Renesas 70 Place a task in a finite time wait state by specifying a timeout value

Chapter 3 Introduction to MR308

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The time management function provides system time management, time reading36, time setup37, and the func-

tions of the alarm handler, which actuates at preselected times, and the cyclic handler, which actuates at prese-

lected time intervals.

The MR308 kernel requires one timer for use as the system clock. There are following time management ser-

vice calls that are provided by the MR308 kernel. Note, however, that the system clock is not an essential func-

tion of MR308. Therefore, if the service calls described below and the time management function of the MR308

are unused, a timer does not need to be occupied for use by MR308.

• Place a task in a finite time wait state by specifying a timeout value

A timeout can be specified in a service call that places the issuing task into WAITING state.38 This

service call includes tslp_tsk, twai_flg, twai_sem, tsnd_dtq, trcv_dtq, trcv_mbx, tget_mpf, vtsnd_dtq,

and vtrcv_dtq. If the wait cancel condition is not met before the specified timeout time elapses, the er-

ror code E_TMOUT is returned, and the task is freed from the wait state. If the wait cancel condition is

met, the error code E_OK is returned.

The timeout time should be specified in ms units.

tslp_tsk(50)

READY state

tslp_tsk(50)

iwup_tsk

E_OK

E_TMOUT

WAITING state

RUN state

Timeout value

Figure 3.38 Timeout Processing

MR308 guarantees that as stipulated in µITRON specification, timeout processing is not performed

until a time equal to or greater than the specified timeout value elapses. More specifically, timeout

processing is performed with the following timing.

1. If the timeout value is 0 (for only dly_tsk)

The task times out at the first time tick after the service call is issued.

2. If the timeout value is a multiple of time tick interval

The timer times out at the (timeout value / time tick interval) + first time tick. For example, if the

time tick interval is 10 ms and the specified timeout value is 40 ms, then the timer times out at

the fifth occurrence of the time tick. Similarly, if the time tick interval is 5 ms and the specified

timeout value is 15 ms, then the timer times out at the fourth occurrence of the time tick.

3. If the timeout value is not a multiple of time tick interval

The timer times out at the (timeout value / time tick interval) + second time tick. For example, if

the time tick interval is 10 ms and the specified timeout value is 35 ms, then the timer times out

36 get_tim service call

37 set_tim service call

38 SUSPENDED state is not included.