Sun Microsystems, Inc.

Tom Lyon

Rasoul Mirzazadeh Oskouy

Terrence C Miller

Evan W Adams

Prakash Kashyap

David Hendricks

A control memory is provided for storing the control and state information of a number of virtual direct memory access (DMA) channels. A control memory arbiter and a control memory data bus are also provided to arbitrate accesses to the control memory to facilitate asynchronous transmit and receive. Separate areas in the control memory are provided for storing the control and state information of the transmit DMAs, and the receive DMAs. Additionally, descriptive information about the transmit/receive data ring and its descriptor, the data packet being transferred and its cells are also stored for the transmit and receive DMAs. The control memory is also used to stored a programmable bandwidth group (BWG) table comprising a plurality of BWG index entries for bandwidth selection. A Segmentation And Reassembly (SAR) module which cellifies transmit packets and reassembly receive packets on the host computer is also provided for segmenting transmit packets into transmit cells for transmission, and reassembling receive cells into receive packets. Two series of FIFOs are provided for staging the transmit and receive cell payloads. Lastly, complement to the SAR module, a media cell manager (MCM) module is provided for packing the transmit cell payloads before their transmission, and unpacking the receive cell payloads upon their receipt. The cyclic redundancy check (CRC) value for each transmit packet is calculated incrementally. Transmit tags are used to differentiate the transmit cell payloads from the packet header and packing instructions; and receive tags are used to differentiate the receive cell payloads from the packet header and the end of packet marker.

Multi-virtual DMA channels, multi-bandwidth groups, host based

In a computer system having a hierarchical file structure, a file system is provided which permits users of the system to share a file hierarchy and also have a private hierarchy in which files are automatically copied to as they are modified. Through the system of the present invention, a directory appears to the user as a single directory but may actually comprise files originating from a number of directories which are connected to one another through search links. Each directory has a search link associated with it which contains the path name of the back layer or directory behind it. The first layer seen through the system of the present invention is the front layer, private to the user. The back layers behind the front layer and connected to the front layer through the search links are shared layers accessible to multiple users. Thus transparent to the user of the directory accessible comprises multiple layers comprising shared and private files. The system further provides a copy-on-write feature which protects the integrity of the shared files by automatically copying a shared file into the users private layer when the user attempts to modify a shared file in a back layer.

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Palo Alto, CA, United States of America

Tom Lyon