The present invention relates to an asynchronous communication system, and more particularly relates to full duplex communications using single-phase two-line coding.
As a result of the rapid increase in the scale of semiconductor chips, factors that determine circuit operations have shifted almost entirely from devices to interconnections. The delay in global interconnections has hindered the progress of clock frequencies. Accordingly, there is a demand for an approach in a different direction from current approaches. Clocks based on asynchronism, in which overall management is accomplished by connecting modules that act locally in local clocks or the like to each other using asynchronous communications, are one approach that can solve the abovementioned problem of deep-core intercommunications. In particular, asynchronous point-to-point communications make it possible to establish flexible physical structures in the near-future large-scaled systems-on-a-chip.
There are various types of data encoding that allow asynchronous data transfer, including 4-phase 2-line encoding and 2-phase 2-line encoding. In both cases, timing information must be included in latent form in the data; accordingly, the length of code words is increased. Such an encoding style requires a large number of lines; consequently, as communication channels increase, the complexity of interconnections becomes increasingly deeper. Furthermore, the large number of steps required for asynchronous handshake operations result in a long cycle time. Corresponding to this, it may be concluded that reducing the complexity of communication steps used for asynchronous operation, which does not require extra line resources, is the most important subject in asynchronous communication systems having a high bandwidth.
[A method in which] communications are performed in one direction in an asynchronous manner using a 2-color 1-phase 2-line encoding has been published by the inventors of the present invention (see Non-Patent Document 1). However, full duplex asynchronous 2-color 1-phase 2-line encoding has not yet been realized.
Non-Patent Document 1: Tomohiro Takahashi et al. “Asynchronous Data Transfer Scheme Based on Simultaneous Control in a Bidirectional Way and Its VLSI Design”, IEICE Trans. on Electronics, Vol. J87-C, No. 5, pp. 459-468 (May 2004) (Japanese).
[Problems to Be Solved by the Invention]
An object of the present invention is to provide a full duplex asynchronous data transfer system based on 1-phase 2-line encoding.
In order to achieve the abovementioned object, the present invention is a full duplex asynchronous communication system for performing full duplex asynchronous communications between two modules, characterized in comprising transmission means provided to each of the abovementioned modules, for superimposing and transmitting parity signals and data signals used for requests; signal generating means located between the abovementioned two modules, for generating signals C from signals A and B in which parity signals and data signals used for requests from the abovementioned two modules are superimposed; “acknowledge” detection means provided to each of the abovementioned two modules, for receiving the abovementioned signals C and detecting from the received signals C whether or not the parity signals from the two modules match each other; and decoding means provided to each of the abovementioned modules, for decoding the transmitted data signals from the received signals C in cases in which the parity signals match each other in the abovementioned “acknowledge” detection means.
The present invention is also a module of a full duplex asynchronous communication system for performing full duplex asynchronous communications between two modules, comprising a transmission means for superimposing and transmitting parity signals and data signals used for requests; “acknowledge” detection means for receiving signals C from signal generating means located between the abovementioned two modules and used to generate signals C from signals A and B in which the parity signals and data signals used for requests from the abovementioned two modules are superimposed, and detecting from the received signals C whether or not the parity signals from the two modules match each other; and decoding means for decoding the transmitted data signals from the received signals C in cases in which the parity signals match each other in the abovementioned “acknowledge” detection means.
“Acknowledge” detection and decoding can be performed in a simple manner when the abovementioned signal generating means generates signals C by determining the sum of the signals A and B in which the parity signals A and B used for requests from the abovementioned two modules are superimposed, and when the “acknowledge” detection means performs “acknowledge” detection by using the received signals C to detect whether to threshold values are exceeded or not exceeded, and the abovementioned decoding means performs decoding by subtracting the data transmitted by the decoding means themselves from the received signals C.
A full duplex asynchronous communication system and modules can be realized using a simple circuit structure when the abovementioned transmission means, the abovementioned “acknowledge” detection means, and the abovementioned decoding means are constructed from multiple-valued current-mode logic circuits, and the abovementioned signal generating means is formed with wiring that connects the abovementioned modules.
[Effect of the Invention]
In the abovementioned structure of the full duplex asynchronous communication system of the present invention, both modules can operate as though the modules were independent, and data transfer from both modules can be performed in a single step. Furthermore, “acknowledge” detection and decoding can be performed in a simple manner, and can be realized by means of a simple circuit structure if multiple-valued current-mode logic circuits are used.
In the 1-phase 2-line encoding used for the full duplex asynchronous data transfer system of the present invention, “ODD” and “EVEN” parity information (colors) is multiplexed on the same two lines along with data from a primary module (PM) and a secondary module (SM). When parity information is transmitted as request signals from both the primary module and the secondary module, asynchronous communications are performed by detecting whether or not the parity information is the same. This protocol allows mutual overlapping of the control signals. This control signal overlapping system reduces the communication steps for the cycle; as a result, low-power-consumption asynchronous data transfer can be realized at a high speed. It is important to detect an applicable state on the basis of the mixed 2-line encoding. The corresponding parity information is detected by calculating the sum of the 2-line code words, and the data is decoded by subtracting the source data from the 2-line code words. This combination of decoding allows full duplex asynchronous data transfer using only two lines; as a result, a great reduction in communication lines can be realized.
Multiple-valued current-mode logic (MVCML) circuits were used for circuit packaging. The reason for this is that the linear sum of current modes can be realized on wires without using active elements; the proposed asynchronous circuit is therefore simplified. Furthermore, as a result of the use of multiple-valued current signals, control signals and data can be superimposed on the same wiring, making full duplex communications possible. Test chips were provided, and it was found that the proposed full duplex asynchronous communication system could be realized. Using the test chips, the proposed system and a conventional system were compared in terms of communications steps, number of lines, cycle time, power consumption, chip area, and throughput.
Embodiments of the present invention will be described in detail with reference to the attached drawings.
In order to achieve asynchronous point-to-point communications that are not dependent on any variation in the delay, a model is discussed which has a wiring delay between modules having a limited wiring delay (the data is always delivered at some point in time); however, the upper limit is unknown (an accurate value of when the data is delivered is not known). As is shown in
Subsequently, code words C that include “acknowledge” of the mutual requests are sent in the “acknowledge” mode to the primary module PM and secondary module SM. The system is devised so that in the “acknowledge” mode, code words C are created from the code words A and B, and so that it can be detected from these code words C that the request signals (i.e., colors) were the same as “acknowledge” signals. This protocol allows both modules to operate independently of each other.
As a result of such simultaneous operation, 1-step communications are possible; as is shown in
In 1-phase 2-line encoding for duplex communications, “data” which stipulates 2-line logical values and “color” which stipulates parity values are separately defined. The data (xD, x′D) code words and color code words (xC, x′C) on two lines are defined as shown in
(xP,x′P)=(xD,x′D)+(xC,x′C)=(xD+xC,x′D+x′C)
(xS,x′S)=(xD,x′D)+(xC,x′C)=(xD+xC,x′D+x′C) [Equation 1]
The code words C(x, x′) are expressed on the respective lines as the sum of the respective components of the code words A and B.
(x,x′)=(xP,x′P)+(xS,x′S)=(xP+xS,x′P+x′S) [Equation 2]
b) shows the code words (x, x′) corresponding to mutual combinations of data and color as eight effective states. The term “effective state” refers to the attempted transfer of logical values (respective data: “0” or “1”) in the same color (ODD or EVEN) by the primary module and secondary module; in this state, the two requests match each other and can be transferred. In cases in which the colors match each other as shown in
a) shows the assignment of the code words (x, x′) in the coordinate plane. Here, the horizontal axis of the coordinate plane expresses x, and the vertical axis expresses x′. The mutual correspondence between colors (meaning the mutual arbitration between requests for asynchronous data transfer) can be detected by calculating the sum of x+x′ and using two types of threshold values (2.5 and 5.5), as shown in
In cases in which the logical values of one pair within the primary module PM and secondary module SM are (“0”, “1”) or (“1”, “0”), the code words (x, x′) have the same values of (1, 1) for ODD, and (3, 3) for EVEN, respectively. However, in the PM, data from the SM can be specified by subtracting the source data (xP, x′P) from the code words (x, x′). A similar operation can be performed in the SM as well. These operations are shown in the table shown in
<Circuit Packaging>
A packaging method that can be used to mount the asynchronous communication system of the present invention is multiple-valued current-mode logic (MVCML). The reason for this is that packaging in an MVCML circuit can be accomplished by connecting lines by linear addition, and an arbitration function can be realized by wiring between the modules.
a) shows a circuit diagram of the interface for full duplex communications in the present invention. This is a symmetrical structure; the primary module PM and secondary module SM have the same constituent elements. The constituent elements are an encoding circuit EC, a color detection circuit CD, a decoding circuit DC, and several control circuits.
In the encoding circuit EC shown in
In the primary module PM and secondary module SM, current signals (x/2, x′/2), which are divided in ½ increments by the color detector CD (see
In the decoders DC (see
Furthermore, in all of the control signals, a low level is assigned to ODD, and a high level is assigned to EVEN.
<Evaluation>
Thus, it was confirmed that the full duplex asynchronous data transfer of the present invention can be mounted.
The table shown in
The channels of the full duplex asynchronous communication system of the present invention are realized using only two lines, and the throughput reaches 2 Gbps. This system is suitable for intra-chip communications in SoC applications in which the modules are positioned at intermediate or long distances. The reason for this is that the propagation time between modules is greatly reduced.
Furthermore, in the model and the like described above, a description was given using the terms primary module and secondary module; however, these terms “primary” and “secondary” are merely used in order to distinguish between the two modules; between the two communicating modules, both modules perform a communication function in the same manner without distinction as to “primary” or “secondary.” Furthermore, the term “module” means “constituent unit”, and in the case of this invention, means “unit performing communications.”
Number | Date | Country | Kind |
---|---|---|---|
2005-062910 | Mar 2005 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2006/302699 | 2/16/2006 | WO | 00 | 9/5/2007 |