Patent ID: 6249756
Filing Date: 2001-06-19
Classification: G06F

Abstract:
An improved flow control system for use in a communication system having interconnected transmit and receive nodes connected by physical links, with the magnitude of internode round trip communication delays dependent on the length of the physical link between nodes and the magnitude of node logic delays, and with a receive node indicating a READY state when it is ready to receive words and indicating a BUSY state when it is unable to receive words, said system comprising:a receive FIFO having an input into which words received from the link are pushed and an output from which received words are pulled, with the receive FIFO capable of holding a first predetermined number of words and overflowing if words are pushed faster than pulled and more words accumulate than the first predetermined number, with a first number, designated a low watermark, and a second number, designated a high watermark, and with the low watermark being less than the high watermark and the high watermark being less than the first predetermined number, with said receive FIFO having capacity above said high watermark to accumulate receipt of delayed words transmitted after a BUSY state is indicated without overflowing;a flow controller, coupled to said receive FIFO for controlling said receive FIFO, said flow controller configured to:indicate a READY state if the number of words accumulated in the receive FIFO is less than the low watermark;indicate a BUSY state if the number of words accumulated in the receive FIFO is greater than the high watermark;while in the BUSY state and while the number of words accumulated in the receive FIFO is greater than the low watermark;to send an N word credit message to the sending node when a number of words pulled from said FIFO exceeds a second predetermined number (N) so that the sending node may send an additional N words while the BUSY state is indicated.