关于计时器

某些块需要任何一个的值absolutetime (that is, the time from the start of program execution to the present time) or过去time (for example, the time elapsed between two trigger events). Targets that support the real-time model (rtmodel) data structure provide efficient time computation services to blocks that request absolute or elapsed time. Absolute and elapsed timer features include

SeeAbsolute Time Limitationsfor more information about absolute time and the restrictions that it imposes.

定期和异步任务的计时器

Timing services provided for blocks execute withinperiodictasks (that is, tasks running at the model base rate or subrates).

The code generator also provides timer support for blocks whose execution is异步with respect to the periodic timing source of the model. See the following topics:

计时器的分配

If you create or maintain an S-Function block that requires absolute or elapsed time data, it must register the requirement (seeAccess Timers Programmatically）。在多次模型中，计时器以每速率分配。例如，考虑一个构造如下的模型：

In this case, two timers are generated, running at rates A and C respectively. The timing engine updates the timers as the tasks associated with rates A and C execute. Blocks executing at rates A and C obtain time data from the timers associated with rates A and C.

Integer Timers in Generated Code

在生成的代码中，绝对和经过的时间的计时器将作为无符号整数实现。默认大小为64位。如果指定一个值的值，这是计时器分配的内存量inf为了申请寿命（天）(Simulink) parameter. For an application with a sample rate of 1000 MHz, a 64-bit counter will not overflow for more than 500 years. SeeTimers in Asynchronous Tasks和Control Memory Allocation for Time Countersfor more information.

Elapsed Time Counters in Triggered Subsystems

Some blocks, such as the Discrete-Time Integrator block, perform computations requiring the elapsed time (delta T) since the previous block execution. Blocks requiring elapsed time data must register the requirement (seeAccess Timers Programmatically）。触发的子系统，然后根据需要分配并维护单个经过的时间计数器。该计时器在子系统级别，而不是在单个块级别上起作用。如果触发子系统（或触发子系统中的无条件执行的子系统）包含一个或多个需要经过的时间数据的块，则会生成计时器。