“7.33 MAILBOX FUNCTIONS ‏ل سح‎ ಶಜಧ

+ message-mailbox is for an IPC message that can be used onl
sage 8 message-pointer or can be

the mailbox for an error- i j i
ण ‏مہ‎ ಗಡ த tror-handling task, which handles the different
Figure 7.9(a) shows three mailbox-types at the different RTOSes. Figure 7.9(b) shows the initialization
and other functions for a mailbox at an OS. The following may be the provisions at an OS for IPC functions
when using the mailbox.
1. A task may put into the mailbox only a pointer to the message-block or number of message bytes as per
the OS provisioning.
2. There are three types of the mailbox provisions.

A queue (Section 7.12) may be assumed a special case of a mailbox with provision for multiple messages
or message pointers. An OS can provide for queue from which a read (deletion) can be on a FIFO basis or
alternatively an OS can provide for the multiple mailbox messages with each message having a priority
parameter. The read (deletion) can then only be on priority basis in case mailbox message has multiple messages
with priority assigned to high priority ones. Even if the messages are inserted in a different priority, the
deletion is as per the assigned priority parameter.

An OS may provision for mailbox and queue separately. A mailbox will permit one message pointer per box
and the queue will permit multiple messages or message pointers. ൮005-11 RTOS is an example of such an OS

The RTOS functions for mailbox for the use by the tasks can be the following:

1. OSMBoxCreate creates a box and initializes the mailbox contents with a NULL pointer.
2. OSMBoxPost sends (writes) a message to the box.