DYNAMIC WAVE-PIPELINED INTERFACE APPARATUS AND METHODS THEREFOR

Abstract: An apparatus and method for a dynamic wave-pipelined interface are implemented. Data signals received from a sending circuit delayed via a programmable delay device corresponding to each signal before being latched into the receiving device. The programmable delay in each delay device is set according to an initialisation procedure whereby each signal is deskewed to a latest arriving signal. Additionally, a phase of an input/output (I/O) clock controlling the latching of the data signals is adjusted so that a latching transition is substantially centred in a data valid window.

Description: DYNAMIC WAVE-PIPELINED INTERFACE APPARATUS AND METHODS THEREFOR TECHNICAL FIELD The present invention relates in general to data processing systems, and in particular, to bus interfaces in data processing systems. BACKGROUND INFORMATION As system clock speeds have increased in data processing systems, reflecting an increase in the speed of central processing units, the speed of transfers on buses in the system has had to increase correspondingly. The transfer of data across a bus connecting elements of the data processing system is necessarily limited by the physical separation of the elements . One method which has been developed to transfer data across a bus is wave-pipelining in which a data signal is launched on the bus before the previous data has been captured into a receiving device across the bus. In other words, data is pipelined across the bus interface between elements in a data processing system in essentially an "assembly line" fashion. Once the "pipeline" or "assembly line" is filled, data is delivered at an average rate that exceeds the latency across the interface. In a typical data processing system, data may be transferred from a source device to a plurality of receiving devices. Different receiving devices will be coupled to the source, or sending, device across bus interfaces having differing electrical lengths, and therefore differing latencies. Additionally, in a single device receiving a plurality of data signals, each signals may have a different latency. Variations may arise from manufacturing tolerances, design limitations, for example variations in line lengths, and time dependent effects, such as data dependent jitter (inter-symbol interference), clock jitter, and noise. Moreover, data is expected to be delivered synchronously. That is, data is expected to be delivered on a predetermined cycle of the system clock. If data is delivered earlier or later than expected, errors may occur. In a wave-pipelined interface, timing analysis is made more complicated because both the fast path and slow path are equally important. The data valid region, that is the time interval during which data can be reliably sampled, is reduced as the difference in time between the fast path and the slow path coupling the source, or sending, device to one or more receiving devices increases. If the difference in time between the fast path and the slow path becomes as large as the period of the bus clock, synchrony will be lost. Moreover, skew in the sampling clock may further reduce the data valid region. As bus interface speeds increase, smaller timing variations between the fast and slow paths are required, and clock skew constraints become more severe. However, the control of clock skew and timing variations may be limited by physical constraints presented by the layout of the data processing system. Therefore, there is a need in the art for methods and apparatus to deskew the data at the receiving device end of the interface, and increase the time during which data can be reliably sampled. It is an object of the present invention to provide a technique which alleviates the above drawbacks. SUMMARY OF THE INVENTION According to the present invention we provide an interface apparatus comprising: a plurality of delay devices, each device being operable for receiving a corresponding data signal, each delay device having a preselectable delay time, and outputting said data signal after said preselected delay time; and circuitry coupled to said plurality of delay devices operable for setting each preselectable delay time, each preselected delay time being set in response to an arrival time associated with each data signal. Also according to the present we provide a method of dynamic wave-pipelining in an interface comprising the step of setting an arriving edge of each data signal of a plurality of data signals to correspond to an arriving edge of a latest arriving data signal in said plurality of data signals. The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken m conjunction with the accompanying drawings, m which: FIGURE 1 illustrates, m block diagram form, a data processing system m accordance w th an embodiment of the present invention; FIGURE 2 illustrates, n block diagram form, an embodiment of a dynamic wave-pipelined interface m accordance w th the present invention; FIGURE 3 schematically illustrates an input timing diagram for the interface of FIGURE 2; FIGURE 4 illustrates, m block diagram form, a data receive unit n accordance with an embodiment of the present invention; FIGURE 5A illustrates, m flowchart form, a methodology m accordance with an embodiment of the present invention; FIGURE 5B illustrates, m flowchart form, a method of clock adjustment according to an embodiment of the present invention; FIGURE 5C schematically illustrates a timing diagram corresponding to the method of FIGURE 5B, FIGURE 5D illustrates, in flowchart form, a method of data deskewing m accordance with an embodiment of the present invention; FIGURE 5E schematically illustrates a timing diagram corresponding to the method of FIGURE 5D; FIGURE 5F illustrates, n flowchart form, a method of clock phase adjustment according to an embodiment of the present invention; and FIGURE 5G schematically illustrates a timing diagram corresponding to the method of FIGURE 5F. DETAILED DESCRIPTION The present invention provides a wave-pipelined mechanism that implements mitigation of data timing variations and clock itter. In an initialization procedure, the size of the data valid region may be increased with a corresponding reduction m the sensitivity of the interface to timing variations between chips on a bus. Timing variations among a plurality of data signals input to the receiving device are removed by determining the earliest and latest arriving data signals, and delaying the earliest arriving data signal by a preselected amount determined by the arrival time difference between the earliest and latest arriving data signals Additionally, skew m a bus clock from the sending device is removed whereby the latch clock derived therefrom is substantially centred m a data window. In the following description, numerous specific details are set forth such as bus clock frequencies, clock edges, etc. to provide a thorough understanding of the present invention However, it will be obvious to those skilled m the art that the present invention may be practised without such specific details In other instances, well-known circuits have been shown m block diagram form m order not to obscure the present invention m unnecessary detail Refer now to FIGURES 1-5G wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. A representative hardware environment for practising the present invention is depicted m FIGURE 1, which illustrates a typical hardware configuration of data processor 113 m accordance with the subject invention having central processing unit (CPU) 110, such as a conventional microprocessor, and a number of other units interconnected via system bus 112. Data processor 113 includes random access memory (RAM) 114, read only memory (ROM) 116, and input/output (I/O) adapter 118 for connecting peripheral devices such as disk units 120 and tape drives 140 to bus 112, user interface adapter 122 for connecting keyboard 124, mouse 126, and/or other user interface devices such as a touch screen device (not shown) to bus 112, communication adapter 134 for connecting workstation 113 to a data processing network, and display adapter 136 for connecting bus 112 to display device 138. CPU 110 may include other circuitry not shown herein, which will include circuitry commonly found within a microprocessor, e.g., execution unit, bus interface unit, arithmetic logic unit, etc. CPU 110 may also reside on a single integrated circuit. Referring now to FIGURE 2 illustrating a wave-pipelined interface 200 m accordance with the present invention. Interface 200 is incorporated m each of chip 202 and chip 204 which communicate data with each other via a respective interface 200. In an embodiment of the present invention, chips 202 and 204 may, for example, correspond to CPU 110 and RAM 114 m data processor 113. Data is transferred between chips 202 and 204 at a rate determined by a bus clock, such as, bus clocks 206 and 208. Bus clocks 206 and 208 are nominally the same frequency, and are derived from reference clock 210 provided to a PLL, PLL 212 m each of chips 202 and 204. In an embodiment of the present invention, reference clock 210 may be a system clock. Each of PLL 212 outputs a local clock, local clock 214 in ch p 202 and local clock 216 m chip 204 which is locked m phase to reference clock 210, and may be a preselected integer, M, multiple of the period of reference clock 210. Local clock 214 is buffered by driver 218 to provide bus clock 206 output from chip 202 Similarly, local clock 216 is buffered by driver 220 to provide bus clock 208 output from chip 204 The bus clock s provided along with the data signals communicated from the chip. Data 222 from chip 202 is latched into output latch 224 and driven and buffered by driver 226. The data s latched on a preselected edge of local clock 214. The data is received via multiplexer (MUX) 228. MUX 228 also receives a predetermined synchronisation pattern m conjunction with an initialisation alignment procedure (IAP) . These will be further described below. Data 222 is buffered by receiver (RX) 230 and provided to an data receive unit 232. Bus clock 206, sent along with data 222, s buffered by RX234, the output of which forms I/O clock 236, also provided to data receive unit 232. Data from chip 204 being sent to chip 202, along with bus clock 208, is similarly received by interface 200 m ch p 202, and it would be understood that the description of data receive unit 232 to follow applies equally well m the receipt of data by chip 202 from chip 204. Refer now to FIGURE 3 m which is schematically illustrated a timing diagram for data 222 arriving at an input to chip 204 Although the timing will be described with respect to data 222, interface 200 is bi-directional, and it would be understood that a similar diagram would equally apply for data being transmitted from chip 204 to chip 202. A first data signal, data 302 arrives after a nominal latency arising from the finite transit time on the path between chips 202 and 204. Data 302 is illustrated m FIGURE 3 arriving at a fiducial time, T 0 . A second data signal, data 304 has a latency that is longer than the latency of data signal 302, and is delayed relative to the fiducial time by an amount T s which will be taken to be a maximum delay from among a plurality of delayed data signals on data bus 222. Similarly, a third data signal, data 306, has a shorter latency than the nominal and arrives earlier than data 302. Data 306 is illustrated as having an arrival time which precedes the fiducial, T 0 by T f . For the purpose of describing the operation of data receive unit 232 below, T £ will be taken to represent the earliest arrival time from among a plurality of early data signals on data bus 222 The difference m arrival times of the data on data bus 222 will be referred to as data skew Data skew may arise from several sources, including manufacturing tolerances, design limitations, such as, variations in line lengths, and time dependent effects, for example, data dependent jitter (inter-symbol interference), clock jitter and noise. (In FIGURE 3, fiducials have been illustrated with respect to the centres of transitions, for ease of illustration m the schematic timing diagrams. It would be understood by an artisan of ordinary skill that valid transitions may be specified with other predetermined percentages of steady state values ) Data is latched into the receiving device, such as chip 204, on an edge of I/O clock 236 In the absence of data skew, data may be captured within a data valid window w th a width of the period of I/O clock 236 Data skew reduces the width of the data valid window, T w , by the sum of T £ and T s . In order to restore the width of the data valid window, interface 200 m accordance w th the present invention inputs a plurality of data signals to data receive unit 232, illustrated n FIGURE 4. Data is buffered by a receiver 230 and coupled to a programmable delay line, one of delay lines 406 through 408. Programmable delay lines 406 through 408 provide a preselected amount of delay m the corresponding data signal input to the delay line. The delay line receiving the latest arriving data signal, corresponding to data 304 m FIGURE 3, is programmed for zero delay. (It would be understood that any circuit has a minimum propagation t me. Zero delay would be further understood to be relative to any such minimum propagation time.) Thus, if for example, m FIGURE 4, data 402 corresponds to data 304 of FIGURE 3, delay line 408 is programmed for zero delay. Delay lines receiving the other data signals are programmed for increasing amounts of delay wherein the delay line receiving the data signal having the earliest arrival, corresponding to data 306 m FIGURE 3, is programmed for the longest delay. Thus, if for example, m FIGURE 4, data 404 corresponds to the earliest arriving data signal, then delay line 408 is programmed for a longest delay value. In this way, all of the data signals input to chip 204, data 402 through data 404 are deskewed to the latest arriving data signal. Although, the embodiment of the present invention illustrated in FIGURE 4 has been shown, and described, m conjunction with individual data signals, it would be understood that the principles of the present invention may be applied to groups of data signals, such as a data byte, or other such groupings of data signals Such an alternative embodiment would be within the spirit and scope of the present invention. Delay lines 406 through 408 are programmed to have their preselected delay values via an initialisation alignment procedure (IAP) The IAP may be performed on power up or reset of data processing system 100 incorporating dynamic wave pipeline interface 200. In an embodiment of the present invention, IAP may be controlled by a signal from CPU 110 m FIGURE 1 In the IAP, a predetermined synchronisation (sync) pattern s sent across data bus 222 by asserting IAP mode select 240, whereby MUX 228 outputs the predetermined sync pattern The sync pattern is sent on all data signals constituting data bus 222. The sync pattern s captured into latches 412 through 414 which receive the output of delay lines 406 through 408. Data input into latches 412 through 414 are latched on an edge of I/O clock 236 which is derived via buffer 234 from bus clock 206. I/O clock 236 is delayed m delay line 410 m data receive unit 232. The delayed I/O clock is repowered m buffer 416 and provided to latches 412 through 414. The control of delay line 410, as well as delay lines 406 through 408 is via state machine 418. During the IAP, state machine 418 adjusts the programmable delays m each of delay lines 406 through 408 and 410 m response to capture of the sync pattern m latches 412 through 414. Outputs 420-422 are coupled to corresponding inputs of data compare logic 424. A suitable sync pattern permits unambiguous resolution of synchronous data capture m the absence of any data skew. One such pattern constitutes the data value sequence "100010001000". This sequence is periodic and has a periodicity of four I/O clock periods, and is used m conjunction with an elastic interface, having an elasticity of four-clock periods. An elastic interface is the subject of the co-pending, commonly-assigned U.S. Patent Application entitled "An Elastic Interface Apparatus and Method Therefor, " which has been incorporated herein by reference. Other sync patterns may alternatively be implemented provided any such sync pattern permits unambiguous resolution of synchronous data capture. For example, a sync pattern complementary to the data value sequence above may alternatively be implemented. The selection of the delays m delay lines 406 through 408, and 410 will now be described m conjunction with the operation of state machine 418. Refer now to FIGURE 5A illustrating methodology 500 for selecting the delays via state machine 418. In step 502, the I/O clock is adjusted to the last arriving data signal by selecting a suitable delay m delay line 410. Step 502 will be further discussed m conjunction w th FIGURES 5B and 5C. The data signals are deskewed m step 504, which will be further described m conjunction with FIGURES 5D and 5E . In step 508, the I/O clock sample point is adjusted. Step 508 will be further described m conjunction with FIGURES 5F and 5G below. Refer now to FIGURE 5B illustrating a flow diagram of I/O clock delay step 502. In step 512, the IAP s initiated with a launch of the sync pattern as previously described. In step 514, state machine 418, in FIGURE 4, determines the sync pattern latched into latches 412 through 414 correspond to the same data signal, which for the exemplary sync pattern described above is the value "1". State machine 418 determines if the same data signal has been latched by determining if output 426 of set-reset (S-R) flip-flop 428 has been reset. Output 426 of S-R flip-flop 428 is controlled by data compare logic 424, which detects miscompares and asserts its output 430 m response thereto. In response to the same data signal appearing at each of inputs 421 through 423 of data compare logic 424, output 430 is negated, whereby S-R flip-flop is reset Data compare logic 424 is gated by delayed I/O clock 411, whereby an output signal is established on output 430 of data compare logic 424 n response to the latching of data into latches 412 through 414 An exemplary embodiment of data compare logic 424, corresponding to a positive logic implementation, may form the logical NAND of the signals on inputs 421 through 423 and the gate derived from delayed clock 411. Alternatively, an exemplary embodiment, corresponding to a negative logic implementation, may form the logical OR of inputs 421 through 423 and a gate derived from the complement of delayed clock 411. Such an embodiment would correspond to the complementary sync pattern discussed above. Statistical fluctuations m setting the delays m delay lines 406 through 408 and 410 may be reduced by sampling the sync pattern over multiple cycles of delayed I/O clock 411 Delayed I/O clock 411 increments counter 432. Counter 432 asserts output 434 after a predetermined number, K, of delayed I/O clock 411 cycles, and then counter 432 rolls over Output 434 of counter 432 is coupled to reset input 436 of S-R flip-flop 428, thereby resetting output 426 A next sync pattern/m scompare detect sequence can then be performed. If m any sample a m scompare is detected, S-R flip-flop 428 is set Returning to FIGURE 5B, if during the sample period, determined by the value of the integer K, all inputs 421 through 423 of data compare logic 424 have the same data signal, step 514 follows the "Yes" path, and method 500 proceeds to step 504. In this case, with delays not yet having been set m delay lines 406 through 408, timing schematically illustrated m FIGURE 5C is representative. I/O clock 236 has been delayed through delay line 410 by an amount, T d , wherein edge t λ is within the data valid window represented by time interval, T„ Initially, the delay time, T d , may bezero, wherein edge T 0 lies outside the data valid window and edge T 0 latches the value "1" into one of latches 412 through 414 receiving data 306 and the value'O" into latches receiving data 302 and 304 A miscompare results Then, output 430 of data compare logic 424 is asserted and the output 426 of S-R flip-flop 428 is set. As a consequence, in step 514 m FIGURE 5B, the "No" branch is followed. In step 516, state machine 418 increases the delay through delay line 410. The delay is increased by state machine 418 sending an "Up" signal on count direction 438 to bi-directional counter 440. Counter 440 increments its count m response to counter 432 asserting output 434 when counter 432 reaches the end of the count determined by the value of the integer, K. The count contained m bi-directional counter 440 is supplied to delay control 442. Delay control 442 decodes the count and supplies a corresponding control signal 444 to delay line 410, whereby delay line 410 increases the delay time, T d by a predetermined time increment. (A programmable delay line 410 which may be used m the present invention is the subject of the co-pending, commonly-owned U.S. Patent Application entitled "Programmable Delay Locked Loop" incorporated herein by reference.) I/O clock delay step 502 then returns to step 514. If, m step 514, the incremented value of T d is sufficient to place edge t x into the data valid window then, step 514 follows the "Yes" branch as described above. Otherwise, the delay through delay line 410 is incremented again in step 516 and I/O clock delay step 502 loops through steps 514 and 516 until edge t x falls within the data valid window. State machine 418 then, proceeds to step 504, in which the data s deskewed. Data deskew step 504 is described m detail m FIGURE 5D. In step 504, the plurality of delay lines 406 through 408 are programmed. In step 518, a first delay line, corresponding to a first data signal, is selected for programming (This may correspond to an index, j , being initialised to a first value, which may be zero.) In step 520, a data compare is made. The data compare in step 520 is performed m exactly the same fashion as the data compare, step 514, m FIGURE 5B and therefore, will not be described again n detail here If all of the data signals are m synchronisation, then, m step 522, an increment of delay is set m the jth delay line, corresponding to the jth data signal Note that initially, because of I/O clock adjust step 502, m step 520, the "Yes" branch will be followed. After incrementing the delay, in step 522, a data compare, step 520, is again performed. Data deskew step 504 then loops between steps 520 and 522 until data synchrony is lost, and step 520 takes the "No" branch where, m step 524, the delay m the jth data signal is decremented by one delay increment. In this way, the jth data signal may be phase aligned to the I/O clock. This may be further understood by referring again to FIGURE 5C. Suppose first, by way of example, that m steps 520 and 522 the jth data signal is the latest arriving data signal, data 304. Then, adding the first increment of delay to the corresponding delay line will shift data 304 so that its edge t 2 occurs after the edge t of delayed I/O clock 411. Then, m step 520, the data compare follows the "No" branch to step 524 where the one delay increment added in step 522 is removed. Thus, for the last arriving data signal, no additional delay is added. This is the desired operation of data deskew step 504 because the last arriving data signal may be the reference for the deskewing of all other data signals. Similarly, consider now, again by way of example, the operation of steps 520 and 522 for a data signal that is the earliest arriving data signal, data 306 m FIGURE 5C. For the earliest arriving data signal, multiple increments of delay are added m its corresponding programmable delay line by repeated iterations through steps 520 and 522, until its edge t 3 is shifted in time past edge ti of delayed I/O clock 411. Then, just as previously described with respect to data 304, data compare step 520 follows the "No" branch to step 524 where the programmable delay is decremented by one delay increment and edge t 3 is aligned to edge t x of delayed I/O clock 411 After deskewing the jth data signal, m step 526 data deskew step 504 determines if all data signal delays have been programmed If not, deskew step 504 advances to the next delay line, m step 527 and returns to step 520 After all delay lines have been adjusted, all data signals are aligned with edge t of delayed I/O clock 411, as schematically illustrated in the timing diagram of FIGURE 5E, and deskew step 504 proceeds to step 506 of method 500 In clock sample point adjust step 506, delayed I/O clock 411 edge t x may be adjusted to a centre of the data valid window. Although a clock edge may be centred at launch, it may be skewed at the receiver due to path latency differences, noise, etc Sample point adjust step 506 deskews the clock signal Referring to FIGURE 5F, m step 528 a data compare is made Initially, because of data deskewing step 506, data compare step 526 follows its "Yes" branch to step 540 and the time delay programmed m delay line 410 is incremented by one time delay increment, in step 530. Clock sampling point adjust step 506 then returns to step 528 where the data compare is made again. I/O clock adjust step 506 then loops through steps 528 and 530 until a data miscompare, m data compare step 528 results, indicating that delayed clock edge t λ of delayed I/O clock 411, denoted t/ has crossed a late side, ti of the data valid window, FIGURE 5G. Then, data compare step 528 follows the "No" branch, and, m step 532, the count m counter 440 is stored. I/O clock sample adjust step 506 then determines the early side of the data valid window The delay m delay line 410 is decremented by one time delay increment, m step 534. And, n step 536, a data compare is made Because, m step 534 edge ti been shifted back into the data valid window, data compare 536 follows its "Yes" branch, and the delay programmed m delay line 410 is further decremented by a time delay increment. Clock sample adjust step 506 then loops through steps 536 and 538, until the data compare m data compare step 536 signals a miscompare This indicates that edge t l of delayed I/O clock 411, m FIGURE 5G, has arrived earlier than an early side, t e of the data valid window. This transition of delayed I/O clock 411 is denoted by tJ . Data compare step 536 then follows the "No" branch and, in step 540 the early s de count m counter 440 is stored In step 542, the phase of delayed I/O clock 411 is set to the average of the early side and late side edges of the data valid window This corresponds, m FIGURE 5G, to the solid portion of delayed I/O clock 411 curve, and edge t Delayed I/O clock sample adjust step 506 then proceeds to step 508, and method 500 exits the IAP mode. The apparatus and methods represented m the embodiments described herein provide a dynamic wave-pipelined interface The plurality of data signals arriving at the interface are deskewed relative to each other, compensating for tracking differences between the data signals, differences m the paths between the I/O clock and the data signals, and design tolerances between the data signals, for example, chip wiring, module wiring, and card wiring Consequently, the data signal region is increased m width The interface further adjusts the sampling clock to substantially centre the sampling point in the centre of the data valid window, whereby differences in the paths between the I/O clock and data, module wiring and card wiring may be compensated.

Claims: CLAIMS 1 An interface apparatus comprising a plurality of delay devices, each device being operable for receiving a corresponding data signal, each delay device having a preselectable delay time, and outputtmg said data signal after said preselected delay time, and circuitry coupled to said plurality of delay devices operable for setting each preselectable delay time, each preselected delay time being set in response to an arrival time 2 The apparatus of claim 1 wherein a first one of said data signals comprises a clock signal 3 The apparatus of any preceding claim wherein said circuitry operable for setting each preselectable delay time comprises data compare logic operable for receiving a predetermined subset of said data signals, and outputtmg a first predetermined output signal value when said subset of data signals comprises a first predetermined set of values, and outputtmg a second predetermined output signal value when said subset of data signals has a second predetermined set of values, wherein said subset of data signals assumes one of said first and second predetermined sets of values response to said associated arrival times, and circuitry operable for modifying said preselected delay times response to said first and second predetermined output signal values 4 The apparatus of claim 3 wherein said first predetermined set of values comprises a set of values wherein each value is the same, and said second predetermined set of values comprises a set of values wherein a first member and a second member are different values 5 The apparatus of claim 3 wherein said circuitry operable for modifying said preselected delay times comprises a state machine operable for modifying said preselected delay times response to said first and second output signal values 6 The apparatus of claim 5 wherein said circuitry operable for modifying said preselected delay times furthei comprises a counter operable for receiving a direction signal from said state machine, said counter operable for outputtmg a count signal for determining a number of delay time increments for modifying said preselected delay times, wherein said delay time increment has a predetermined value . 7. The apparatus of claim 6 wherein said circuitry operable for modifying said preselected delay times further comprises delay control circuitry operable for receiving said count signal, and outputtmg a control signal to each of said plurality of delay devices, wherein said control signal is operable for modifying said preselected delay times. 8. The apparatus of claim 3 wherein said circuitry for modifying said preselected delay times in response to said first and second predetermined signals comprises: a storage device having an input coupled to said compare logic, a logic state of said storage device being operable for setting response to said first predetermined signal and resetting n response to said second predetermined signal; a counter coupled to said storage device operable for resetting said storage device after an elapse of a predetermined count; and circuitry operable for receiving said logic state of said storage device and modifying said preselected delay times m response to sa d logic state. 9. A method of dynamic wave-pipelining m an interface comprising the step of setting an arriving edge of each data signal of a plurality of data signals to correspond to an arriving edge of a latest arriving data signal said plurality of data signals. 10. The method of claim 9 further comprising the step of adjusting a clock phase wherein a predetermined transition of said clock is substantially centred a data window. 11. The method of claim 9 or 10 wherein said step of setting an arriving edge of said plurality of data signals comprises the steps of : determining said latest arriving data signal; and delaying each data signal by a preselected time delay, said preselected time delay being set response to a corresponding arrival time of each arriving edge. 12. The method of claim 11 wherein said step of determining said latest arriving data signal comprises the step of setting a predetermined transition of a clock signal to an arriving edge of said latest arriving data signal. 13. The method of claim 12 wherein said step of setting a predetermined transition of a clock signal to an arriving edge of said latest arriving data signal comprises the steps of : comparing sa d data signals, and outputtmg a first predetermined output signal value when said data signals comprise a first predetermined set of values, and outputtmg a second predetermined output signal value when sa d subset of data signals has a second predetermined set of values, wherein said subset of data signals assumes one of said first and second predetermined sets of values in response to said arrival times; delaying said clock signal by a predetermined delay time increment m response to said first output signal value; and repeating said comparing and delaying steps, wherein said step of repeating is terminated m response to said second output signal value. 14. The method of claim 11 wherein said step of delaying each data signal by a preselected time delay comprises the steps of. comparing said data signals, and outputtmg a first predetermined output signal value when said data signals comprise a first predetermined set of values, and outputtmg a second predetermined output signal value when sa d subset of data signals has a second predetermined set of values, wherein said subset of data signals assumes one of said first and second predetermined sets of values response to said arrival times; delaying a first data signal by a predetermined delay time increment m response to said first output signal value; repeating said comparing and delaying steps, wherein said step of repeating is terminated m response to said second output signal value; decrementing a delay of said first data signal by one delay time increment; and repeating said steps of comparing, delaying repeating and decrementing for a next data signal, wherein said step of repeating for a next data signal is terminated in response to a last data signal of said plurality of data signals. 15. The method of claim 9 wherein each data signal has a predetermined pattern of data values 16. The method of claim 10 wherein said step of adjusting said clock phase comprises the steps of . determining a late side of said data window, determining an early side of said data window, and setting a predetermined transition of said clock to an average of said early and late sides 17. The method of claim 16 wherein said step of determining said late side comprises the steps of : comparing said data signals, and outputtmg a first predetermined output signal value when said data signals comprise a first predetermined set of values, and outputtmg a second predetermined output signal value when said subset of data signals has a second predetermined set of values, wherein said subset of data signals assumes one of said first and second predetermined sets of values m response to sa d arrival times; delaying said clock signal by a predetermined delay time increment m response to said first output signal value; repeating said comparing and delaying steps, wherein said step of repeating is terminated m response to said second output signal value, and determining a data value representing a current delay time in response to said second output signal value, sa d data value representing said current delay corresponding to said late side 18 The method of claim 16 wherein said step of determining said early said comprises the steps of- comparing said data signals, and outputtmg a first predetermined output signal value when said data signals comprise a first predetermined set of values, and outputtmg a second predetermined output signal value when said subset of data signals has a second predetermined set of values, wherein said subset of data signals assumes one of sa d first and second predetermined sets of values m response to said arrival times, decrementing a delay time of said clock signal by a predetermined delay time increment m response to said first output signal value, repeating said comparing and decrementing steps, wherein said step of repeating is terminated in response to said second output signal value, and determining a data value representing a current delay time in response to said second output signal value, said data value representing said current delay corresponding to said early side. 19. The method of claim 17 wherein said data value representing said current delay time comprises a count. 20. The method of claim 18 wherein said data value representing said current delay time comprises a count. 21. A data processing system including an interface comprising: a central processing unit (CPU) ; a receiving device coupled to said CPU operable for receiving at least one data signal from said CPU, said receiving device including a data receive unit comprising: the interface apparatus of any claim 1-8.

Inventors: DREPS DANIEL MARK, FERRAIOLO FRANK DAVID, GOWER KEVIN CHARLES, DREPS, DANIEL, MARK, FERRAIOLO, FRANK, DAVID, GOWER, KEVIN, CHARLES
Applicants: IBM, IBM UK, IBM UNITED KINGDOM LIMITED, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 2000
Main classification: G06F13
IPC codes: G06F13, H04L7