ASIM team LIP6 Laboratory Paris, France

Packet

Pages are the smallest entities from the software point of view but not from the hardware point of view. Pages are broken into packets by PCI-DDC. The packet is the physical exchange unit. The packet length is variable, and is dynamically adapted to the PCI burst length and the HSL-network. PCI-DDC does not guarantee that a page will be transferred as one packet if page length is more than one aligned word. Each packet contains all the informations necessary to reconstruct the message in the remote memory (including the physical remote address and the message identifier).

Basically, PCI-DDC try to send a page in only one packet, but a page will be split in the following cases:

• There is contention on the HSL-network. It is no worth locking the PCI-bus and PCI-DDC closes the packet.
• PCI-bus is preempted (due to latency timer mechanism for example). It is no worth locking HSL-network and PCI-DDC closes the packet.
• The Maximum Packet Length (MPL) has been reached, and PCI-DDC closes the packet. This maximum length is software defined by a configuration register (see chapter ).

Server design A. Fenyö mpc@mpc.lip6.fr - contact people About this Web Site $Date: 1998/02/14 17:06:25 $

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