1. Computer System Laboratory
Lab4 – μC/OS
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2. Experimental Goal Practice real-time programming on μC/OS-II.
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3. Environment Host System Build System Target System Software Windows XP
IAR Embedded Workbench
Target System
PTK development board (STM32F207)
Software
The source codes of μC/OS-II.
You can find all software on HERE.
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4. 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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5. File Structure in μC/OS-II
The user tasks
The main kernel
The definition of features in this application
The functions of tick interrupt handler and context switch
The functionalities of board support package (BSP)
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6. 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.
Non-preemptive kernel
Preemptive kernel
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7. 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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8. 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();
Find the highest ready task.
Perform a context switch.
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9. 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);
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.
function pointer of a user task
task-specified data
the pointer to the task's top of stack
the task's priority
Start multitasking of μC/OS-II (and never return).
Each task performs an infinite loop.
Use OSTimeDly() or OSTimeDlyHMSM() to do time delay.
It allows other tasks to execute.
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10. Setting up Examples
Step 1: download the PTK_Examples, provided in Lab 3.
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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11. Building and Running the UART Example
Step 1: open the serial console.
Please set baud rate to bps.
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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12. OSTime
A counter recording the number of OS-ticks since the system’s startup.
OS_TICKS_PER_SEC ticks per second. Originally configured to be 1000.
typedef unsigned int INT32U 0~
Other than %d, You may use %u in the format string for printing.
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13. Exercise 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 message to LCD screen when a key button is pressed.
Tips:
You need to initialize the LCD device by invoking “ili9325_gui_config()” in the function “platform_board_init_hook()”.
OSTimeDly(#OS-tick) v.s. VK_DELAY_MS(#ms);
OSTimeDlyHMSM(H, M, S, M)
If confronted by the problem of displaying things on LCD screen, try to adjust the size of stack of a task.
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14. Lab Requirement
Show that you can display the information of current temperature and luminous flux on LCD screen by pressing key buttons.
According to OSTimeDly() and OSTime, calculate the amount of time between each change of temperature (and/or luminous flux) while displaying it on LCD screen.
See how you can make the resolution higher and explain it in the report.
(Hint: you may read the implementation of some functions in os_time.c)
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