I. Overview
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Commercial embedded system products on the market, such as Vxwork, PSOS and Windows CE, are very mature, providing powerful development and debugging tools, but the development cost is high, and uCOS-II is a multi-tasking real-time operating system, kernel source. The code is open, short and lean, and has a strong portability, which is very suitable for some small system development. This system describes how to apply uCOS-II transplantation to the MCS51 series MCU, and discusses how to apply it to the "Embedded Device - Car GPS" system.
1. Introduction to uCOS-II
The real-time embedded operating system uCOS-II is a priority-based preemptive real-time multitasking operating system that includes real-time kernel, task management, time management, inter-task communication synchronization (semaphores, mailboxes, message queues) and memory management. . Most of the code is written in C language, the hardware-related part is written in assembly language, and its source code is publicly free.
uCOS-II is for small and medium-sized embedded systems. The kernel containing all the functional modules is about 10K. If the kernel code is only cut, it can be compressed to about 3K. The amount of RAM is related to the number of tasks in the system. The stack of tasks takes up a lot of RAM space. The size of the stack depends on the local variables of the task, the size of the buffer, and the number of possible interrupt nesting levels. The time precision of the application is determined by the system clock beat. uCOS-II requires the user to provide a periodic clock source for time delay and acknowledgment timeout. The general clock tempo should be between 10 and 100 Hz (maximum accuracy is 10 ms). Because uCOS-II checks whether there are higher priority tasks waiting for execution at every beat, if any, task switching is required, so the higher the clock tick rate, the heavier the system's extra load.
2, the system design goals
The in-vehicle mobile terminal mainly performs the following control functions:
(1) Location and related information transmission, including real-time request transmission, equal time interval transmission, and equidistant transmission. The transmission method includes GPRS mode and short message mode. Since data communication by GPRS method is charged by traffic, every 1K byte is 2- 3 cents, the cost is much lower than the SMS, so the system uses GPRS-based, SMS-assisted communication.
(2) Alarm function, divided into the following parts:
A. Specific area alarm function: After setting the alarm specific area (such as the driving task area specified by the control center), when the vehicle drives out of the set area, the monitoring center will alarm the vehicle unit and record the real-time position information of the vehicle in time.
B. Emergency alarm function: When the vehicle encounters an emergency such as robbery or traffic accident, the driver can send a distress signal to the control center through the emergency help button and upload the vehicle positioning data.
C. Anti-theft alarm function: When the vehicle is set to anti-theft status, any illegal movement of the vehicle, the vehicle-mounted unit will automatically alarm and upload the vehicle positioning data.
D. Power failure alarm function: When the main power of the vehicle unit is powered off (or manually cut off), the vehicle unit will automatically alarm and upload the vehicle positioning data.
E. It can combine automatic alarm with manual alarm: the system supports manual one-button alarm and automatic alarm function generated by intelligent device. The one-button manual alarm requires the driver to perform a quick and concealed one-button operation for quick alarm. Automatic alarms such as intelligent illegal movement alarms, the system automatically generates alarm information and sends it to the monitoring center, and saves the alarm data. The personnel of the monitoring center can take measures as needed.
(3) Power monitoring function, real-time monitoring of standby power, if it is found that the power is not enough, it will automatically switch to charging mode, and automatically cut off the charging mode after the battery is fully charged.
3, the function block of the system
The system structure diagram is shown in Figure 1. There are three layers in the outward direction: hardware circuit layer, task layer, and operating system layer.
Figure 1 system structure diagram
Second, the hardware circuit layer design
The mobile terminal of the system mainly comprises the following four parts: GPS module, GPRS module, handle, and single-chip control module, and its general functions are as follows:
(1) GPS module - used for satellite positioning data acquisition, the acquisition time interval can be set, and the minimum interval is 1 second.
(2) GPRS communication module - used to realize GPRS data transmission and reception, short message transmission and transmission and voice call function.
(3) Handle - for voice calls.
(4) Single-chip computer control module - used to control GPS, GPRS module data receiving, sending, voice call control, short message receiving and dispatching, power monitoring management and control of the car to control oil and other functions.
Third, the design of the task layer
1, system task layer composition and its priority settings
The system task layer has the following six tasks in parallel: monitoring tasks, button processing tasks, picking up tasks, GPRS tasks, short message tasks, and serial receiving tasks. Each task consists of three parts: an application, a task stack, and a task control block. Only the application is burned into ROM, and the task itself is placed in RAM, which is then set up when the system is running. The task stack is used to store the contents of the CPU registers. When a task changes from running state to other state, the contents of the CPU register are pushed into the corresponding task stack, otherwise the contents of the corresponding task stack are placed in the CPU register. As a data structure defined in the system, the contents of the task control block include the address of the task stack, the current state of the task, and the priority of the task. The operating system manages tasks by querying the contents of the task control block.
The setting of priority is determined by the execution order of each task and the size of the impact on the security of the system. The priority from high to low is: monitoring task, button processing task, pick-up task, GPRS task, short message task, serial port receiving task. This system adopts the static priority setting, that is, the task priority does not change during the running process.
2, the status of the task
There are four states in each task in this system: wait state, ready state, running state, and interrupt state. The state transition relationship is shown in Figure 2. When a task occupies the CPU, the task is in the running state, and its priority must be higher than all the ready state tasks. If the system is running and the priority of a task in the ready state is higher than the priority of the running task, the scheduling function is called, the running state task will lose the occupation right of the CPU and become ready, and the highest priority ready task is converted to Running state. Only one task can be in a running state at a time. The conversion of a task between a ready state and an operational state is called task switching. When the running task expects a certain message (that is, the data transfer between the task and the task), the task will lose the occupation right of the CPU and change to the waiting state, and the waiting time can be set by the system. If the task receives a message within the waiting time, the task will be in the ready state, otherwise it will be forced into the ready state by the time management function. The task of the running state when the interrupt occurs will be transferred to the interrupt state, and the right to occupy the CPU will be lost. Because there may be a message transmission in the interrupt, the task in the wait state is put into the ready state, so after the interrupt returns, the task scheduling function will be run first to determine the task state.
Fourth, the software layer design
This system uses μC/OS-II operating system and transplants it to MCS51 series MCU. The system uses a clock tick of Tick=50 times/second (ie 0.02 seconds/time), creating all tasks and semaphores, message tanks, message queues, etc. in main.
Void main (void)
{
OSInit();
/ / Create a semaphore, message queue;
HookSem = OSSemCreate(0); //Wake up the hook task
GprsQ = OSQCreate(&GprsMsg[0],10);
SMsgQ = OSQCreate(&SMsg[0],5);
/ / Create a memory area;
Mem20 = OSMemCreate(Part1,20,50,&err);
Mem50 = OSMemCreate(Part2,100,10,&err);
//Task creation;
OSTaskCreate(WatchDogTask,(void*)0,&WatchDogStk[0], 2); //Monitor task
OSTaskCreate((void*) KeyTask,(void*)0,&KeyTaskStk[0],3); //Key processing task
OSTaskCreate((void*)WriteTask,(void*)0,&WriteStk[0],4); //Hook up the task
OSTaskCreate((void*)GPRSTask,(void*)0,&GPRSStk[0],5); //GPRS task
OSTaskCreate((void*)SMsgTask,(void*)0,&SMsgStk[0],6); //Short message task
OSTaskCreate(ReadTask, (void *)0, &ReadStk[0],7); //Read serial port task
OSStart();
}
1, monitoring tasks
Because the system works in a highly disturbed automotive environment, although a variety of hardware anti-jamming measures such as adding a shield, reliable grounding, setting software traps, etc., may still cause the system to become chaotic due to transient disturbances, causing the system to run away. It can only be re-run by relying on the watchdog reset, so that the design goal cannot be achieved. To this end, the system uses monitoring tasks to supervise the normal operation of other tasks. If a task fails to operate normally, take corresponding measures to minimize the number of watchdog resets.
The design idea of ​​the monitoring task is: the execution time of the monitored task is predictable when it is running normally, and the monitored task sends a message to the monitoring task when it is about to run, indicating that it is running normally. When the monitored task is running, the monitoring task is in a waiting state, waiting for the monitored task to send a message to it, and the waiting time is set to the maximum time required for the expected task to operate normally. If the monitoring task receives the message within the waiting time, the task that sends the message is considered to be running normally, and the next task starts running according to the sequence of execution of each task, and the monitoring task waits for the message sent by the next task. If the waiting time has elapsed and the monitoring task has not received the message, the system's time management function will force the monitoring task to be ready. Since the priority of the monitoring task is the highest, it will seize control of the CPU and take appropriate error correction scheme.
2, button processing tasks
The button processing task mainly processes the burglar alarm, the robbing alarm, and the call button. When the task loop detects that the button is pressed, the button processing task sends a corresponding semaphore to the program for processing the corresponding button.
3, pick up the task
When the handset is picked up or the handset is lowered, an interruption occurs. In the interrupt, OSSemPost (HookSem) is called to wake up the on/off task and clear the interrupt flag. The pick-up task calls OSSemPend (HookSem, 0, & err) to get the semaphore. After obtaining the semaphore, the root pick-up status indicator determines whether it is off-hook or on-hook. When hanging up, if it was off-hook when it was ringing, then the hook-up task will treat it as a received call; if it is not off-hook when ringing, then the hook-on task will be taken when hanging up. It is treated as a dialed call.
4, GPRS task
When the serial port task receives the GPRS data, the OSQPost (GprsQ, (void *) & Gprs_Buf[0]) function is called to wake up the GPRS task. The GPRS task continuously calls gprs_msg = OSQPend (GprsQ, 50, & err) to obtain the slave serial port task. The GPRS data sent from the middle determines whether to send positioning data and related information to the control center according to the current state.
5, short message processing tasks
In the case that the GPRS network is unavailable, the system initiates a short message task for data communication. When the serial port task receives the short message, it calls OSQPost (SMsgQ, (void *) & SMsg_Buf[0]) to send a message to the short message task. The short message task continuously calls sm_msg = OSQPend (SMsgQ, 100, & err) to get the short message, and then the corresponding short message receiving and processing.
6, read the serial port task
In the read serial port task, the character string sent from the GPRS communication module and the GPS module is read from the receiving buffer, and the received string is analyzed and the corresponding processing is performed and the message is sent to the GPRS task and the short message task.
Conclusion
This paper describes the implementation of uC/OS-II on the hardware platform of MCS51, and proposes the scheme of embedded system design based on uC/OS-II for the problem of poor stability of traditional microcontroller programming method design. However, using the real-time kernel to manage these tasks increases the system's memory capacity and CPU time consumption, and the advantages of task scheduling are not well displayed. Therefore, the design has certain limitations. However, when the system's memory is large enough and the CPU runs fast enough, using the real-time kernel uC/OS-II design can improve the reliability and stability of the system, which is beneficial to the subsequent development of the system. For the W78E516, the external expansion of 32K RAM, the crystal frequency is 22.1184M, which can well meet the requirements of the system.
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