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Message Mailboxes

Table C-9 shows the API for message mailbox management. Note that µC/OS-III does not directly provide services for managing message mailboxes. Given that a message mailbox is a message queue of size one, µC/OS-III can easily emulate message mailboxes.

 

µC/OS-II (os_mbox.c)

µC/OS-III (os_q.c)

Note

void *

OSMboxAccept(

OS_EVENT *pevent);

 

(1)

OS_EVENT *

OSMboxCreate(

void *pmsg);

void

OSQCreate(

OS_Q *p_q,

CPU_CHAR *p_name,

OS_MSG_QTY max_qty,

OS_ERR *p_err);

(2)

void *

OSMboxDel(

OS_EVENT *pevent,

INT8U opt,

INT8U *perr);

OS_OBJ_QTY,

OSQDel(

OS_Q *p_q,

OS_OPT opt,

OS_ERR *p_err);

 

void *

OSMboxPend(

OS_EVENT *pevent,

INT32U timeout,

INT8U *perr);

void *

OSQPend(

OS_Q *p_q,

OS_TICK timeout,

OS_OPT opt,

OS_MSG_SIZE *p_msg_size,

CPU_TS *p_ts,

OS_ERR *p_err);

(3)

INT8U

OSMBoxPendAbort(

OS_EVENT *pevent,

INT8U opt,

INT8U *perr);

OS_OBJ_QTY

OSQPendAbort(

OS_Q *p_q,

OS_OPT opt

OS_ERR *p_err);

 

INT8U

OSMboxPost(

OS_EVENT *pevent,

void *pmsg);

void

OSQPost(

OS_Q *p_q,

Void *p_void,

OS_MSG_SIZE msg_size,

OS_OPT opt,

OS_ERR *p_err);

(4)

INT8U

OSMboxPostOpt(

OS_EVENT *pevent,

void *pmsg,

INT8U opt);

 

(4)

INT8U

OSMboxQuery(

OS_EVENT *pevent,

OS_MBOX_DATA *p_mbox_data);

 

(5)

 

    1. Message Mailbox API
      1. In µC/OS-III, there is no “accept” API since this feature is built into the OSQPend() by specifying the OS_OPT_PEND_NON_BLOCKING option.
      2. In µC/OS-II, OSMboxCreate() returns the address of an OS_EVENT, which is used as the “handle” to the message mailbox. In µC/OS-III, the application must allocate storage for an OS_Q, which serves the same purpose as the OS_EVENT. The benefit in µC/OS-III is that it is not necessary to predetermine the number of message queues at compile time. Also, to create the equivalent of a message mailbox, you would specify 1 for the max_qty argument.
      3. µC/OS-III returns additional information about the message received. Specifically, the sender specifies the size of the message as a snapshot of the current timestamp is taken and stored as part of the message. The receiver of the message therefore knows when the message was sent.
      4. In µC/OS-III, OSQPost() offers a number of options that replaces the two post functions provided in µC/OS-II.
      5. µC/OS-III does not provide query services, as they were rarely used in µC/OS-II.
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