OCEOS/oceos inter-task communication/dataq
Data Queue
Data Queue Introduction
These are FIFO queues of non-null void pointers ordered by arrival time. Each queue has an associated pending jobs queue, and two associated atomic operations, read and write. A size operation gives the number of pointers on the queue, and the data queue create operation sets the maximum size of the queue.
The read operation returns the first pointer on the queue unless the queue is empty. Unlike many other OS, the job that performs the read operation does not block if the queue is empty. Instead OCEOS provides three options for the read operation to determine what should happen in that case:
- In the oceos_dataq_read_continue() option if the queue is empty a null pointer is returned and the job proceeds taking this into account.
- In the oceos_dataq_read_restart() or oceos_dataq_read_restart_timeout() options if the queue is empty the job terminates and will restart from its beginning when the queue is written or the timeout occurs.
- A job that was started as a result of a timeout does not terminate if it comes to oceos_dataq_read_restart_timeout() and the data queue is still empty, a null pointer is returned to show there was a timeout and the job continues.
A pointer is added to the queue by write. All jobs on the pending list are moved to the ready queue and also removed from the timed actions queue if present.
The pending queue order of jobs with the same priority is preserved in the transfer. The scheduler is then activated and may pre-empt the current executing job.
In case the queue is full, the new entry can be dropped or the oldest entry overwritten, depending on an option chosen when the data queue is created. An appropriate status is returned and a log entry is made if the new entry is dropped.
Note
If timeouts are used with data queues the hardware specific timer initialization and handling must be set up by the developer please see here.
Data Queue Configuration
User must define NUMBER_OF_DATAQS. If NUMBER_OF_DATAQS is zero, data queues are not used. The example can be found in OCEOS demo projects.
User must create defined number of data queues before calling oceos_init_finish()#define NUMBER_OF_DATAQS 2 /* * Create the application configuration structure */ struct application_configuration app_config = {0}; app_config.number_of_data_queues = NUMBER_OF_DATAQS;
API Functions
| Directive | Description | main | task | IRQ handler |
|---|---|---|---|---|
| oceos_dataq_create() | Create data queue | * | ||
| oceos_dataq_write() | Puts pointer to the data on data queue. | * | * | |
| oceos_dataq_read_continue() | Read data queue next item. | * | ||
| oceos_dataq_read_restart() | Read data queue next item. | * | ||
| oceos_dataq_read_restart_timeout() | Read data queue next item. | * | ||
| oceos_dataq_get_size() | Returns number of items on the data queue | * | * | |
| oceos_dataq_penq_get_size() | Returns number of jobs on the dataq pending job's queue | * | * | |
| oceos_dataq_clear() | Clears data queue and frees tasks on pending queue | * | * |
oceos_dataq_create()
Header File
dataq.h
Description
Create data queue.
This directive creates the specified data queue with specified queue size and pending jobs queue size. Roll-over on the queue can also be enabled/disabled. Roll-over means that if the queue is full new entries will overwrite the oldest ones on the queue. If use_timeout = TRUE, timed actions must be initialized, please see herePrototype
enum DIRECTIVE_STATUS oceos_dataq_create( dataq_t dataq_id, // data queue ID U16_t dataq_size, // data queue size U16_t pen_q_size, // pending jobs queue size BOOLE_t roll_over, // whether to roll over when full BOOLE_t use_timeout // whether timeout is used oceos_dataq_read_restart_timeout );Parameters
Parameter Description dataq_id Data queue ID dataq_size Data queue size pen_q_size Pending jobs queue size roll_over Whether to roll over when full use_timeout Whether timeout is used in oceos_dataq_read_restart_timeout() Returns
This function returns enum DIRECTIVE_STATUS.
enum DIRECTIVE_STATUS Description NOT_CONFIGURED System meta pointer is NULL INCORRECT_STATE Init meta pointer is NULL INVALID_ID Dataq ID is out of range TOO_MANY Dataq ID exceeds dataq number in configuration file INVALID_NAME Dataq ID is not available (already in use) INVALID_NUMBER Dataq_size or pen_q_size is out of range INVALID_SIZE Dataq pen_q_size <= 0 SUCCESSFUL All is OK Example Usage
enum DATAQ_NAME{ d_apple, d_orange, }; enum DIRECTIVE_STATUS status; status = oceos_dataq_create(d_apple, 13, 4, 0, TRUE); if(SUCCESSFUL != status){ // Handle ERROR } // if
oceos_dataq_write()
Header File
dataq.h
Description
Puts pointer to the data on data queue. Pointer to the data must not be NULL.Prototype
enum DIRECTIVE_STATUS oceos_dataq_write( dataq_t dataq_id, // data queue ID void* data // non-null pointer to data );Parameters
Parameter Description dataq_id Data queue ID data Non-null pointer to data Returns
This function returns enum DIRECTIVE_STATUS.
enum DIRECTIVE_STATUS Description NOT_CONFIGURED System meta pointer is NULL INCORRECT_STATE Init meta pointer is NULL INVALID_ID Dataq ID is out of range INVALID_ADDRESS Data pointer is NULL TOO_MANY Dataq is full or Ready Q is full (check system log)
INTERNAL_ERROR Wrong task index on pending Q or Failed to remove task from timed action Q if timeout is used
SUCCESSFUL All is OK Example Usage
enum DATAQ_NAME{ d_apple, d_orange, }; char *mes = "OCEOS"; enum DIRECTIVE_STATUS status; status = oceos_dataq_write(d_apple, mes); if(SUCCESSFUL != status){ // Handle ERROR }
oceos_dataq_read_continue()
Header File
dataq.h
Description
Read data queue, if empty it returns NULL.Prototype
void* oceos_dataq_read_continue( dataq_t dataq_id // data queue ID );Parameters
Parameter Description dataq_id Data queue ID Returns
This function returns void*.
void* Description NULL System check ERROR (check system log) data Pointer to the data Example Usage
enum DATAQ_NAME{ d_apple, d_orange, }; void* data; data = oceos_dataq_read_continue(d_apple); if(NULL == data){ // Handle ERROR }
oceos_dataq_read_restart()
Header File
dataq.h
Description
Read data queue next item. If data queue is empty, task is put on pending queue for this data queue and restarted by oceos_dataq_write(). Restarted task will lose any data stored in variables on the stack so it may be necessary for the application to store such data elsewhere so that it is available when the task restarts.Prototype
void* oceos_dataq_read_restart( dataq_t dataq_id // data queue ID );Parameters
Parameter Description dataq_id Data queue ID Returns
This function returns void*.
void* Description NULL System check ERROR or Task was originally started from data queue pending queue or data queue pending queue is full (check system log)
data Pointer to the data Example Usage
enum DATAQ_NAME{ d_apple, d_orange, }; void* data; data = oceos_dataq_read_restart(d_apple); if(NULL == data){ // Handle ERROR }
oceos_dataq_read_restart_timeout()
Header File
dataq.h
Description
Read data queue next item. This directive returns the oldest pointer from the data queue. If the queue is empty the task is put on the pending queue to be restarted when new data is available on the queue by oceos_dataq_write() or by timeout if timeout parameter is != 0. A 64-bit timeout in microseconds can be set, after which the task will be removed from the pending queue and NULL will be returned. If a timeout value of zero is passed then the job will remain on the pending queue until a data queue pointer is available.Note
In order to use timeouts, timed actions must be configured, please see here and data queue is created with timeout parameter set to TRUE.
Restarted task will lose any data stored in variables on the stack so it may be necessary for the application to store such data elsewhere so that it is available when the task restarts.
Prototype
void* oceos_dataq_read_restart_timeout( dataq_t dataq_id, // data queue ID U64_t timeout // timeout, restart time if no entry, 0 => ignore );Parameters
Parameter Description dataq_id Data queue ID timeout Timeout, restart time if no entry, 0 => ignore Returns
This function returns void*.
void* Description NULL System check ERROR or Task was originally started from data queue pending queue or timeout data queue pending queue is full (check system log)
Data Pointer to the data Example Usage
enum DATAQ_NAME{ d_apple, d_orange, }; void* data; data = oceos_dataq_read_restart_timeout(d_apple, 10000); if(NULL == data){ // Handle ERROR }
oceos_dataq_get_size()
Header File
dataq.h
Description
Returns number of items on the data queue with ID.Prototype
int oceos_dataq_get_size( dataq_t dataq_id // data queue ID );Parameters
Parameter Description dataq_id data queue ID Returns
This function returns int.
int Description -1 ERROR >= 0 Number of Items on data queue with ID Example Usage
enum DATAQ_NAME{ d_apple, d_orange, }; int count; count = oceos_dataq_get_size(d_apple); if(-1 == count){ // Handle ERROR }
oceos_dataq_penq_get_size()
Header File
dataq.h
Description
Returns number of jobs on the data queue pending job's queue.Prototype
int oceos_dataq_penq_get_size( dataq_t dataq_id // data queue ID );Parameters
Parameter Description dataq_id Data queue ID Returns
This function returns int.
int Description -1 ERROR >= 0 Number of Items on data queue with ID Example Usage
enum DATAQ_NAME{ d_apple, d_orange, }; int count; count = oceos_dataq_penq_get_size(d_apple); if(-1 == count){ // Handle ERROR }
oceos_dataq_clear()
Header File
dataq.h
Description
Clears data queue and frees tasks on pending queue.Prototype
enum DIRECTIVE_STATUS oceos_dataq_clear( dataq_t dataq_id // data queue ID );Parameters
Parameter Description dataq_id Data queue ID Returns
This function returns enum DIRECTIVE_STATUS.
enum DIRECTIVE_STATUS Description NOT_CONFIGURED System meta pointer is NULL INCORRECT_STATE Init meta pointer is NULL INVALID_ID Data queue ID is out of range INTERNAL_ERROR Wrong task index on pending queue or Failed to remove task from timed action queue if timeout is used
SUCCESSFUL All is OK Example Usage
enum DATAQ_NAME{ d_apple, d_orange, }; enum DIRECTIVE_STATUS status; status = oceos_dataq_clear(d_apple); if(SUCCESSFUL != status ){ // Handle ERROR }