【正文】 eriod has beenpleted, RTX51 interrupts job0 and begins execution of job1. This functioneven reaches the timeout and the system continues with job0. The os_wait Function The os_wait function provides a more efficient way to allocate the availableprocessor time to several tasks. os_wait interrupts the execution of the currenttask and waits for the specified event. During the time in which a task waits foran event, other tasks can be executed. Wait for Timeout RTX51 uses an 8051 timer in order to generate cyclic interrupts (timer ticks).The simplest event argument for os_wait is a timeout, where the currentlyexecuting task is interrupted for the specified number of timer ticks. Thefollowing uses timeouts for the time delay. Program with os_wait Function This program is similar to the previous example with the exception that job0 isinterrupted with os_wait after counter0 has been incremented. RTX51 waitsthree timer ticks until job0 is ready for execution again. During this time, job1 isexecuted. This function also calls os_wait with a timeout of 5 ticks. The result:counter0 is incremented every three ticks and counter1 is incremented every fivetimer ticks. Wait for Signal Another event for os_wait is a signal. Signals are used for task coordination: ifa task waits with os_wait until another task issues a signal. If a signal waspreviously sent, the task is immediately continued. Program with Wait for Signal. In this example, task 1 waits for a signal from task 0 and therefore processes theoverflow from counter0. Preemptive Task Switching The full version of RTX51 provides preemptive task switching. This feature isnot included in RTX51 Tiny. It is explained here to provide a pleteoverview of multitasking concepts. In the previous example, task 1 is not immediately started after a signal hasarrived, but only after a timeout occurs for task 0. If task 1 is defined with ahigher priority than task 0, by means of preemptive task switching, task 1 isstarted immediately after the signal has arrived. The priority is specified in thetask definition (priority 0 is the default value). RTX51 Technical Data Description RTX51 Full RTX51 Tiny Number of tasks 256。 task is started when object is received. can_def_obj Define munication objects. can_get_status Get CAN controller status. can_hw_init Initialize CAN controller hardware. can_read Directly read an object’s data. can_receive Receive all unbound objects. can_request Send a remote frame for the specified object. can_send Send an object over the CAN bus can_start Start CAN munications. can_stop Stop CAN munications. can_task_create Create the CAN munication task. can_unbind_obj Disconnect the binding between a task and an object. can_wait can_write Wait for reception of a bound object. Write new data to an object without sending it. TRAFFIC: RTX51 Tiny Example Program The TRAFFIC example is a pedestrian traffic light controller that shows theusage of multitasking RTX51 Tiny Realtime operating system. During a userdefinedtime interval, the traffic light is operating. Outside this time interval, theyellow light flashes. If a pedestrian pushes the request button, the traffic lightgoes immediately into walk state. Otherwise, the traffic light workscontinuously. Traffic Light Controller Commands The serial mands that TRAFFIC supports are listed in the following mands are posed of ASCII text characters. All mands mustbe terminated with a carriage return. Command Sertal Text Description Display D Display clock, start, and ending times. Time T hh:mm:ss Set the current time in 24hour format. Start S hh:mm:ss Set the starting time in 24hour format. The traffic light controller operates normally between the start and end times. Outside these times, the yellow light flashes. End E hh:mm:ss Set the ending time in 24hour format. Software The TRAFFIC application is posed of three files that can be found in the \KEIL\C51\EXAMPLES\TRAFFIC folder. contains the traffic light controller program that is divided into the following tasks: Task 0 init: initializes the serial interface and starts all other tasks. Task 0deletes itself since initialization is needed only once. Task 1 mand: is the mand processor for the traffic light task controls and processes serial mands received. Task 2 clock: controls the time clock. Task 3 blinking: flashes the yellow light when the clock time is outside theactive time range. Task 4 lights: controls the traffic light phases while the clock time is in theactive time range (between the start and end times). Task 5 keyread