Processing system with pointer-based atm segmentation and reassembly

Abstract

Methods and apparatus for ATM segmentation and reassembly (SAR) which provide efficient transfer of ATM cell data between an ATM network and a set top box or other processing system. Reassembly operations are performed using a receive ring which stores an array of pointers. Each of the pointers specifies the address of a cell buffer suitable for storing a received ATM cell. Received ATM cells are first filtered to determine if the cells should be accepted. When a given cell is accepted, a pointer retrieved from the receive ring is used to determine the address of a cell buffer in which that cell will be stored. Host CPU software directing the operation of the SAR device periodically services the receive ring to prevent overflow. The host CPU software services the receive ring by sequentially stepping through the ring entries and linking the pointer for each stored cell into a chain of pointers maintained for the VCI on which that stored cell was received. The pointers which are linked into a chain are removed from the receive ring and replaced with pointers to empty cell buffers so that additional receive cells can be processed and stored. When an end-of-frame indicator is detected in a cell received on a given VCI, the host CPU software uses the pointers in the chain maintained for that VCI, as well as any pointers for that VCI remaining in the receive ring, to reassemble an AAL5 frame. Segmentation operations are performed using a transmit ring and similar pointer-based processing.