Lab 8 Department of Computer Science and Information EngineeringNational Taiwan University / 131

Computer System Laboratory

Lab8 – μC/OS

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Lab 8 Department of Computer Science and Information EngineeringNational Taiwan University / 132

Experimental Goal

Practice real-time programming on μC/OS-II.

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Lab 8 Department of Computer Science and Information EngineeringNational Taiwan University / 133

Environment

Host System Windows XP

Build System IAR Embedded Workbench

Target System PTK development board (STM32F207)

Software The source codes of μC/OS-II.

You can find all software on RSWiki CSL Course Software.

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Introduction to μC/OS-II

μC/OS-II is a real-time operating system with the following features: Highly portable

It is written in ANSI C, with target-specific code written in assembly language. It support various platforms, such as x86, MIPS, ARM.

ROMable You can embed μC/OS-II as part of a product with the proper tool chain.

Very scalable Simply specify which features to use through #define constant.

Preemptive real-time It always runs the highest priority task that is ready.

Multitasking It can manage up to 64 tasks, including 8 reserved tasks for μC/OS-II.

The source codes can be downloaded from the official website freely. It is neither freeware nor open source code. You are required to purchase a license for use in any commercial application.

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File Structure in μC/OS-II

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The definition of features in this application

The main kernel

The user tasks

The functionalities of board support package (BSP)

The functions of tick interrupt handler and context switch

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Task Management in μC/OS-II

It is a multitasking and preemptive kernel with a priority-driven real-time scheduling. Nested interrupts could go up to 256 levels. There are 64 priorities, 0 is the highest, and 63 is the lowest.

Each task must have a unique priority in the application. μC/OS-III supports more tasks having the same priority with round-robin

scheduling, while it is not supported in μC/OS-II.

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Non-preemptive kernel Preemptive kernel

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Task Control Blocks

A task control block (TCB) is a data structure used to maintain the state of a task when it is preempted. All valid TCB’s are doubly linked. Free TCB’s are linked in a free list.

The contents of a TCB is saved/restored when a context switch occurs. The stack, priority, time delay, etc. of a task. CPU registers are stored in the stack

rather than in the TCB.

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0OSTCBFreeList OSTCBNext OSTCBNext OSTCBNext OSTCBNext

OSTCBTbl[0] OSTCBTbl[1] OSTCBTbl[2]

OSTCBTbl[OS_MAX_TASKS+OS_N_SYS_TASKS-1]

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Task Scheduler

If there is no user task ready, it will start the idle task (the priority is 63).

In os_core.c:

void OS_Sched (void) {

...

OS_ENTER_CRITICAL();

if (OSIntNesting == 0u) {

if (OSLockNesting == 0u) {

OS_SchedNew();

OSTCBHighRdy = OSTCBPrioTbl[OSPrioHighRdy];

if (OSPrioHighRdy != OSPrioCur) {

#if OS_TASK_PROFILE_EN > 0u

OSTCBHighRdy->OSTCBCtxSwCtr++;

#endif

OSCtxSwCtr++;

OS_TASK_SW();

}

}

}

OS_EXIT_CRITICAL();

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Find the highest ready task.

Perform a context switch.

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A Simple μC/OS-II Code

app.c:

void main(void) {

OSInit();

OSTaskCreate(

((void (*)(void *)) App_TaskStart,

(void *) 0,

(OS_STK *) &App_TaskStartStk[APP_TASK_START_STK_SIZE - 1],

(INT8U) APP_TASK_START_PRIO);

OSStart();

}

void App_TaskStart(void *pdata) {

for (;;) {

/* do something ... */

OSTimeDly(100);

}

}

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Each task performs an infinite loop.

Initialize task ready list, priority table, TCBs, and free pool.

Use OSTaskCreate() or OSTaskCreateExt() to create a task.Tasks become “ready” after they are created.

Start multitasking of μC/OS-II (and never return).

function pointer of a user task

the pointer to the task's top of stack

the task's priority

task-specified data

Use OSTimeDly() or OSTimeDlyHMSM() to do time delay.It allows other tasks to execute.

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Setting up Examples

Step 1: download the PTK_Examples, provided in Lab1.

Step 2: download and extract the μC/OS-II source codes.

Step 3: copy the folder Software in Micrium to PTK_Examples/ePBB/Libraries/OS_uCOS-II/Micrium-V29x.

Step 4: connect the target system STM32F207 to Windows XP.

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Building and Running the UART Example

Step 1: open the serial console. Please set baud rate to 115200bps.

Step 2: open the following workspace in IAR Embedded Workbench IDE. PTK_Examples/ePBB/Applications/Projects/PTK-STM32F207/EWARM-V6/OS_uCOS-II/base_uart/demo.eww

Step 3: compile the project and download the program to the target system.

Step 4: click the button “Go” or press the key “F5” to continue the execution. You will see the message “Hello World!!!” on the serial console.

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Exercise

Now, you are asked to create several tasks in μC/OS-II to complete the followings: Regularly read the value of temperature. Regularly read the value of luminous flux. Set up a key handler to display the message to LCD screen when a key button is

pressed. Other functionalities you can think.

Tips: You need to initialize the LCD device by invoking “ili9325_gui_config()” in the

function “platform_board_init_hook()”. Be careful to the size of stack, do not give it too small!

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Lab Requirement

Show that you can display the information of current temperature and luminous flux on LCD screen by pressing key buttons and your other ideas.

Please hand in your lab report to the FTP. Server: 140.112.90.174 Username: csl2014 Password: csl2014HomeWork Directory: lab8 Please use this format for filename: “G# Ver#”, where G# is your group id and

Ver# is revision version number. E.g., G1 Ver2

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