uC/OS-II – Real-Time Kernel
Tei-Wei Kuo
ktw@csie.ntu.edu.tw
Dept. of Computer Science and Information Engineering
National Taiwan University
• Slides come from my class notes, slides from graduates and students in my lab (Li-Pin Chang and Shi-Wu Lo), and slides contributed by Labrosse, the author of MicroC/OS-II. All right reserved by CSIE, NTU.
Contents
Introduction
Kernel Structure
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Introduction
Different ports from the official uC/OS-II Web site at http://www.uCOS-II.com.
Neither freeware nor open source code.
uC/OS-II is certified in an avionics product by FAA in July 2000.
Text Book:
Jean J. Labresse, “MicroC/OS-II: The Real-Time Kernel,” CMP Book, ISBN:
1-57820-103-9
Introduction
uC/OS-II
Micro-Controller Operating Systems, Version 2
A very small real-time kernel.
Memory footprint is about 20KB for a fully functional kernel.
Source code is about 5,500 lines, mostly in ANSI C.
It’s source is open but not free for
commercial usages.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Introduction
uC/OS-II
Preemptible priority-driven real-time scheduling.
64 priority levels (max 64 tasks)
8 reserved for uC/OS-II
Each task is an infinite loop.
Deterministic execution times for most uC/OS-II functions and services.
Nested interrupts could go up to 256 levels.
Introduction
uC/OS-II
Supports of various 8-bit to 64-bit platforms: x86, 68x, MIPS, 8051, etc
Easy for development: Borland C++
compiler and DOS (optional).
However, uC/OS-II still lacks of the following features:
Resource synchronization protocols.
Sporadic task support.
Soft-real-time support.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Introduction
Getting started with uC/OS-II!
See how a uC/OS-II program looks like.
Learn how to write a skeleton program for uC/OS-II.
How to initialize uC/OS-II?
How to create real-time tasks?
How to use inter-task
communication mechanisms?
How to catch system events?
Example 1: Multitasking
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Example 1 : Multitasking
13 tasks run concurrently.
2 internal tasks:
The idle task and the statistic task.
11 user tasks:
10 tasks randomly print numbers onto the screen.
Focus: System initialization and task creation.
Example 1: Multitasking
Files
The main program (test.c)
The big include file (includes.h)
The configuration of uC/OS-II (os_cfg.h) for each application
Tools needed:
Borland C++ compiler (V3.1+)
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Example 1
#include "includes.h"
/*
*************************************************************************
********************************
* CONSTANTS
*************************************************************************
********************************
*/
#define TASK_STK_SIZE 512 /* Size of each task's stacks (# of WORDs) */
#define N_TASKS 10 /* Number of identical tasks */
/*
*************************************************************************
********************************
* VARIABLES
*************************************************************************
********************************
*/
OS_STK TaskStk[N_TASKS][TASK_STK_SIZE]; /* Tasks stacks
*/
OS_STK TaskStartStk[TASK_STK_SIZE];
char TaskData[N_TASKS]; /* Parameters to pass to each task */
OS_EVENT *RandomSem;
A semaphore
(explain later)
Main()
void main (void) {
PC_DispClrScr(DISP_FGND_WHITE + DISP_BGND_BLACK);
(1)
OSInit();
(2)
PC_DOSSaveReturn();
(3)
PC_VectSet(uCOS, OSCtxSw);
(4)
RandomSem = OSSemCreate(1);
(5)
OSTaskCreate(TaskStart, (6)
(void *)0,
(void *)&TaskStartStk[TASK_STK_SIZE- 1],
0);
OSStart();
(7)
}
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Main()
OSinit():
internal structures of uC/OS-2.
Task ready list.
Priority table.
Task control blocks (TCB).
Free pool.
Create housekeeping tasks.
The idle task.
The statistics task.
OSinit()
OSTCBStkPtr OSTCBExtPtr = NULL OSTCBStkBottom OSTCBStkSize = stack size OSTCBId = OS_LOWEST_PRIO OSTCBNext OSTCBPrev OSTCBEventPtr = NULL OSTCBMsg = NULL OSTCBDly = 0 OSTCBStat = OS_STAT_RDY OSTCBPrio = OS_LOWEST_PRIO-1 OSTCBX = 6 OSTCBY = 7 OSTCBBitX = 0x40 OSTCBBitY = 0x80 OSTCBDelReq = FALSE
OSTCBStkPtr OSTCBExtPtr = NULL OSTCBStkBottom OSTCBStkSize = stack size OSTCBId = OS_LOWEST_PRIO OSTCBNext OSTCBPrev OSTCBEventPtr = NULL OSTCBMsg = NULL OSTCBDly = 0 OSTCBStat = OS_STAT_RDY OSTCBPrio = OS_LOWEST_PRIO OSTCBX = 7 OSTCBY = 7 OSTCBBitX = 0x80 OSTCBBitY = 0x80 OSTCBDelReq = FALSE
0 0
0 0 0 0 0 0 0 0 0 0
[OS_LOWEST_PRIO]
[OS_LOWEST_PRIO - 1]
[0]
[1]
[2]
[3]
[4]
[5]
[6]
OS_TCB OS_TCB
OSTaskStat() OSTaskIdle() OSTCBPrioTbl[]
OSTCBList OSPrioCur = 0 OSPrioHighRdy = 0 OSTCBCur = NULL OSTCBHighRdy = NULL OSTime = 0L OSIntNesting = 0 OSLockNesting = 0 OSCtxSwCtr = 0 OSTaskCtr = 2 OSRunning = FALSE OSCPUUsage = 0 OSIdleCtrMax = 0L OSIdleCtrRun = 0L OSIdleCtr = 0L
OSStatRdy = FALSE Task Stack Task Stack
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0
OSRdyGrp
OSRdyTbl[]
Ready List
*
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
OSinit()
OSTCBStkPtr OSTCBExtPtr OSTCBStkBottom OSTCBStkSize OSTCBId OSTCBNext OSTCBPrev OSTCBEventPtr OSTCBMsg OSTCBDly OSTCBStat OSTCBPrio OSTCBX OSTCBY OSTCBBitX OSTCBBitY OSTCBDelReq OS_TCB
0 OSTCBFreeList
OS_MAX_TASKS
0 OSEventFreeList
OS_MAX_EVENTS
OS_EVENT OS_EVENT OS_EVENT OS_EVENT
OSQPtr OSQStart OSQEnd OSQIn OSQOut OSQSize OSQEntries OSEventPtr OSEventTbl[]
OSEventCnt OSEventType OSEventGrp
OSTCBStkPtr OSTCBExtPtr OSTCBStkBottom OSTCBStkSize OSTCBId OSTCBNext OSTCBPrev OSTCBEventPtr OSTCBMsg OSTCBDly OSTCBStat OSTCBPrio OSTCBX OSTCBY OSTCBBitX OSTCBBitY OSTCBDelReq OS_TCB
OSTCBStkPtr OSTCBExtPtr OSTCBStkBottom OSTCBStkSize OSTCBId OSTCBNext OSTCBPrev OSTCBEventPtr OSTCBMsg OSTCBDly OSTCBStat OSTCBPrio OSTCBX OSTCBY OSTCBBitX OSTCBBitY OSTCBDelReq OS_TCB
OSEventPtr OSEventTbl[]
OSEventCnt OSEventType OSEventGrp
OSEventPtr OSEventTbl[]
OSEventCnt OSEventType OSEventGrp
OSEventPtr OSEventTbl[]
OSEventCnt OSEventType OSEventGrp OSTCBStkPtr OSTCBExtPtr OSTCBStkBottom OSTCBStkSize OSTCBId OSTCBNext OSTCBPrev OSTCBEventPtr OSTCBMsg OSTCBDly OSTCBStat OSTCBPrio OSTCBX OSTCBY OSTCBBitX OSTCBBitY OSTCBDelReq OS_TCB
0 OSQFreeList
OS_MAX_QS
OS_Q OS_Q OS_Q
OSQPtr OSQStart OSQEnd OSQIn OSQOut OSQSize OSQEntries
OSQPtr OSQStart OSQEnd OSQIn OSQOut OSQSize OSQEntries
OSQPtr OSQStart OSQEnd OSQIn OSQOut OSQSize OSQEntries
OSMemAddr OSMemFreeList OSMemBlkSize OSMemNBlks OSNFree
0 OSMemFreeList
OS_MAX_MEM_PART OS_MEM
OSMemAddr OSMemFreeList OSMemBlkSize OSMemNBlks OSNFree
OS_MEM OS_MEM OS_MEM
OSMemAddr OSMemFreeList OSMemBlkSize OSMemNBlks OSNFree
OSMemAddr OSMemFreeList OSMemBlkSize OSMemNBlks OSNFree
OS_Q
*
Main()
PC_DOSSaveReturn()
Save the current status of DOS for the future restoration.
Interrupt vectors and the RTC tick rate.
Set a global returning point by calling setjump().
uC/OS-II can come back here when it terminates.
PC_DOSReturn()
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
PC_DOSSaveReturn()
void PC_DOSSaveReturn (void) {
PC_ExitFlag = FALSE; (1) OSTickDOSCtr = 8; (2) PC_TickISR = PC_VectGet(VECT_TICK); (3)
OS_ENTER_CRITICAL();
PC_VectSet(VECT_DOS_CHAIN, PC_TickISR); (4) OS_EXIT_CRITICAL();
setjmp(PC_JumpBuf); (5) if (PC_ExitFlag == TRUE) {
OS_ENTER_CRITICAL();
PC_SetTickRate(18); (6) PC_VectSet(VECT_TICK, PC_TickISR); (7) OS_EXIT_CRITICAL();
PC_DispClrScr(DISP_FGND_WHITE + DISP_BGND_BLACK); (8) exit(0); (9) }
} *
Main()
PC_VectSet(uCOS,OSCtxSw)
Install the context switch handler.
Interrupt 0x08 under 80x86 family.
Invoked by INT instruction.
OSStart()
Start multitasking of uC/OS-2.
It never returns to main().
uC/OS-II is terminated if
PC_DOSReturn() is called. *
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Main()
OSSemCreate()
Create a semaphore for resource synchronization.
To protect non-reentrant codes.
The created semaphore becomes a mutual exclusive mechanism if
“1” is given as the initial value.
In this example, a semaphore is created to protect the standard C library “random()”. *
Main()
OSTaskCreate()
Create tasks with the given arguments.
Tasks become “ready” after they are created.
Task
An active entity which could do some computations.
Priority, CPU registers, stack, text, housekeeping status.
The uC/OS-II picks up the highest-priority task to run on context-switching.
Tightly coupled with RTC ISR.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
OSTaskCreate()
OSTaskCreate(
TaskStart,
(void *)0,
&TaskStartStk[TASK_STK_SIZE-1], 0
);
Priority (0=hightest)
Top of Stack Entry point of
the task (a pointer to
function)
User- specified data
TaskStart()
void TaskStart (void *pdata) {
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr;
#endif
char s[100];
INT16S key;
pdata = pdata; /* Prevent compiler warning */
TaskStartDispInit(); /* Initialize the display */
OS_ENTER_CRITICAL();
PC_VectSet(0x08, OSTickISR); /* Install uC/OS-II's clock tick ISR */
PC_SetTickRate(OS_TICKS_PER_SEC); /* Reprogram tick rate */
OS_EXIT_CRITICAL();
OSStatInit(); /* Initialize uC/OS-II's statistics */
TaskStartCreateTasks(); /* Create all the application tasks */
for (;;) {
TaskStartDisp(); /* Update the display */
if (PC_GetKey(&key) == TRUE) { /* See if key has been pressed */
if (key == 0x1B) { /* Yes, see if it's the ESCAPE key */
PC_DOSReturn(); /* Return to DOS */
} }
OSCtxSwCtr = 0; /* Clear context switch counter */
OSTimeDlyHMSM(0, 0, 1, 0); /* Wait one second */
} }
Change the
ticking rate
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
TaskStart()
OS_ENTER_CRITICAL()/OS_EXIT_CRITICAL()
Enable/disable most interrupts.
An alternative way to accomplish mutual exclusion.
No rescheduling is possible during the disabling of interrupts. (different from semaphores)
Processor specific.
CLI/STI (x86 real mode)
Interrupt descriptors (x86 protected mode)
TaskStartCreateTasks()
static void TaskStartCreateTasks (void) {
INT8U i;
for (i = 0; i < N_TASKS; i++) { TaskData[i] = '0' + i;
OSTaskCreate(
Task,
(void *)&TaskData[i],
&TaskStk[i][TASK_STK_SIZE - 1], i + 1);
} }
Priority
Stack
Argument:
character to print Entry point of
the created
task
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Task()
void Task (void *pdata) {
INT8U x;
INT8U y;
INT8U err;
for (;;) {
OSSemPend(RandomSem, 0, &err);/* Acquire semaphore to perform random numbers
*/
x = random(80); /* Find X position where task number will appear
*/
y = random(16); /* Find Y position where task number will appear
*/
OSSemPost(RandomSem); /* Release semaphore
*/
/* Display the task number on the screen
*/
PC_DispChar(x, y + 5, *(char *)pdata, DISP_FGND_BLACK + DISP_BGND_LIGHT_GRAY);
OSTimeDly(1); /* Delay 1 clock tick
*/
} }
Semaphore operations.
Semaphores
A semaphore consists of a wait list and an integer counter.
OSSemPend():
Counter--;
If the value of the semaphore <0, then the task is blocked and moved to the wait list immediately.
A time-out value can be specified.
OSSemPost():
Counter++;
If the value of the semaphore >= 0, then a task in the wait list is removed from the wait list.
Reschedule if needed.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Example 1: Multitasking
Summary:
uC/OS-II is initialized and started by calling OSInit() and OSStart(), respectively.
Before uC/OS-II is started,
The DOS status is saved by calling PC_DOSSaveReturn().
A context switch handler is installed by calling PC_VectSet().
User tasks must be created first!
Shared resources can be protected by semaphores.
OSSemPend(),OSSemPost().
Example 2: Stack Checking
Five tasks do jobs on message sending/receiving, char-displaying with wheel turning, and char-printing.
More task creation options
Better judgment on stack sizes
Stack usage of each task
Different stack sizes for tasks
Emulation of floating point operations
80386 or lower-end CPU’s
Communication through mailbox
Only the pointer is passed.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
The Stack Usage of a Task
.OSTCBStkBottom
.OSTCBStkSize 0
0 0 0
Free Stack Space
Used Stack Space
Initial TOS Deepest Stack Growth
Stack Growth
LOW MEMORY
HIGH MEMORY
CurrentLocation of Stack Pointer
(1) (2)
(3)
(5) (4) (6)
(7)
(8)
Example 2: Stack Checking
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
#define TASK_STK_SIZE 512 /* Size of each task's stacks (# of WORDs)
*/
#define TASK_START_ID 0 /* Application tasks IDs
*/
#define TASK_CLK_ID 1
#define TASK_1_ID 2
#define TASK_2_ID 3
#define TASK_3_ID 4
#define TASK_4_ID 5
#define TASK_5_ID 6
#define TASK_START_PRIO 10 /* Application tasks priorities */ #define TASK_CLK_PRIO 11
#define TASK_1_PRIO 12
#define TASK_2_PRIO 13
#define TASK_3_PRIO 14
#define TASK_4_PRIO 15
#define TASK_5_PRIO 16
OS_STK TaskStartStk[TASK_STK_SIZE]; /* Startup task stack
*/
OS_STK TaskClkStk[TASK_STK_SIZE]; /* Clock task stack
*/
OS_STK Task1Stk[TASK_STK_SIZE]; /* Task #1 task stack
*/
OS_STK Task2Stk[TASK_STK_SIZE]; /* Task #2 task stack
*/
OS_STK Task3Stk[TASK_STK_SIZE]; /* Task #3 task stack
*/
OS_STK Task4Stk[TASK_STK_SIZE]; /* Task #4 task stack
*/
OS_STK Task5Stk[TASK_STK_SIZE]; /* Task #5 task stack
*/
OS_EVENT *AckMbox; /* Message mailboxes for Tasks #4 and #5
*/
OS_EVENT *TxMbox;
2 Mailboxes
void main (void) {
OS_STK *ptos;
OS_STK *pbos;
INT32U size;
PC_DispClrScr(DISP_FGND_WHITE); /* Clear the screen */
OSInit(); /* Initialize uC/OS-II */
PC_DOSSaveReturn(); /* Save environment to return to DOS */
PC_VectSet(uCOS, OSCtxSw); /* Install uC/OS-II's context switch vector */
PC_ElapsedInit(); /* Initialized elapsed time measurement */
ptos = &TaskStartStk[TASK_STK_SIZE - 1]; /* TaskStart() will use Floating- Point */
pbos = &TaskStartStk[0];
size = TASK_STK_SIZE;
OSTaskStkInit_FPE_x86(&ptos, &pbos, &size);
OSTaskCreateExt(TaskStart,
(void *)0, ptos,
TASK_START_PRIO, TASK_START_ID, pbos, size, (void *)0,
OS_TASK_OPT_STK_CHK | OS_TASK_OPT_STK_CLR);
OSStart(); /* Start multitasking */
}
Main()
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
void TaskStart (void *pdata) {
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr;
#endif
INT16S key;
pdata = pdata; /* Prevent compiler warning */
TaskStartDispInit(); /* Setup the display */
OS_ENTER_CRITICAL(); /* Install uC/OS-II's clock tick ISR */
PC_VectSet(0x08, OSTickISR);
PC_SetTickRate(OS_TICKS_PER_SEC); /* Reprogram tick rate */
OS_EXIT_CRITICAL();
OSStatInit(); /* Initialize uC/OS-II's statistics */
AckMbox = OSMboxCreate((void *)0); /* Create 2 message mailboxes */
TxMbox = OSMboxCreate((void *)0);
TaskStartCreateTasks(); /* Create all other tasks */
for (;;) {
TaskStartDisp(); /* Update the display */
if (PC_GetKey(&key)) { /* See if key has been pressed */
if (key == 0x1B) { /* Yes, see if it's the ESCAPE key */
PC_DOSReturn(); /* Yes, return to DOS */
} }
OSCtxSwCtr = 0; /* Clear context switch counter */
OSTimeDly(OS_TICKS_PER_SEC); /* Wait one second */
} }
TaskStart()
Create 2 mailboxes
The dummy loop wait for ‘ESC’
Timer drifting
void Task1 (void *pdata) {
INT8U err;
OS_STK_DATA data; /* Storage for task stack data */
INT16U time; /* Execution time (in uS)
*/
INT8U i;
char s[80];
pdata = pdata;
for (;;) {
for (i = 0; i < 7; i++) { PC_ElapsedStart();
err = OSTaskStkChk(TASK_START_PRIO + i, &data);
time = PC_ElapsedStop();
if (err == OS_NO_ERR) {
sprintf(s, "%4ld %4ld %4ld %6d", data.OSFree + data.OSUsed,
data.OSFree, data.OSUsed, time);
PC_DispStr(19, 12 + i, s, DISP_FGND_BLACK + DISP_BGND_LIGHT_GRAY);
} }
OSTimeDlyHMSM(0, 0, 0, 100); /* Delay for 100 ms */
} }
Task1()
Task1: total 1024 Free 654 Used 370
Extra overheads
on measurement
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
void Task2 (void *data) {
data = data;
for (;;) {
PC_DispChar(70, 15, '|', DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDly(10);
PC_DispChar(70, 15, '/', DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDly(10);
PC_DispChar(70, 15, '-', DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDly(10);
PC_DispChar(70, 15, '\\', DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDly(10);
} }
void Task3 (void *data) {
char dummy[500];
INT16U i;
data = data;
for (i = 0; i < 499; i++) { /* Use up the stack with 'junk'
*/
dummy[i] = '?';
} for (;;) {
PC_DispChar(70, 16, '|', DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDly(20);
PC_DispChar(70, 16, '\\', DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDly(20);
PC_DispChar(70, 16, '-', DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDly(20);
PC_DispChar(70, 16, '/', DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDly(20);
} }
Timer drifting
Task2() & Task3()
void Task4 (void *data) {
char txmsg;
INT8U err;
data = data;
txmsg = 'A';
for (;;) {
OSMboxPost(TxMbox, (void *)&txmsg); /* Send message to Task #5 */
OSMboxPend(AckMbox, 0, &err); /* Wait for acknowledgement from Task #5 */
txmsg++; /* Next message to send */
if (txmsg == 'Z') {
txmsg = 'A'; /* Start new series of messages */
} } }
void Task5 (void *data) {
char *rxmsg;
INT8U err;
data = data;
for (;;) {
rxmsg = (char *)OSMboxPend(TxMbox, 0, &err); /* Wait for message from Task #4 */
PC_DispChar(70, 18, *rxmsg, DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDlyHMSM(0, 0, 1, 0); /* Wait 1 second */
OSMboxPost(AckMbox, (void *)1); /* Acknowledge reception of msg */
} }
Task4() and Task5()
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Mail Box
A mailbox is for data exchanging between tasks.
A mailbox consists of a data pointer and a wait-list.
OSMboxPend():
The message in the mailbox is retrieved.
If the mailbox is empty, the task is immediately blocked and moved to the wait-list.
A time-out value can be specified.
OSMboxPost():
A message is posted in the mailbox.
If there is already a message in the mailbox, then an error is returned (not overwritten).
If tasks are waiting for a message from the mailbox, then the task with the highest priority is removed from the wait-list and scheduled to run.
OSTaskStkInit_FPE_x86()
OSTaskStkInit_FPE_x86(&ptos, &pbos,
&size)
Pass the original top address, the
original bottom address, and the size of the stack.
On the return, arguments are modified,
and some stack space are reserved for
the floating point library.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
OSCreateTaskExt()
OSTaskCreateExt(
TaskStart, (void *)0, ptos,
TASK_START_PRIO, TASK_START_ID, pbos,
size,
(void *)0,
OS_TASK_OPT_STK_CHK | OS_TASK_OPT_STK_CLR );
OSTaskStkCheck()
Check for any stack overflow
bos < (tos – stack length)
Local variables, arguments for procedure calls, and temporary storage for ISR’s.
uC/OS-II can check for any stack overflow for the creation of tasks and when OSTaskStkCheck() is called.
uC/OS-II does not automatically
check for the status of stacks.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Example2: Stack Checking
Summary:
Local variable, function calls, and ISR’s will utilize the stack space of user tasks.
ISR will use the stack of the interrupted task.
If floating-point operations are needed, then some stack space should be reserved.
Mailboxes can be used to synchronize the work of tasks.
Example 3: Extension of uC/OS-II
A Pointer to from the TCB of each task to a user-provided data structure
Passing user-specified data structures on task creations or have application-specific usage.
Message queues
More than one potiners
Demonstration on how to use OS hooks to
receive/process desired event from the uC/OS-
II
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Example 3: Extension of uC/OS-II
#define TASK_STK_SIZE 512 /* Size of each task's stacks (# of WORDs) */
#define TASK_START_ID 0 /* Application tasks */
#define TASK_CLK_ID 1
#define TASK_1_ID 2
#define TASK_2_ID 3
#define TASK_3_ID 4
#define TASK_4_ID 5
#define TASK_5_ID 6
#define TASK_START_PRIO 10 /* Application tasks priorities */
#define TASK_CLK_PRIO 11
#define TASK_1_PRIO 12
#define TASK_2_PRIO 13
#define TASK_3_PRIO 14
#define TASK_4_PRIO 15
#define TASK_5_PRIO 16
#define MSG_QUEUE_SIZE 20 /* Size of message queue used in example */
typedef struct { char TaskName[30];
INT16U TaskCtr;
INT16U TaskExecTime;
INT32U TaskTotExecTime;
} TASK_USER_DATA;
OS_STK TaskStartStk[TASK_STK_SIZE]; /* Startup task stack */
OS_STK TaskClkStk[TASK_STK_SIZE]; /* Clock task stack */
OS_STK Task1Stk[TASK_STK_SIZE]; /* Task #1 task stack */
OS_STK Task2Stk[TASK_STK_SIZE]; /* Task #2 task stack */
OS_STK Task3Stk[TASK_STK_SIZE]; /* Task #3 task stack */
OS_STK Task4Stk[TASK_STK_SIZE]; /* Task #4 task stack */
OS_STK Task5Stk[TASK_STK_SIZE]; /* Task #5 task stack */
TASK_USER_DATA TaskUserData[7];
OS_EVENT *MsgQueue; /* Message queue pointer */
void *MsgQueueTbl[20]; /* Storage for messages */
Message queue and an array of event
User-defined data
structure to pass to tasks
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
void Task1 (void *pdata) {
char *msg;
INT8U err;
pdata = pdata;
for (;;) {
msg = (char *)OSQPend(MsgQueue, 0, &err);
PC_DispStr(70, 13, msg, DISP_FGND_YELLOW + DISP_BGND_BLUE);
OSTimeDlyHMSM(0, 0, 0, 100);
} }
void Task2 (void *pdata) {
char msg[20];
pdata = pdata;
strcpy(&msg[0], "Task 2");
for (;;) {
OSQPost(MsgQueue, (void *)&msg[0]);
OSTimeDlyHMSM(0, 0, 0, 500);
} }
Task 2, 3, 4 are functionally
identical.
Message Queues
A message queue consists of an array of elements and a wait-list.
Different from a mailbox, a message queue can hold many data elements (in a FIFO basis).
As same as mailboxes, there can be multiple tasks pend/post to a message queue.
OSQPost(): a message is appended to the queue. The highest-priority pending task (in the wait-list) receives the message and is scheduled to run, if any.
OSQPend(): a message is removed from the
array of elements. If no message can be
retrieved, the task is moved to the wait-list and
becomes blocked.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
A hook function will be called by uC/OS-II when the corresponding event occurs.
Event handlers could be in user programs.
For example, OSTaskSwHook () is called every time when context switch occurs.
The hooks are specified in the compiling time in uC/OS-II:
uC/OS-II is an embedded OS.
OS_CFG.H (OS_CPU_HOOKS_EN = 0)
Many OS’s can register and un-register hooks.
Hooks
void OSInitHookBegin (void) void OSInitHookEnd (void)
void OSTaskCreateHook (OS_TCB *ptcb) void OSTaskDelHook (OS_TCB *ptcb) void OSTaskIdleHook (void)
void OSTaskStatHook (void) void OSTaskSwHook (void)
void OSTCBInitHook (OS_TCB *ptcb) void OSTimeTickHook (void)
User Customizable Hooks for
uC/OS-II
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
void OSTaskStatHook (void) {
char s[80];
INT8U i;
INT32U total;
INT8U pct;
total = 0L; /* Totalize TOT. EXEC. TIME for each task */
for (i = 0; i < 7; i++) {
total += TaskUserData[i].TaskTotExecTime;
DispTaskStat(i); /* Display task data */
}
if (total > 0) {
for (i = 0; i < 7; i++) { /* Derive percentage of each task */
pct = 100 * TaskUserData[i].TaskTotExecTime / total;
sprintf(s, "%3d %%", pct);
PC_DispStr(62, i + 11, s, DISP_FGND_BLACK + DISP_BGND_LIGHT_GRAY);
} }
if (total > 1000000000L) { /* Reset total time counters at 1 billion */
for (i = 0; i < 7; i++) {
TaskUserData[i].TaskTotExecTime = 0L;
} } }
void OSTaskSwHook (void) {
INT16U time;
TASK_USER_DATA *puser;
time = PC_ElapsedStop(); /* This task is done */
PC_ElapsedStart(); /* Start for next task */
puser = OSTCBCur->OSTCBExtPtr; /* Point to used data */
if (puser != (TASK_USER_DATA *)0) {
puser->TaskCtr++; /* Increment task counter */
puser->TaskExecTime = time; /* Update the task's execution time */
puser->TaskTotExecTime += time; /* Update the task's total execution time */
} }
OSTCBCur ÆTCB of the current task OSTCBHighRdyÆTC
B of the new task Elapsed
time for the current task
Example 3: Extension of uC/OS-II
Summary:
Message queues can be used to synchronize among tasks.
Multiple messages can be held in a queue.
Multiple tasks can “pend”/“post” to message queues simultaneously.
Hooks can be used to do some user- specific computations on certain OS events occurs.
They are specified in the compiling time.
A Pointer to from the TCB of each task to a
user-provided data structure
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Introduction
Getting Started with uC/OS-II:
How to write a dummy uC/OS-II program?
How the control flows among procedures?
How tasks are created?
How tasks are synchronized by semaphore, mailbox, and message queues?
How the space of a stack is utilized?
How to capture system events?
Contents
Introduction
Kernel Structure
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Objectives
To understand what a task is.
To learn how uC/OS-II manages tasks.
To know how an interrupt service routine (ISR) works.
To learn how to determine the percentage of CPU that your application is using.
The uC/OS-II File Structure
Application Code (Your Code!) Processor independent
implementations
•Scheduling policy
•Event flags
•Semaphores
•Mailboxes
•Event queues
•Task management
•Time management
•Memory management
Application Specific Configurations
OS_CFG.H
• Max # of tasks
• Max Queue length
•…
uC/OS-2 port for processor specific codes
CPU Timer
Hardware
Software
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Source Availability
Download the “Ports” of uC/OS-II from the web site http://www.ucos- II.com/
Processor-independent and
dependent code sections (for Intel 80x86) are contained in the
companion CD-ROM of the textbook
Critical Sections
A critical section is a portion of code that is not safe from race conditions b ecause of the use of shared resources.
They can be protected by interrupt
disabling/enabling interrupts or semaphores.
The use of semaphores often imposes a more significant amount of overheads.
A RTOS often use interrupts disabling/
enabling to protect critical sections.
Once interrupts are disabled, neither
context switches nor any other ISR’s can
occur.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Critical Sections
Interrupt latency is vital to an RTOS!
Interrupts should be disabled as short as possible to improve the responsiveness.
It must be accounted as a blocking time in the
schedulability analysis.
Interrupt disabling must be used carefully:
E.g., if OSTimeDly() is called with interrupt disabled, the machine might hang!
...
OS_ENTER_CRITICAL();
/* Critical Section */
OS_EXIT_CRITICAL();
...
Critical Sections
The states of the processor must be carefully maintained across multiple calls of
OS_ENTER_CRITICAL() and OS_EXIT_CRITICAL().
There are three implementations in uC/OS-II:
Interrupt enabling/disabling instructions.
Interrupt status save/restore onto/from stacks.
Processor Status Word (PSW) save/restore onto/from memory variables.
Interrupt enabling/disabling can be done by various way:
In-line assembly.
Compiler extension for specific processors.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Critical Sections
OS_CRITICAL_METHOD=1
Interrupt enabling/disabling instructions.
The simplest way! However, this approach does not have the sense of “save” and
“restore”.
Interrupt statuses might not be consistent across kernel services/function calls!!
{ .
disable_interrupt();
a_kernel_service();
. . }
{ .
disable_interrupt();
critical section enable_interrupt();
. }
Interrupts are now implicitly re-enabled!
Critical Sections
OS_CRITICAL_METHOD=2
Processor Status Word (PSW) can be saved/restored onto/from stacks.
PSW’s of nested interrupt enable/disable operations can be exactly recorded in stacks.
#define OS_ENTER_CRITICAL() \ asm(“PUSH PSW”) \ asm(“DI”)
#define OS_EXIT_CRITICAL() \ asm(“POP PSW”)
Some compilers might not be smart enough to adjust the stack pointer after the processing of
in-line assembly.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Critical Sections
OS_CRITICAL_METHOD=3
The compiler and processor allow the PSW to be saved/restored to/from a memory variable.
void foo(arguments) {
OS_CPU_SR cpu_sr;
.
cpu_sr = get_processor_psw();
disable_interrupts();
.
/* critical section */
.
set_processor_psw(cpu_sr);
. }
OS_ENTER_CRITICAL()
OS_EXIT_CRITICAL()
Tasks
A task is an active entity which could do some computations.
Under real-time uC/OS-II systems, a task is typically an infinite loop.
void YourTask (void *pdata) (1) {
for (;;) { (2) /* USER CODE */
Call one of uC/OS-II’s services:
OSMboxPend();
OSQPend();
OSSemPend();
OSTaskDel(OS_PRIO_SELF);
OSTaskSuspend(OS_PRIO_SELF);
OSTimeDly();
OSTimeDlyHMSM();
/* USER CODE */
} }
Delay itself for the next event/period, so that other tasks
can run.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Tasks
uC/OS-II can have up to 64 priorities.
Each task must be associated with an unique priority.
63 and 62 are reserved (idle, stat).
An insufficient number of priority might damage the schedulability of a real-time scheduler.
The number of schedulable task would be reduced.
Because there is no distinction among the tasks with the same priority.
For example, under RMS, tasks have different periods but are assigned with the same priority.
It is possible that all other tasks with the same priority are always issued before a particular task.
Fortunately, most embedded systems have a limited number of tasks to run.
Tasks
A task is created by OSTaskCreate() or OSTaskCreateExt().
The priority of a task can be changed by OSTaskChangePrio().
A task could delete itself when it is done.
void YourTask (void *pdata) { /* USER CODE */
OSTaskDel(OS_PRIO_SELF);
} The priority of
the current task
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Task States
Dormant: Procedures residing on RAM/ROM is not an task unless you call OSTaskCreate() to execute them.
No tasks correspond to the codes yet!
Ready: A task is neither delayed nor waiting for any event to occur.
A task is ready once it is created.
Running: A ready task is scheduled to run on the CPU .
There must be only one running task.
The task running might be preempted and become ready.
Waiting: A task is waiting for certain events to occur.
Timer expiration, signaling of semaphores, messages in mailboxes, and etc.
ISR: A task is preempted by an interrupt.
The stack of the interrupted task is utilized by the ISR.
Task States
RUNNING READY
OSTaskCreate() OSTaskCreateExt()
Task is Preempted OSMBoxPend() OSQPend() OSSemPend() OSTaskSuspend() OSTimeDly() OSTimeDlyHMSM() OSMBoxPost()
OSQPost() OSQPostFront() OSSemPost() OSTaskResume() OSTimeDlyResume() OSTimeTick()
OSTaskDel()
DORMANT
WAITING
OSStart() OSIntExit() OS_TASK_SW()
OSTaskDel() OSTaskDel()
Interrupt
OSIntExit()
ISR
OSintExit()
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Task States
A task can delay itself by calling OSTimeDly() or OSTimeDlyHMSM().
The task is placed in the waiting state.
The task will be made ready by the execution of OSTimeTick().
It is the clock ISR! You don’t have to call it explicitly from your code.
A task can wait for an event by OSFlagPend(), OSSemPend(), OSMboxPend(), or OSQPend().
The task remains waiting until the occurrence of the desired event (or timeout).
Task States
The running task could be preempted by an ISR unless interrupts are
disabled.
ISR’s could make one or more tasks ready by signaling events.
On the return of an ISR, the scheduler will check if rescheduling is needed.
Once new tasks become ready, the next highest priority ready task is scheduled to run (due to occurrences of events, e.g., timer expiration).
If no task is running, and all tasks are
not in the ready state, the idle task
executes.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Task Control Blocks (TCB)
A TCB is a main-memory-resident data structure used to maintain the state of a task, especially when it is preempted.
Each task is associated with a TCB.
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.
Task priority, delay counter, event to wait, the location of the stack.
CPU registers are stored in the stack rather than in the TCB.
typedef struct os_tcb {
OS_STK *OSTCBStkPtr;
#if OS_TASK_CREATE_EXT_EN void *OSTCBExtPtr;
OS_STK *OSTCBStkBottom;
INT32U OSTCBStkSize;
INT16U OSTCBOpt;
INT16U OSTCBId;
#endif
struct os_tcb *OSTCBNext;
struct os_tcb *OSTCBPrev;
#if (OS_Q_EN && (OS_MAX_QS >= 2)) || OS_MBOX_EN || OS_SEM_EN OS_EVENT *OSTCBEventPtr;
#endif
#if (OS_Q_EN && (OS_MAX_QS >= 2)) || OS_MBOX_EN void *OSTCBMsg;
#endif
INT16U OSTCBDly;
INT8U OSTCBStat;
INT8U OSTCBPrio;
INT8U OSTCBX;
INT8U OSTCBY;
INT8U OSTCBBitX;
INT8U OSTCBBitY;
#if OS_TASK_DEL_EN
BOOLEAN OSTCBDelReq;
#endif
} OS_TCB;
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Task Control Blocks (TCB)
.OSTCBStkPtr contains a pointer to the current TOS for the task.
It is the first entry of TCB so that it can be accessed directly from assembly
language. (offset=0)
.OSTCBExtPtr is a pointer to a user- definable task control block extension.
Set OS_TASK_CREATE_EXT_EN to 1.
The pointer is set when OSTaskCreateExt( ) is called
The pointer is ordinarily cleared in the hook OSTaskDelHook().
Task Control Blocks (TCB)
.OSTCBStkBottom is a pointer to the bottom of the task’s stack.
.OSTCBStkSize holds the size of the stack in the number of elements, instead of bytes.
The element size is a macro OS_STK.
The total stack size is
OSTCBStkSize*OS_STK bytes
.OSTCBStkBottom and .OSTCBStkSize are used to check up stacks (if
OSTaskCreateExt( ) is invoked).
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Task Control Blocks (TCB)
Space in use
Top of Stack (TOS)
Stack growi ng direction
Free Space
Bottom of Stack (BOS)
Current TOS, points to the newest element.
Task Control Blocks (TCB)
.OSTCBOpt holds “options” that can be passed to OSTaskCreateExt( )
OS_TASK_OPT_STK_CHK: stack checking is enabled for the task .
OS_TASK_OPT_STK_CLR: indicates that the stack needs to be cleared when the task is created.
OS_TASK_OPT_SAVE_FP: Tell OSTaskCreateExt() that the task will be doing floating-point computations.
Floating point processor’s registers must be saved to the stack on context-switches.
.OSTCBId: hold an identifier for the task.
.OSTCBNext and .OSTCBPrev are used to doubly
link OS_TCB’s
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Task Control Blocks (TCB)
.OSTCBEVEventPtr is pointer to an event control block.
.OSTCBMsg is a pointer to a message that is sent to a task.
.OSTCBFlagNode is a pointer to a flagnode.
.OSTCBFlagsRdy maintains info regarding which event flags make the task ready .
.OSTCBDly is used when
a task needs to be delayed for a certain number of clock ticks, or
a task needs to wait for an event to occur with a timeout.
.OSTCBStat contains the state of the task (0 is ready to run).
.OSTCBPrio contains the task priority.
Task Control Blocks (TCB)
.OSTCBX .OSTCBY .OSTCBBitX and .OSTCBBitY
They are used to accelerate the process of making a task ready to run or make a task wait for an event.
.OSTCBDelReq is a boolean used to indicate whether or not a task requests that the current task to be deleted.
OS_MAX_TASKS is specified in OS_CFG.H
# OS_TCB’s allocated by uC/OS-II
OSTCBTbl[ ] : where all OS_TCB’s are placed.
When uC/OS-II is initialized, all OS_TCB’s in the table are linked in a singly linked list of free OS_TCB’s.
OSTCBY = priority >> 3;
OSTCBBitY = OSMapTbl[priority >> 3];
OSTCBX = priority & 0x07;
OSTCBBitX = OSMapTbl[priority & 0x07];
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
Task Control Blocks (TCB)
When a task is created, the OS_TCB pointed to by OSTCBFreeList is assigned to the task, and OSTCBFreeList is adjusted to point to the next OS_TCB in the chain.
When a task is deleted, its OS_TCB is returned to the list of free OS_TCB.
An OS_TCB is initialized by the function OS_TCBInit(), which is called by
OSTaskCreate().
0 OSTCBFreeList OSTCBNext OSTCBNext OSTCBNext OSTCBNext
OSTCBTbl[0] OSTCBTbl[1] OSTCBTbl[2]
OSTCBTbl[OS_MAX_TASKS+OS_N_SYS_TASKS-1]
INT8U OS_TCBInit (INT8U prio, OS_STK *ptos, OS_STK *pbos, INT16U id, INT32U stk_size, void *pext, INT16U opt)
{
#if OS_CRITICAL_METHOD == 3 /* Allocate storage for CPU status register */
OS_CPU_SR cpu_sr;
#endif
OS_TCB *ptcb;
OS_ENTER_CRITICAL();
ptcb = OSTCBFreeList; /* Get a free TCB from the free TCB list */
if (ptcb != (OS_TCB *)0) {
OSTCBFreeList = ptcb->OSTCBNext; /* Update pointer to free TCB list */
OS_EXIT_CRITICAL();
ptcb->OSTCBStkPtr = ptos; /* Load Stack pointer in TCB */
ptcb->OSTCBPrio = (INT8U)prio; /* Load task priority into TCB */
ptcb->OSTCBStat = OS_STAT_RDY; /* Task is ready to run */
ptcb->OSTCBDly = 0; /* Task is not delayed */
#if OS_TASK_CREATE_EXT_EN > 0
ptcb->OSTCBExtPtr = pext; /* Store pointer to TCB extension */
ptcb->OSTCBStkSize = stk_size; /* Store stack size */
ptcb->OSTCBStkBottom = pbos; /* Store pointer to bottom of stack */
ptcb->OSTCBOpt = opt; /* Store task options */
ptcb->OSTCBId = id; /* Store task ID */
#else
pext = pext; /* Prevent compiler warning if not used */
stk_size = stk_size;
pbos = pbos;
opt = opt;
id = id;
#endif
#if OS_TASK_DEL_EN > 0
ptcb->OSTCBDelReq = OS_NO_ERR;
#endif
ptcb->OSTCBY = prio >> 3; /* Pre-compute X, Y, BitX and BitY */
ptcb->OSTCBBitY = OSMapTbl[ptcb->OSTCBY];
ptcb->OSTCBX = prio & 0x07;
ptcb->OSTCBBitX = OSMapTbl[ptcb->OSTCBX];
Get a free TCB from
the free list
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
#if OS_EVENT_EN > 0
ptcb->OSTCBEventPtr = (OS_EVENT *)0; /* Task is not pending on an event */
#endif
#if (OS_VERSION >= 251) && (OS_FLAG_EN > 0) && (OS_MAX_FLAGS > 0) && (OS_TASK_DEL_EN > 0)
ptcb->OSTCBFlagNode = (OS_FLAG_NODE *)0; /* Task is not pending on an event flag */
#endif
#if (OS_MBOX_EN > 0) || ((OS_Q_EN > 0) && (OS_MAX_QS > 0))
ptcb->OSTCBMsg = (void *)0; /* No message received */
#endif
#if OS_VERSION >= 204 OSTCBInitHook(ptcb);
#endif
OSTaskCreateHook(ptcb); /* Call user defined hook */
OS_ENTER_CRITICAL();
OSTCBPrioTbl[prio] = ptcb;
ptcb->OSTCBNext = OSTCBList; /* Link into TCB chain */
ptcb->OSTCBPrev = (OS_TCB *)0;
if (OSTCBList != (OS_TCB *)0) { OSTCBList->OSTCBPrev = ptcb;
}
OSTCBList = ptcb;
OSRdyGrp |= ptcb->OSTCBBitY; /* Make task ready to run */
OSRdyTbl[ptcb->OSTCBY] |= ptcb->OSTCBBitX;
OS_EXIT_CRITICAL();
return (OS_NO_ERR);
}
OS_EXIT_CRITICAL();
return (OS_NO_MORE_TCB);
}
User-defined hook is called here.
Priority table TCB list
Ready list
Ready List
Ready list is a special bitmap to reflect which task is currently in the ready state.
Each task is identified by its unique priority in the bitmap.
A primary design consideration of the ready list is how to efficiently locate the highest-priority ready task.
The designer could trade some ROM space for an improved performance.
If a linear list is adopted, it takes O(n) to locate the highest-priority ready task.
It takes O(log n) if a heap is adopted.
Under the design of ready list of uC/OS-II, it takes only O(1).
Note that the space consumption is much more than other
approaches, and it also depends on the bus width.
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
OSTCBStkPtr OSTCBExtPtr = NULL OSTCBStkBottom OSTCBStkSize = stack size OSTCBId = OS_LOWEST_PRIO OSTCBNext OSTCBPrev OSTCBEventPtr = NULL OSTCBMsg = NULL OSTCBDly = 0 OSTCBStat = OS_STAT_RDY OSTCBPrio = OS_LOWEST_PRIO-1 OSTCBX = 6 OSTCBY = 7 OSTCBBitX = 0x40 OSTCBBitY = 0x80 OSTCBDelReq = FALSE
OSTCBStkPtr OSTCBExtPtr = NULL OSTCBStkBottom OSTCBStkSize = stack size OSTCBId = OS_LOWEST_PRIO OSTCBNext OSTCBPrev OSTCBEventPtr = NULL OSTCBMsg = NULL OSTCBDly = 0 OSTCBStat = OS_STAT_RDY OSTCBPrio = OS_LOWEST_PRIO OSTCBX = 7 OSTCBY = 7 OSTCBBitX = 0x80 OSTCBBitY = 0x80 OSTCBDelReq = FALSE
0 0
0 0 0 0 0 0 0 0 0 0
[OS_LOWEST_PRIO]
[OS_LOWEST_PRIO - 1]
[0]
[1]
[2]
[3]
[4]
[5]
[6]
OS_TCB OS_TCB
OSTaskStat() OSTaskIdle() OSTCBPrioTbl[]
OSTCBList OSPrioCur = 0 OSPrioHighRdy = 0 OSTCBCur = NULL OSTCBHighRdy = NULL OSTime = 0L OSIntNesting = 0 OSLockNesting = 0 OSCtxSwCtr = 0 OSTaskCtr = 2 OSRunning = FALSE OSCPUUsage = 0 OSIdleCtrMax = 0L OSIdleCtrRun = 0L OSIdleCtr = 0L
OSStatRdy = FALSE Task Stack Task Stack 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0
OSRdyGrp
OSRdyTbl[]
Ready List
0 1 2 3 4 5 6 7
8 9 10 11 12 13 14 15
16 17 18 19 20 21 22 23
24 25 26 27 28 29 30 31
32 33 34 35 36 37 38 39
40 41 42 43 44 45 46 47
48 49 50 51 52 53 54 55
56 57 58 59 60 61 62 63
Task Priority # Lowest Priority Task (Idle Task)
Highest Priority Task
X
Y OSRdyTbl[OS_LOWEST_PRIO / 8 + 1]
0 1 2 3 4 5 6 7
OSRdyGrp
[7]
[6]
[5]
[4]
[3]
[2]
[1]
[0]
0 0 Y Y Y X X X
Bit position in OSRdyTbl[OS_LOWEST_PRIO / 8 + 1]
Bit position in OSRdyGrp and
Index into OSRdyTbl[OS_LOWEST_PRIO / 8 + 1]
Task's Priority
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
10000000 7
01000000 6
00100000 5
00010000 4
00001000 3
00000100 2
00000010 1
00000001 0
Bit mask (Binary) Index
Bit 0 in OSRdyGrp is 1 when any bit in OSRdyTbl[0] is 1.
Bit 1 in OSRdyGrp is 1 when any bit in OSRdyTbl[1] is 1.
Bit 2 in OSRdyGrp is 1 when any bit in OSRdyTbl[2] is 1.
Bit 3 in OSRdyGrp is 1 when any bit in OSRdyTbl[3] is 1.
Bit 4 in OSRdyGrp is 1 when any bit in OSRdyTbl[4] is 1.
Bit 5 in OSRdyGrp is 1 when any bit in OSRdyTbl[5] is 1.
Bit 6 in OSRdyGrp is 1 when any bit in OSRdyTbl[6] is 1.
Bit 7 in OSRdyGrp is 1 when any bit in OSRdyTbl[7] is 1.
OSRdyGrp |= OSMapTbl[prio >> 3];
OSRdyTbl[prio >> 3] |= OSMapTbl[prio & 0x07];
if ((OSRdyTbl[prio >> 3] &= ~OSMapTbl[prio & 0x07]) == 0) OSRdyGrp &= ~OSMapTbl[prio >> 3];
• Make a task ready to run:
• Remove a task from the ready list:
OSMapTbl
What does this code do?
char x,y,mask;
x = prio & 0x07;
y = prio >> 3;
mask = ~(OSMapTbl[x]); // a mask for bit clearing if((OSRdyTbl[x] &= mask) == 0)// clear the task’s bit { // the group bit should be cleared too
mask = ~(OSMapTbl[y]); // another bit mask…
OSRdyGrp &= mask; // clear the group bit }
if ((OSRdyTbl[prio >> 3] &= ~OSMapTbl[prio & 0x07]) == 0) OSRdyGrp &= ~OSMapTbl[prio >> 3];
Coding Style
How about this:
The author writes:
* All rights reserved, Tei-Wei Kuo, National Taiwan University, 2003.
mov al,byte ptr [bp-17]
mov ah,0
and ax,7
lea dx,word ptr [bp-8]
add ax,dx
mov bx,ax
mov al,byte ptr ss:[bx]
not al
mov dl,byte ptr [bp-17]
mov dh,0
sar dx,3
lea bx,word ptr [bp-16]
add dx,bx
mov bx,dx
and byte ptr ss:[bx],al
mov al,byte ptr ss:[bx]
or al,al
jne short @1@86
mov al,byte ptr [bp-17]
mov ah,0
sar ax,3
lea dx,word ptr [bp-8]
add ax,dx
mov bx,ax
mov al,byte ptr ss:[bx]
not al
and byte ptr [bp-18],al
mov al,byte ptr [bp-17]
and al,7
mov byte ptr [bp-19],al
mov al,byte ptr [bp-17]
mov ah,0
sar ax,3
mov byte ptr [bp-20],al
mov al,byte ptr [bp-19]
mov ah,0
lea dx,word ptr [bp-8]
add ax,dx
mov bx,ax
mov al,byte ptr ss:[bx]
not al
mov cl,al
mov al,byte ptr [bp-19]
mov ah,0
lea dx,word ptr [bp-16]
add ax,dx
mov bx,ax
and byte ptr ss:[bx],cl
mov al,byte ptr ss:[bx]
or al,al
jne short @1@142
mov al,byte ptr [bp-20]
mov ah,0
lea dx,word ptr [bp-8]
add ax,dx
mov bx,ax
mov al,byte ptr ss:[bx]
not al
mov cl,al
and byte ptr [bp-18],cl
