const EventGroupHandle_t xEventGroup,
const EventBits_t uxBitsToWaitFor,
const BaseType_t xClearOnExit,
const BaseType_t xWaitForAllBits,
TickType_t xTicksToWait );
Read bits within an RTOS event group, optionally entering the Blocked state (with a
timeout) to wait for a bit or group of bits to become set.
This function cannot be called from an interrupt.
The RTOS source file FreeRTOS/source/event_groups.c must be
included in the build for the xEventGroupWaitBits() function to be available.
The event group in which the bits are being tested. The
event group must have previously been created using a call to
A bitwise value that indicates the bit or bits to test
inside the event group. For example, to wait for bit 0 and/or bit 2 set
uxBitsToWaitFor to 0x05. To wait for bits 0 and/or bit 1 and/or bit 2 set
uxBitsToWaitFor to 0x07. Etc.
uxBitsToWaitFor must not be set to 0.
If xClearOnExit is set to pdTRUE then any bits set in the value
passed as the uxBitsToWaitFor parameter will be cleared in the
event group before xEventGroupWaitBits() returns if
xEventGroupWaitBits() returns for any reason other than a
timeout. The timeout value is set by the xTicksToWait
If xClearOnExit is set to pdFALSE then the
bits set in the event group are not altered when the call to
xWaitForAllBits is used to create either a logical AND test
(where all bits must be set) or a logical OR test (where one
or more bits must be set) as follows:
If xWaitForAllBits is set to pdTRUE then
xEventGroupWaitBits() will return when either all the bits
set in the value passed as the uxBitsToWaitFor parameter
are set in the event group or the specified block time expires.
If xWaitForAllBits is set to
pdFALSE then xEventGroupWaitBits() will return when any of the bits set
in the value passed as the uxBitsToWaitFor parameter are set
in the event group or the specified block time expires.
The maximum amount of time (specified in 'ticks') to wait
for one/all (depending on the xWaitForAllBits value) of the bits specified by
uxBitsToWaitFor to become set.
The value of the event group at the time either the event bits being waited
for became set, or the block time expired. The current value of the
event bits in an event group will be different to the returned value if
a higher priority task or interrupt changed the value of an event bit between the
calling task leaving the Blocked state and exiting the xEventGroupWaitBits()
Test the return value to know
which bits were set. If xEventGroupWaitBits() returned because its timeout
expired then not all the bits being waited for will be set. If
xEventGroupWaitBits() returned because the bits it was waiting for were set
then the returned value is the event group value before any bits were
automatically cleared because the xClearOnExit parameter was set to pdTRUE.
#define BIT_0 ( 1 << 0 )
#define BIT_4 ( 1 << 4 )
void aFunction( EventGroupHandle_t xEventGroup )
const TickType_t xTicksToWait = 100 / portTICK_PERIOD_MS;
/* Wait a maximum of 100ms for either bit 0 or bit 4 to be set within
the event group. Clear the bits before exiting. */
uxBits = xEventGroupWaitBits(
xEventGroup, /* The event group being tested. */
BIT_0 | BIT_4, /* The bits within the event group to wait for. */
pdTRUE, /* BIT_0 & BIT_4 should be cleared before returning. */
pdFALSE, /* Don't wait for both bits, either bit will do. */
xTicksToWait );/* Wait a maximum of 100ms for either bit to be set. */
if( ( uxBits & ( BIT_0 | BIT_4 ) ) == ( BIT_0 | BIT_4 ) )
/* xEventGroupWaitBits() returned because both bits were set. */
else if( ( uxBits & BIT_0 ) != 0 )
/* xEventGroupWaitBits() returned because just BIT_0 was set. */
else if( ( uxBits & BIT_4 ) != 0 )
/* xEventGroupWaitBits() returned because just BIT_4 was set. */
/* xEventGroupWaitBits() returned because xTicksToWait ticks passed
without either BIT_0 or BIT_4 becoming set. */
Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2016 Real Time Engineers Ltd.
Any and all data, files, source code, html content and documentation included in the FreeRTOSTM distribution or available on this site are the exclusive property of Real Time Engineers Ltd..
See the files license.txt (included in the distribution) and this copyright notice for more information. FreeRTOSTM and FreeRTOS.orgTM are trade marks of Real Time Engineers Ltd.