Implementation of a divide algorithm for buffer credit calculation in a high speed serial channel

Abstract

A network interface unit which implements a low latency algorithm for buffer credit calculation. In one embodiment, a system network is provided with a remote node coupled to a local node by a serial communications link. The remote node is configured to transmit a data frame to the local node only if the remote node receives a buffer credit which indicates that the local node has available receive buffer space for a data frame. The local node includes a network interface unit for coupling to the serial communications link, and the network interface unit includes a receive buffer, a receive controller, a transmit controller, and a buffer credit manager. The receive controller stores incoming data frames in the receive buffer until they can be forwarded to the i/o bus of the local node. The transmit controller is configured to send buffer credits to the remote node in response to a credit signal from the buffer credit manager. The buffer credit manager is coupled to the receive controller to receive a receive flag for each data frame which is completely received by the receive buffer, and coupled to the transmit controller to receive a transmit flag for each buffer credit sent. The buffer credit manager iteratively determines the committed buffer space from the amount of data stored in the receive buffer and the receive and transmit flags, and generates the credit signal using a comparator which compares committed-but-unoccupied buffer space to the available space in the receive buffer, and asserts the credit signal if the available buffer space is greater than the committed buffer space by at least the maximum frame size.