Received Message Descriptor in the LRM

ASIM team
LIP6 Laboratory
Paris, France

Next: PCI transactions Up: Structures in main memory Previous: Message Descriptor in the

Received Message Descriptor in the LRM

For a standard messages, the LRM is a private data structure in main memory for PCI-DDC. This structure should not be read or written by software but for composed message).

The total number of packets for a given message is computed by PCI-DDC and transmitted with the last packet of the message. The Received Packet Number is incremented by PCI-DDC at each packet received. A message is completed when the Received Packet Number matches the Expected Packet Number. There is one word dedicated for each MI allowing PCI-DDC to remember received and transmitted paquets after each packet received. All words are the LRM. In case of a Composed Message, the Expected Packet Number must be written by the software since he knows exactly the number of expected packets.

PCI-DDC suposes that structure empty (fill with 0) after reset. PCI-DDC deletes itself (written 0) word once a message is completely received.

16Expected Packet Number16Received Packet Number
&&&&&&&&&&&&&&&
§-19.5pt &&&&&&&&&&&&&&&
MI 160000h 160000h
&31&&&&&&&&&&&&&&&16& 15&&&&&&&&&&&&&&&0&
Received Message Descriptor =6pt

Each Received Message Descriptor is 4 bytes length split in 2 fields:
$\begin{mydescription} \item[Expected Packet Number] This field is written when ... ... Number] This field is incremented for each packet received.\end{mydescription}$
Both fields are reset by PCI-DDC when a received message is completed, however the software must reset the entire LRM space once at initialization.

Next: PCI transactions Up: Structures in main memory Previous: Message Descriptor in the