *p_grp, OS_FLAGS flags, OS_OPT opt, OS_ERR *p_err); Renesas Electronics America Inc. All rights reserved.

55 Shared Resources Peripheral devices, buffer pools, or simple global variables Accessed by more than one task or by at least one task and one ISR Can cause race conditions Renesas Electronics America Inc. All rights reserved.

56 Shared Resource Example void AppTaskUART (void *p_arg) { Perform initializations; while (1) { Write message to UART; Delay for 1s; } } void AppTaskFS (void *p_arg) { Perform initializations; while (1) { Read file; Write status to UART; } } Renesas Electronics America Inc. All rights reserved.

59 Mutex API void OSMutexCreate (OS_MUTEX *p_mutex, CPU_CHAR *p_name, OS_ERR *p_err); void OSMutexPend (OS_MUTEX *p_mutex, OS_TICK timeout, OS_OPT opt, CPU_TS *p_ts, OS_ERR *p_err); void OSMutexPost (OS_MUTEX *p_mutex, OS_OPT opt, OS_ERR *p_err); Renesas Electronics America Inc. All rights reserved.

$*p_arg) { while (1) { Read Check pressure; for errors; OSMutexPend((OS_MUTEX *)&AppMutexSD, Pressur (OS_TICK )50, e Task (OS_OPT )OS_OPT_PEND_BLOCKING, (CPU_TS *)&ts, (OS_ERR *)&err); Write pressure$

60 Mutex Example OS_MUTEX AppMutexSD; /* Initialization Code */ OSMutexCreate((OS_MUTEX *)&AppMutexSD, (CPU_CHAR *) SDCard Mutex, (OS_ERR *)&err); void AppTaskPressure AppTaskError (void (void *p_arg) *p_arg) { while (1) { Read Check pressure; for errors; OSMutexPend((OS_MUTEX *)&AppMutexSD, Pressur (OS_TICK )50, e Task (OS_OPT )OS_OPT_PEND_BLOCKING, (CPU_TS *)&ts, (OS_ERR *)&err); Write pressure errors to to SD SD card; card; OSMutexPost((OS_MUTEX *)&AppMutexSD, (OS_OPT )OS_OPT_POST_NONE, (OS_ERR *)&err); } } Error Task Renesas Electronics America Inc. All rights reserved.

61 Inter-Task Communication Sending and receiving messages Tasks can send or receive ISRs can send Messages stored in a queue managed by the kernel While one task waits for a message, other tasks run Renesas Electronics America Inc. All rights reserved.

62 Message Queue API void OSQCreate (OS_Q CPU_CHAR OS_MSG_QTY OS_ERR *p_q, *p_name, max_qty, *p_err); void *OSQPend (OS_Q *p_q, OS_TICK timeout, OS_OPT opt, OS_MSG_SIZE *p_msg_size, CPU_TS *p_ts, OS_ERR *p_err); void OSQPost (OS_Q *p_q, void *p_void, OS_MSG_SIZE msg_size, OS_OPT opt, OS_ERR *p_err); Renesas Electronics America Inc. All rights reserved.

63 Message Queue Example OS_Q AppQADC; /* Initialization Code */ OSQCreate((OS_Q *)&AppQADC, (CPU_CHAR *) ADC Queue, (OS_MSG_QTY)20, (OS_ERR *)&err); ADC void AppTaskADC AppISRADC (void) *p_arg) { ISR while Read new (1) value; { Clear adc_val ADC interrupt; = (CPU_INT32U)OSQPend((OS_Q *)&AppQADC, OSQPost((OS_Q *)&AppQADC, (OS_TICK )0, (void *)adc_val, (OS_OPT )OS_OPT_PEND_BLOCKING, (OS_MSG_SIZE)msg_size, (OS_MSG_SIZE *)&msg_size, (OS_OPT )OS_OPT_POST_FIFO, (CPU_TS *)&ts, (OS_ERR *)&err); (OS_ERR *)&err); } Process value; } } ADC Task Renesas Electronics America Inc. All rights reserved.

64 Task Message Queue Message queue included in TCB Less overhead than standard message queue Can be used whenever only one task will be receiving messages Renesas Electronics America Inc. All rights reserved.

65 Additional Services Multi-pend Pend on multiple queues and semaphores Dynamic memory allocation Timers One-shot and periodic software timers with callbacks Renesas Electronics America Inc. All rights reserved.

67 Lab 4 Summary In general, it is desirable to keep interrupt handlers as short as possible Using semaphores, interrupt handlers can signal tasks The two primary semaphore operations are pend and post Renesas Electronics America Inc. All rights reserved.

69 Summary Today we discussed The differences between foreground/background systems and kernel-based applications How a kernel is initialized The contents of a task How a kernel schedules tasks Renesas Electronics America Inc. All rights reserved.

70 Summary (Cont.) Today we discussed What happens during a context switch The structure of ISRs in kernel-based applications Synchronization, mutual exclusion, and inter-task communication services Renesas Electronics America Inc. All rights reserved.

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