SPI-4.2 dynamic implementation without additional phase locked loops
View Patent ↗A method and apparatus for receiving clocked data signals such as SPI-4.2 data signals is described. In one embodiment, each data signal lane is deskewed with respect to the clock by oversampling the signal on that lane, and considering multiple versions of a data sequence at different temporal offsets to the clock for correct reception of a training sequence. One of the temporal offsets is subsequently selected to provide the received bit sequence for that lane. Other embodiments are described and claimed.
1. A method of deskewing a data lane, the method comprising:
receiving a clock signal at a clock rate and a data signal driven at a data rate having an integral relationship to the clock rate;
sampling the data signal at a sample rate that is an integral multiple of the data rate;
for each of multiple temporal offsets, each offset from the clock signal by a corresponding offset based at least in part on an integer number of samples taken at the sample rate, comparing an expected bit sequence to a sequence of data signal samples taken at the corresponding offset, and offset from each other by a time period equal to the data rate; and
selecting, based on the comparison performed for each of the multiple temporal offsets, one of the temporal offsets as a data lane temporal offset for receiving the data signal.
2. The method of claim 1 , wherein selecting one of the temporal offsets comprises selecting, from among a group of the temporal offsets for which the expected bit sequence matches the sequence of data signal samples taken at those offsets, one of the group as an offset for the data lane.
3. The method of claim 2 , wherein selecting one of the group as an offset comprises selecting a range of temporal offsets that includes the group, and selecting the mean of the range as the data lane temporal offset.
4. The method of claim 1 , wherein comparing an expected bit sequence to a sequence of data signal samples taken at each of multiple offsets comprises feeding the sequence of data signals taken at each offset to a corresponding comparator for that offset, each such comparator outputting a result of the comparison for its corresponding offset.
5. The method of claim 4 , further comprising shifting samples taken at each given offset through a corresponding serial shift register chain shifted at the data rate, and supplying the output of the shift registers in the serial shift register chain to the corresponding comparator as the sequence of data signal samples.
6. The method of claim 5 , further comprising supplying the samples of the data signal taken at the sample rate to an input delay register of a delay multiplexer array comprising a plurality of serial delay registers including the input delay register, each delay register corresponding to one of the temporal offsets, and clocking the samples through the delay multiplexer array at the sample rate.
7. The method of claim 6 , wherein each serial shift register chain receives at an input the output of a corresponding one of the serial delay registers.
8. The method of claim 6 , wherein the delay multiplexer array receives a multiplexer select address indicating one of the serial delay registers corresponding to the selected data lane temporal offset, the delay multiplexer array supplying the output of the indicated serial delay register as the received data signal.
9. The method of claim 1 , wherein the method is performed concurrently for each of several data lanes to select data lane temporal offsets for each lane.
10. The method of claim 9 , further comprising detecting a recurring training sequence on the several data lanes, and repeating the method when the training sequence is detected.
11. A data receiver comprising:
a clock generator to receive a clock signal at a clock rate and generate a data clock at a data rate having an integral relationship to the clock rate, and a sample clock at a sample rate that is an integral multiple of the data rate; and
a first delay multiplexer array comprising a plurality of serial delay registers including an input delay register to receive a data signal, the delay multiplexer shifting samples of the data signal, taken at the sample rate, through the serial delay register at a shift rate equal to the sample rate, the delay multiplexer array further comprising a multiplexer select input to select one of the serial delay registers to provide samples of the data signal at the data rate, based on the data clock.
12. The data receiver of claim 11 , wherein the clock generator comprises a phase-locked loop locked to the clock signal.
13. The data receiver of claim 11 , further comprising a plurality of additional delay multiplexer arrays similar to the first delay multiplexer array, each delay multiplexer array receiving a corresponding one of a plurality of input data signals and supplying samples of that corresponding data signals at the data rate, based on the data clock and on a multiplexer select input to select one of the serial delay registers to provide the supplied samples.
14. The data receiver of claim 13 , further comprising deskew logic to provide the multiplexer select inputs to the delay multiplexer arrays.
15. The data receiver of claim 14 , wherein each delay multiplexer array provides comparison signals to the deskew logic, the comparison signals representing comparisons of a training sequence to a sequence of samples taken at the data rate and at a plurality of offsets to the data clock.
16. The data receiver of claim 15 , wherein the deskew logic chooses the multiplexer select input for each delay multiplexer array to correspond to a comparison at an offset for which the sequence of samples matches the training sequence.
17. The data receiver of claim 16 , wherein when multiple offsets produce a sequence of samples that match the training sequence, the deskew logic calculates a range of the multiple offsets and chooses the multiplexer select input to correspond to the mean of this range.
18. The data receiver of claim 15 , wherein each delay multiplexer array comprises a plurality of comparators, each outputting a comparison signal for a corresponding one of the offsets.
19. The data receiver of claim 18 , wherein each delay multiplexer array further comprises a plurality of serial shift register chains, each chain receiving samples at the data rate from a corresponding one of the serial delay registers and shifting the samples through the chain at the data rate, each chain supplying output from the serial shift registers in the chain to a corresponding one of the comparators.
20. The data receiver of claim 13 , wherein the receiver receives the clock signal and the input data signals as a DCLK and sixteen-lane DAT signals of a bus compliant with System Packet Interface Level 4 Phase 2.