Efficient communication between components of an integrated circuit is always challenging, especially within integrated circuits that include a large number of communicating elements. A rich communication fabric is essential for modern data-centric digital circuits, but each physical wire that carries data consumes valuable area and power resources in the circuit. A communication fabric that is too rich for the activities that its attached components are performing is wasted by the communication fabric sitting idle for long periods of time, while a communication fabric that is too lean creates idle components waiting for data bottlenecks to clear in the communication fabric. Serializing data to reduce the number of transmission wires is one alternative to minimize power and area of a communication network, but that comes at an increased transmission latency. Further, such serial communication, to be most effective, should operate at a higher frequency than the elements that create the parallel data, otherwise the operation of the entire system slows. Integrated circuits that operate at frequency sufficiently high enough that serial communication can occur without performance penalty, i.e., integrated circuits that include communication portions that operate many multiples faster than data generation portions, can be difficult to provide. Not many modern integrated circuits have such high-frequency resources available to them.
FIG. 1 illustrates example communication systems within an integrated circuit 15 in the prior art. Of course, typical integrated circuits may contain thousands or hundreds of thousands of communication channels, and those illustrated in FIG. 1 are simple instructional examples.
Communication paths can be uni-directional or bi-directional. Bi-directional communication sends data either way between two communication nodes. Uni-directional communication paths send data from a sender to a receiver. An example of uni-directional communications is described in U.S. Pat. No. 6,816,562. Even in “uni-directional” paths, some data, such as protocol data or information may travel backwards from the receiver to the sender—such as sending an “acknowledge” signal after the receiver has received the data. As used in this disclosure, the term “unidirectional” communication is generally used when desired data is sent only from a sender to a receiver, without regard to protocol information, which may travel in any direction. Variants of the invention are equally applicable to both uni-directional and bi-directional communication.
Referring back to FIG. 1, in the most simple case, a data sending node, sending node, or sender 20 sends data to a data receiving node, receiving node, or receiver 22 over a communication channel 24. In most instances within an integrated circuit the communication channel 24 is a metal trace that carries electrical signals, but other communication methods are known in the art. After the data is received, the receiver 22 may acknowledge that it has received the data. In a bi-directional scheme, data could be sent in either direction over the data channel 24.
In the next example, a sender 30 sends data to a receiver 32. In this example, there are four data channels 34 that operate in parallel. Thus, in one data communication cycle four pieces of data can be transferred between the sender 30 and the receiver 32. Also included in the data channels 34 is a set of data storage nodes 36, one for each channel 34. The storage nodes 36 may be designed and configured to store more than one piece of data. For example, each storage node 36 may be configured to store ten pieces of data. An example of such a storage node 36 is a FIFO (First In First Out) storage, also known as a queue. FIFOs are useful in data communication because they store data in the order received until the data is ready to be used. FIFOs are especially useful in systems where the sender 30 and receiver 32 are not synchronized—i.e., in those systems where the sender 30 does not know if the receiver 32 is in a state ready to accept data. By instead loading data from the sender 30 into a FIFO, the receiver 32 can access the data whenever it is ready.
In the next example, a sender 40 sends data to a receiver 42. In this example, the sender 40 outputs eight bits of parallel data that are ‘serialized’ into, for example, one or two communication channels 46 by a serializer 44. At the destination, a de-serializer 48 converts the serialized data back into eight bits of parallel data for use by the receiver 42. By using a serializing system, fewer communication channels are used than the number of parallel bits output by the sender 40, which can be a benefit in systems that may have long or many communication channels. Routing one or two wires between the sender 40 and the receiver 42 uses less resources than routing eight parallel wires. There is an extra cost, however, in that both a serializer 44 and a de-serializer 48 are added to the system cost, for each communication path that uses such a system. Additionally, unless the serializer runs at a higher clock speed than the sender 40 and receiver 42, the overall data transmission speed of the data between the sender 40 and receiver 42 is reduced, because it takes at least four or eight times as long, depending on whether there are one or two serial communication channels 46, to send the data to the receiver 42. There is further delay with converting the parallel data to serial data at the sender 40 side, then re-converting the data back to parallel at the receiver side 42, although some of these actions may be performed in parallel. Even more delay may be caused by communication protocol overhead, such as by sending a signal informing the receiver that there is data ready to be sent, and sending an acknowledgement after the data has been received. Such serial systems are common in the prior art, even given their deficiencies, due to the space savings of not having to run parallel communication paths throughout the integrated circuit.
A difficulty lies in striking a balance between a communication system that is too richly connected and one that uses minimal resources while simultaneously being easy to integrate into the communication system.
Embodiments of the invention address these and other limitations in the prior art.