Idle and R_RDY Primitive Signals

Idle and R_RDY are Primitive Signals that are used between Frames to maintain bit, byte, and word synchronization, to keep links active between Frames, and to do link level flow control. They are also used to allow the receiving circuitry time to finish processing of a Frame before the next Frame arrives. The R_RDY signal is sent from a receiver to a transmitter to notify of the availability of a Frame buffer and any other required resources for buffer-to-buffer Credit for receiving a Frame, as described in the R_RDY section, on page 95. The Idle is a true idle, which is transmitted to maintain activity on the link while data or control information isn t being sent, and to provide processing time between Frames. Idles are discarded at the receiver as soon as they are recognized.

To ensure that the receiver has sufficient processing time between Frames, each transmitter must transmit a minimum of six Primitive Signals between each Frame, of which the first two and last two must be Idles (allowing processing of any R_RDY signals). The Fabric may insert or remove Idles between Frames as long as the destination receives at least two Idles preceding each Frame. This is done for speed-matching Ports with different clock frequencies, and for Intermix, when Frames are inserted or removed by the Fabric.

Start of Frame Delimiter

The Start of Frame (SOF) delimiter is an Ordered Set,...