Method and apparatus for partitioning data load and unload functions

Abstract

The asynchronous transfer mode (ATM) interface, which may be a segmentation and reassembly unit, controls segmentation of packets into cells and reassembly of cells into packets for interconnecting a computer system to an ATM system. An architecture is disclosed which partitions load and unload functions within the ATM interface. The load and unload functions are separately partitioned for segmentation and for reassembly. For segmentation, a transmit load engine controls storage of data from packets into an external buffer memory; whereas transmit unload engine handles extracting data from the memory, segmenting the data into cells, and transmitting the cells to the ATM system. For reassembly, a receive load engine handles receiving and storing the cells corresponding to the packets into a memory; whereas a receive unload engine controls extraction of the data from the memory and transmission of the packets to the computer system. Communication between the partitioned load and unload engines is achieved using a scheduler queue. For segmentation, the transmit unload engine schedules operation of the transmit load engine by specifying particular virtual or physical data connections for servicing within the scheduler. The transmit load engine services the data connections in the order appearing in the scheduler queue. A data connection is scheduled either when new packets are available on a previously idle connection or when a data queue within the memory containing data for segmentation reaches a nearly empty threshold. Similar logic is employed for facilitating communication between the receive load engine and the receive unload engine with several minor differences.