US 6,289,386 B1 · 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.

Claims14

Dependent claims

A serial communication adapter which comprises:

a receive buffer for storing received data frames having a maximum frame size, wherein the receive buffer has a predetermined storage capacity;
a receive controller coupled to the receive buffer, wherein the receive controller is configured to track the amount of available buffer space in the receive buffer by maintaining an available buffer space value, wherein the available buffer space value is increased by an amount corresponding to less than the maximum frame size in response to receiving frames having a size less than the maximum frame size;
a transmit controller configured to send a buffer credit in response to a credit signal, wherein the buffer credit is indicative of available space for a data frame in the receive buffer;
a buffer credit manager coupled to the receive controller to receive a receive flag for each received complete data frame and coupled to the transmit controller to receive a transmit flag for each buffer credit sent, wherein the buffer credit manager maintains a committed space value corresponding to additional committed buffer space, wherein the committed space value is incremented by an amount corresponding to the maximum frame size in response to the transmit controller sending a buffer credit and is decremented by the amount corresponding to the maximum frame size in response to the receiver buffer receiving a data frame, wherein the buffer credit manager includes a comparator configured to compare the committed space value to the available buffer space value and is configured to assert the credit signal in response to determining that the available buffer space is greater than the additional committed buffer space by at least the maximum frame size.

1 more element

A system network comprising a remote node and a local node coupled by a serial communications link, wherein the remote node is configured to transmit a data frame having a maximum frame size to the local node only if the remote node receives a buffer credit from the local node indicative of available receive buffer space for a data frame, wherein the local node includes a network interface unit for coupling to the serial communications link, and wherein the network interface unit includes:

a receive buffer for storing received data frames having a maximum frame size, wherein the receive buffer has a predetermined storage capacity;
a receive controller coupled to the receive buffer, wherein the receive controller is configured to track available buffer space in the receive buffer by maintaining an available buffer space value, wherein the available buffer space value is increased by an amount corresponding to less than the maximum frame size in response to receiving frames having a size less than the maximum frame size;
a transmit controller configured to send a buffer credit in response to a credit signal, wherein the buffer credit is indicative of available space for a data frame in the receive buffer;
a buffer credit manager coupled to the receive controller to receive a receive flag for each received data frame and coupled to the transmit controller to receive a transmit flag for each buffer credit sent, wherein the buffer credit manager maintains a committed space value corresponding to additional committed buffer space, wherein the committed space value is incremented by an amount corresponding to the maximum frame size in response to the transmit controller sending a buffer credit and is decremented by the amount corresponding to the maximum frame size in response to the receiver buffer receiving a data frame, wherein the buffer credit manager includes a comparator configured to compare the committed space value to the available buffer space value and is configured to assert the credit signal in response to determining that the available buffer space is greater than the additional committed buffer space by at least the maximum frame size.

1 more element

Dependencies are inferred from the claim text.

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

Life of this patent

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

Life of this patent

Abstract

Claims14