Generic Wait Functions

Wait for a certain period of time. More...

Functions
osStatus_t	osDelay (uint32_t ticks)
	Wait for Timeout (Time Delay).
osStatus_t	osDelayUntil (uint32_t ticks)
	Wait until specified time.

Description

Wait for a certain period of time.

The generic wait functions provide means for a time delay.

Note

Generic wait functions cannot be called from Interrupt Service Routines.

Function Documentation

osDelay()

osStatus_t osDelay

(

uint32_t

ticks

)

Wait for Timeout (Time Delay).

Parameters

[in]

ticks

time ticks value

Returns

status code that indicates the execution status of the function.

The function osDelay waits for a time period specified in kernel ticks. For a value of 1 the system waits until the next timer tick occurs. The actual time delay may be up to one timer tick less than specified, i.e. calling osDelay(1) right before the next system tick occurs the thread is rescheduled immediately.

The delayed thread is put into the BLOCKED state and a context switch occurs immediately. The thread is automatically put back to the READY state after the given amount of ticks has elapsed. If the thread will have the highest priority in READY state it will be scheduled immediately.

Possible osStatus_t return values:

• osOK: the time delay is executed.
• osErrorParameter: the time cannot be handled (zero value).
• osErrorISR: osDelay cannot be called from Interrupt Service Routines.
• osError: osDelay cannot be executed (kernel not running or no READY thread exists).

Note

This function cannot be called from Interrupt Service Routines.

Code Example

#include "cmsis_os2.h"
 
void Thread_1 (void *arg) {             // Thread function
  osStatus_t status;                    // capture the return status
  uint32_t   delayTime;                 // delay time in milliseconds
 
  delayTime = 1000U;                    // delay 1 second
  status = osDelay(delayTime);          // suspend thread execution
}

osDelayUntil()

osStatus_t osDelayUntil

(

uint32_t

ticks

)

Wait until specified time.

Parameters

[in]

ticks

absolute time in ticks

Returns

status code that indicates the execution status of the function.

The function osDelayUntil waits until an absolute time (specified in kernel ticks) is reached.

The corner case when the kernel tick counter overflows is handled by osDelayUntil. Thus it is absolutely legal to provide a value which is lower than the current tick value, i.e. returned by osKernelGetTickCount. Typically as a user you do not have to take care about the overflow. The only limitation you have to have in mind is that the maximum delay is limited to (2³¹)-1 ticks.

The delayed thread is put into the BLOCKED state and a context switch occurs immediately. The thread is automatically put back to the READY state when the given time is reached. If the thread will have the highest priority in READY state it will be scheduled immediately.

Possible osStatus_t return values:

• osOK: the time delay is executed.
• osErrorParameter: the time cannot be handled (out of bounds).
• osErrorISR: osDelayUntil cannot be called from Interrupt Service Routines.
• osError: osDelayUntil cannot be executed (kernel not running or no READY thread exists).

Note

This function cannot be called from Interrupt Service Routines.

Code Example

#include "cmsis_os2.h"
 
void Thread_1 (void *arg) {             // Thread function
  uint32_t tick;
 
  tick = osKernelGetTickCount();        // retrieve the number of system ticks
  for (;;) {
    tick += 1000U;                      // delay 1000 ticks periodically
    osDelayUntil(tick);
    // ...
  }
}