RTEMS Ada User's Guide
The GET_PACKET component of the user-provided MPCI layer is called when RTEMS must obtain a packet buffer to send or broadcast a message. This component should be adhere to the following prototype:
rtems_mpci_entry user_mpci_get_packet( rtems_packet_prefix **packet );
where packet is the address of a pointer to a packet. This routine always succeeds and, upon return, packet will contain the address of a packet. If for any reason, a packet cannot be successfully obtained, then the fatal error manager should be invoked.
RTEMS has been optimized to avoid the need for obtaining a packet each time a message is sent or broadcast. For example, RTEMS sends response messages (RR) back to the originator in the same packet in which the request message (RQ) arrived.
RTEMS Ada User's Guide
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