Description
Creates a message queue. A message queue allows tasks or ISRs to send pointer-sized variables (messages) to one or more tasks. The meaning of the messages sent are application specific.
Files
os.h/os_q.c
Prototype
Arguments
p_q
is a pointer to the message queue control block. It is assumed that storage for the message queue will be allocated in the application. The user will need to declare a “global” variable as follows, and pass a pointer to this variable to OSQCreate():
OS_Q MyMsgQ;
p_name
is a pointer to an ASCII string used to name the message queue. The name can be displayed by debuggers or µC/Probe.
msg_qty
indicates the maximum size of the message queue (must be non-zero). If the user intends to not limit the size of the queue, simply pass a very large number. Of course, if there are not enough OS_MSGs in the pool of OS_MSGs, the post call (i.e., OSQPost()) will simply fail and an error code will indicate that there are no more OS_MSGs to use.
p_err
is a pointer to a variable that is used to hold an error code:
OS_ERR_NONE
If the call is successful and the mutex has been created.
OS_ERR_CREATE_ISR
If OS_CFG_CALLED_FROM_ISR_CHK_EN set to 1 in os_cfg.h: if attempting to create the message queue from an ISR.
OS_ERR_OBJ_PTR_NULL
If OS_CFG_ARG_CHK_EN is set to 1 in os_cfg.h: if p_q is a NULL pointer.
OS_ERR_Q_SIZE
If OS_CFG_ARG_CHK_EN is set to 1 in os_cfg.h: if the size specified is 0.
OS_ERR_ILLEGAL_CREATE_RUN_TIME
If OS_SAFETY_CRITICAL_IEC61508 is defined: you called this after calling OSSafetyCriticalStart() and thus you are no longer allowed to create additional kernel objects.
Returned Value
None
Required Configuration
OS_CFG_Q_EN must be enabled in os_cfg.h. Refer to uC-OS-III Configuration Manual
Callers
Application.
Notes/Warnings
- Queues must be created before they are used.