Computer System Having Reversible Bus Connectors

The invention relates to the field of connectors, and notably to the field of connectors for computers. It notably applies to multiprocessor environments.

The number of different types of printed circuits boards used for manufacturing a computer is increasing together with the requirement for advanced performance. The number of boards attached to a computer motherboard is thus increasing. This creates several types of problems. First, the physical size of computers increases, due to the number and volume of the different boards. Second, the number and length of signal lines on the motherboard increase; this creates routing problems and crosstalk. Third, the efficient cooling of the different boards is becoming increasingly complex and difficult to carry out.

These problems are notably encountered in multiprocessor environments. Computer performance is improving by using more and more sophisticated processors at high prices and/or by using complex implementations to gain a few percentage increase of bandwidth on DRAM or communication busses. It was therefore suggested to increase the number of processors running rather than increasing processor computation speed in order to greatly improve computer performance. Such a conventional multiprocessing system requires a large package and long signal lines. Further, since the multiprocessing system comprises a plurality of CPUs, it generates a large amount of heat compared to a single processing system.

FIG. 1 is a schematic view of such a multiprocessor system, exemplified with three different processors. The multiprocessor system of FIG. 1, comprises three processor printed circuit boards or cards 1, 2, 3, each of which includes a CPU 4, 5, 6 and a cache memory 7, 8 or 9. Each processor circuit board is connected to a common processor bus 10. The common processor bus is also connected to a memory controller 12; this controller is connected to a memory 14, e.g. a DRAM (Dynamic Random Access Memory). Each processor accesses memory 14 through the common processor bus 10 and the memory controller 12.

Accordingly, the purpose of the invention is to provide a solution to the problems discussed above, without further complicating the structure of the different boards.

According to the invention, there is provided a bus, having:

at least two parallel bus lines,

at least two connectors, each connector comprising at least two bus-terminals each connected to one bus line, and at least one terminal not connected to a bus line,

wherein:

one connector having a given pinout is the image of another connector having the same pinout in a rotation of 180 degrees,

an image in the rotation of a bus-terminal of said one connector is a bus-terminal of said another connector, and

a terminal of said one connector not connected to a bus line is electrically connected to the terminal of said another connector that is its image in the rotation.

Preferably, the image in the rotation of one given terminal having a given logic level is a terminal having an opposite logic level.

According to an embodiment of the invention, all terminals of a connector are on one side of the bus lines. The terminals may comprise power and ground terminals.

The invention also provides a circuit board, comprising:

a connector with at least two connector terminals;

switching means having connector-side terminals connected to said connector terminals, chip-side terminals, and a control input;

said switching means mapping the chip-side terminals to the connector-side terminals under control of said control input.

The control input is preferably connected to a connector terminal. The switching means may comprise two buffers, the terminals of each buffer being connected to the connector-side terminals and to the chip-side terminals, a signal received on said control input enabling either one of said two buffers.

The invention also covers a combination of a such computer board with a such circuit board.

It also provides a computer board with a bus having parallel bus lines and a least two identical connectors, and at least two identical circuit boards, each connected to one of said connectors, wherein one connector is the image of another connector in a rotation of 180 degrees, and wherein the circuit boards connected to said one connector and said another connector are relatively shifted or staggered.

Finally, the invention provides a process for routing signals on a motherboard to at least one circuit board connected in one connector of a series of identical connectors in alternate directions, comprising the steps of:

routing the signals along parallel bus lines to the connectors, thus changing the mapping of the terminals of the connectors to the bus lines between connectors in alternate directions;

switching the signals received on each circuit board according to the direction of the connector, so as to have an identical mapping of the switched signals to the bus lines, whatever the direction of the connector.

The direction of a connector may be determined in a circuit board according to the polarity of a given terminal of the circuit board connector; the step of switching preferably comprises:

storing the signals in a first buffer, in a given order;

storing the signals in a second buffer, in a different order; and

reading the signals from one of said first and second buffers.

A multiprocessor system embodying the invention will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which

FIG. 1 is a schematic view of a multiprocessor system;

FIG. 2 is a front view of the multiprocessor system according to the invention;

FIG. 3 is a view of a bus according to the invention;

FIG. 4 is a view of a card according to the invention, in a first position;

FIG. 5 is a view of the switching means of the card of FIG. 4;

FIG. 6 is a view of a possible connector pinout.

FIG. 2 is a front view of the multiprocessor system according to the invention; the multiprocessor system of FIG. 2 comprises elements similar to those of FIG. 1 and bearing the same reference numbers. The memory controller 12 is connected to the processor bus 10. Each processor circuit board 1, 2 and 3 is connected to the processor bus 10, and is arranged to be perpendicular to the processor bus.

According to the invention, and as explained below in reference to FIGS. 3 to 6, the circuit boards may be arranged on one side or the other of the bus; it is therefore possible, as depicted in FIG. 1, to limit the space used by the different circuit boards, by arranging the boards alternately on each side of the bus. In the configuration exemplified on FIG. 2, the first circuit board 1 is arranged on the right side of the processor bus, with the processor 7 facing the memory controller. FIG. 2 also shows the cooling unit 21 of the processor. The second circuit board 2 is arranged on the left side of the processor bus, with the processor 8 and the cooling unit 22 facing away from the memory controller. The third circuit board 3 is arranged like the first one. Reference numeral 23 identifies the cooling unit of the processor 9 of the third circuit board. Thus, the overall space used by the processor circuit boards is limited, even though the same boards may be used. In other words, in the structure of FIG. 2, the computer board comprises a bus having parallel bus lines and three identical connectors, and three identical circuit boards, each connected to one of said connectors; each connector is the image of the adjacent connector in a rotation of 180 degrees, and the circuit boards connected to the adjacent connectors are relatively shifted.

In the configuration of FIG. 2, voltage regulator sockets 24, 26 and 28 for the different processor boards are arranged on alternate sides of the processor bus, on the same side as the corresponding processor circuit boards. The structure of FIG. 2 has the following advantages. The distance between the successive socket assemblies on the processor bus can be reduced, the length of the bus can be shortened, and, finally, a package size of the multiprocessing system can be minimised. Furthermore, bus lines routing is straightforward, and the lines can have large line insulation, which reduces crosstalk. The CPU dedicated voltage regulators can be provided very close to each CPU, and consequently, signal line length between each CPU and each CPU dedicated voltage regulator can be reduced. Therefore, the voltage drop between the two can be reduced. Furthermore, the successive circuit boards constitute channels for airflow, so that the cooling of the different processors and voltage regulators is more efficient.

The staggered structure described in reference to FIG. 2 may be used not only for processor boards, but for any type of boards. It is particularly useful for boards that have significant thickness on part of their surface--such as processor boards, which have a cooling unit installed on the processor.

FIG. 3 is a view of a bus assembly according to the invention. The bus of FIG. 3 comprise a series of bus lines 30.sub.1 to 30.sub.n, where n is the number of bus lines, e.g. n=64 in a usual computer configuration. These lines are parallel and are connected to a controller 32. The bus also comprises a series of connectors 34.sub.1 to 34.sub.m, where m is the number of connectors, e.g. m=4 for a multiprocessor configuration. The different connectors have the same pinout; however, a given connector 34.sub.i is rotated through 180 degrees with respect to an adjacent connector 34.sub.i+1. FIG. 3 shows the centre of rotation A of the rotation that transforms connector 34.sub.2 into connector 34.sub.3 (and vice-versa). All connectors have the same pinout, and comprise a polarising key 35.sub.i that mechanically distinguishes the direction of a connector.

Each connector comprises a series of bus-sockets 36.sub.i,j, where 1.ltoreq.i.ltoreq.m and 1.ltoreq.j.ltoreq.n, each of which is connected to a different bus line. Each connector also comprises a series of sockets 38.sub.i,k, where 1.ltoreq.i.ltoreq.m and 1.ltoreq.j.ltoreq.p, that are not connected to a bus line. These sockets may for instance comprise power supply sockets, ground sockets, identifying sockets for identifying each connector, a reset socket for separately resetting a card connected to a given connector, etc. These sockets may be arranged as shown in FIG. 3 on one side of the bus lines; they may also be arranged on both sides of the bus lines, according to the needs.

According to the invention, an image in the rotation of a bus-socket of one connector is a bus-socket of the adjacent connector. In other words, the image in the rotation of the assembly {36.sub.i,j, 1.ltoreq.j.ltoreq.n} of all bus-sockets of connector i is the assembly {36.sub.i+1,k, 1.ltoreq.k.ltoreq.n} of all bus-sockets of connector i+1. Since there is only one invariant point in a rotation, this means that there exists at least one bus-socket connected to a given bus line, the image of which is not connected to the same bus line. In the case depicted in FIG. 3, the image in the rotation of bus-socket 36.sub.i,j is bus socket 36.sub.i+1,n+1-j : the image of a bus socket connected to a given bus line is therefore a bus-socket connected to a different bus-line.

On the other hand, a socket 38.sub.i,k that is not connected to a bus line, and its image the image 38.sub.i+1,k may very well be electrically connected, that is may have the same function, or be connected to the same line or plane of the board. This is indeed possible, since there is no constraint that the lines between all sockets not connected to the bus lines and their respective images be parallel.

In other words, according to the invention, in the rotation that transforms connector i into connector i+1:

each bus-socket is transformed into a bus socket connected to a different bus line;

each socket not connected to a bus line is transformed into a socket, to which it is electrically connected.

This means that the bus lines are parallel, and that the lines connecting the other sockets to their respective images are not parallel.

The bus described in reference to FIG. 3 is adapted to provide the structure described in reference to FIG. 2, with the cards or circuit boards described below. FIG. 4 is a view of a card according to the invention; such a card comprises a connector adapted to be connected to a bus connector; in the exemplified embodiment, the connector 40 is a pin connector adapted to be connected to the socket connector of FIG. 3. Connector 40 thus comprises n+p pins, and a recess 42 corresponding to the polarising key 35 of the socket connector. Out of the n+p pins, n bus pins, say bus pins 44.sub.h, 1.ltoreq.h.ltoreq.n are connected to the bus sockets 36 when the connector 40 is connected to the socket connector. The p other pins, say pins 46.sub.h, 1.ltoreq.h.ltoreq.p are connected to the sockets 38 when the connector 40 is connected to the socket connector.

The card of FIG. 4 may be connected to any one of the socket connectors of FIG. 3, and thus, one given bus pin 44.sub.h, 1.ltoreq.i.ltoreq.n may be connected to different bus lines, according to the socket connector in which the card is inserted. In the example of FIG. 3, bus pin 44.sub.h would be connected to bus socket 36.sub.h, and thus to bus line 30.sub.h or 30.sub.n+1-h, according to the socket connector. On the other hand, the pins 46.sub.h, 1.ltoreq.i.ltoreq.p of the card are connected to the same logical or electrical signal, whatever the connector into which the card is plugged.

In order to ensure proper operation of the card, whatever the socket connector into which it is plugged, the card comprises also switching means 48. The connector-side terminals 50h of the switching means are connected to the 44.sub.h of the connector, and the chip-side terminals 52.sub.h of the switching means 48 provide signals that may be used in the card, e.g. in a microprocessor chip. The switching means ensure that whatever the connector into which the card is plugged, the chip-side terminals of the switching means are correctly mapped to the bus lines. In other words, the switching means ensure that for any value h, 1.ltoreq.h.ltoreq.n, the chip-side terminal 52.sub.h of the switching means 48 are connected or mapped on the bus line 30.sub.h.

Thus, the card according to the invention may be plugged in any connector of the bus described in reference to FIG. 3: the switching means will in any case ensure a correct mapping of the chip terminals to the bus lines.

In the example given above, in a first connector 34.sub.i, socket 36.sub.j is connected to bus line 30.sub.j ; socket 36.sub.j is connected to bus pin 44.sub.j, that is connected to connector-side terminal 50.sub.j ; the switching means ensure that chip-side terminal 52.sub.j is directly connected to connector-side terminal 50.sub.j. On the other hand, in a connector 34.sub.i+1 arranged in the opposite direction, 36.sub.j is connected to bus line 30.sub.n+1-j ; socket 36.sub.j is connected to bus pin 44.sub.j, that is connected to connector-side terminal 50.sub.j ; the switching means ensure that chip-side terminal 52.sub.n+1-j is connected to connector-side terminal 50.sub.j. Thus, chip-side terminal 52.sub.n+1-j is correctly mapped to bus line 30.sub.n+1-j.

Switching means may be embodied and controlled in a plurality of ways. FIG. 5 is a view of a possible embodiment of the switching means. The switching means are controlled by the signal received on a given pin of the connector 40, say pin 46.sub.q, Sockets 38.sub.q and 38.sub.n+1-q are respectively connected to opposite logical levels, say level "0" for socket 38.sub.q, and level "1" for socket 38.sub.n+-q, In the case of a connector in a first direction, say connector 34.sub.1 in the example of FIG. 3, pin 46.sub.q is connected to socket 38.sub.q, that is to "0"; thus, the switching means 48 receive a control signal that is a logical "0". In the case of a connector in the opposite direction, say connector 34.sub.2 in the example of FIG. 3, pin 46.sub.q is connected to socket 38.sub.n+1+q ; thus, the switching means 48 receive a control signal that is a logical "1". This clearly makes it possible to command the switching means, according to the direction of the connector into which the card is plugged. Obviously, the switching means may be integrated in a chip, if necessary.

FIG. 5 simply shows how the switching means may, under control of the signal received on pin 46.sub.q, switch the connector-side terminal 50.sub.h either to chip-side terminal 52.sub.h or to chip-side terminal 52.sub.n+1-h, and respectively, terminal 50.sub.n+1-h either to chip-side terminal 52.sub.n+1-h or to chip-side terminal 52.sub.h As depicted on FIG. 5, pin connector 44.sub.h is connected to connector-side terminal 50.sub.h, and pin connector 44.sub.n+1-h is connected to connector-side terminal 50.sub.n+1-h. The control signal received on pin 46.sub.q is transmitted to a control input terminal 54. The signal received on control input terminal 54 is provided to an inverter 56.

The signal received on connector-side terminal 50.sub.h (respectively 50.sub.n+1-h) is provided to two buffers 58.sub.h and 60.sub.h (respectively 58.sub.n+1-h and 60.sub.n+1-h). The outputs of buffers 58.sub.h and 60.sub.n+1-h are connected to chip-side terminal 52.sub.h ; the outputs of buffers 58.sub.n+1-h and 60.sub.h are connected to chip-side terminal 52.sub.n+1-h. Buffers 58.sub.h and 58.sub.n+1-h are enabled by the signal provided on control input terminal 54, whereas buffers 60.sub.h and 60.sub.n+1-h are enabled by the signal output by inverter 56. The operation of the switching means of FIG. 5 is clear.

In the embodiment of FIG. 5, the switching means are operating in one direction only. They may be duplicated in order to ensure routing of the signals to and from the card; one may also provide other embodiments, e.g. a bidirectional buffer, or a switch. In the embodiment of FIG. 5, the signals of two sockets are used in order to control the switching means; there are other ways to control the switching means, e.g. two different pins of the connector 40 may be used, one pin only being connected to a given logical level, according to the direction of the connector.

FIG. 6 is a view of a possible connector pinout, according to the invention. FIG. 6 shows the bus lines 30.sub.1 to 30.sub.16, a first card connector 62, with a control pin 64, corresponding to pinout 46.sub.1, and a second connector 66, with a control pin 68, corresponding to pinout 46.sub.1. As shown on FIG. 6, control pin 64 is connected to VCC, whereas control pin 68 is connected to ground, so as to ensure a correct mapping of the chip-side terminal of the switching means to the bus lines.

It is clear that the scope of invention not only covers the example described in reference to FIG. 3, where each connector is the image of an adjacent connector after a rotation through 180 degrees, but also other configurations, where some of the connectors are arranged in the same direction as the adjacent connectors: it is sufficient that at least one connector is the image of an adjacent connector in a rotation of 180 degrees. For instance, the scope of the invention covers the configuration where two connectors are arranged on one side of the bus lines, and where the two next connectors are arranged on the other side of the bus lines. It is also not necessary that all connectors have exactly the same pinout. One could imagine that two different types of connectors are provided on a given bus. The invention is also not limited to the exemplified pinout of the preferred embodiments described above.

Also, the invention was described above in the usual configuration where the bus connectors are socket connectors, and the circuit boards connectors are pin connector. It should be understood that the invention is not limited to this configuration, and that the usual types of edge connectors provided in the computer industry may also be used. The words "connector terminal" thus notably cover pins, sockets, edge lands and spring terminals adapted to mate with such lands.

Furthermore, it is clear for the person skilled in the art that the bus lines of the invention are parallel in that they do not intersect. This is the proper meaning in the invention of the word parallel; it is not necessary that the bus lines are "parallel" in the mathematical meaning of this word to ensure the advantages of the invention.