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MIPI DevCon 2016: Versatile Software Solution for MIPI C-PHY TX Testing

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C-PHY has emerged as an interface alternative to D-PHY in MIPI camera applications. By decreasing toggle rate and increasing bandwidth, C-PHY offers systems designers more options for controlling EMI and power within a system, while maintaining high performance. However, testing C-PHY presents unique challenges, due to the need to monitor 3 lines simultaneously, as well as unique encoding and decoding methods. To address these challenges, UNH-IOL has created the C-PHY GUI tool. Similar to the widely used D-PHY GUI tool, C-PHY-GUI interfaces with oscilloscopes from various vendors. In this presentation, Paul Willis of UNH-IOL discusses the methodology behind C-PHY GUI, the challenges of building and testing it, and how to use it to easily test a C-PHY implementation.

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MIPI DevCon 2016: Versatile Software Solution for MIPI C-PHY TX Testing

  1. 1. Versatile Software Solution for MIPI C-PHY TX Testing Paul Willis UNH-IOL
  2. 2. Contents •  Who is the UNH-IOL? •  C-PHY TX Testing Tool Overview •  Physical Test Setup •  Clock and Data Recovery •  HS Packet Decode •  HS TX tests 2
  3. 3. UNH-IOL • MIPI Member since 2007 • Helped develop D-PHY Test Suite • Authored DPHYGUI Test Tool • Active test house for MIPI CSI, MIPI DSI, and MIPI D-PHY • Active in the Test Work Group • Work with several other Organizations to develop new technologies • Employ 100 university students 3
  4. 4. Testing MIPI C-PHY TX • Address issue of missing reference platform for performing C-PHY CTS TX tests • The industry has need for this software • Will be available for purchase to MIPI members • Meant to complement oscilloscope software package offerings 4
  5. 5. CPHYGUI Overview • MATLAB based software measurement tool • Evaluate PHY TX characteristics • Capture, import, and process waveforms •  Can download captures or import saved waveform files from Tektronix, Keysight, LeCroy, and Rhode & Schwarz oscilloscopes • Decode HS packets and LP sequences • Display and manage measurement results in GUI • Load/save measurement results • Command Line Interface 5
  6. 6. CPHYGUI 6
  7. 7. Test Setup 7 •  Real time oscilloscope •  High impedance probes •  C-PHY Reference Termination Board •  RTB may be used as probing point with probe tips soldered to the board DUT (P339) Probing Point C-PHY RTB Oscilloscope Computer CPHYGUI Da A/B/C Da A/B/C Ch 1/2/3 Da A/B/C GPIB / Ethernet
  8. 8. Clock and Data Recovery •  Lowpass filter data •  Find differential edge times •  Throw out edges from out of spec UI (too long/short) •  Find mode of UI length •  Run second pass using previously estimated UI length 8
  9. 9. Decoder •  Byte level decode of HS burst packets •  Protocol aware (CSI-2 and DSI) planned •  LP decoder planned •  Output to console •  Option to save log to text file 9
  10. 10. HS-TX Tests •  Capture from oscilloscope or import from file •  Sample rate above 5 GS/s and burst length of at least 5 thousand symbols suggested. •  Cropped single burst: 10
  11. 11. TLPX, T3-PREPARE, T3-PREAMBLE, and T3-SYNC •  HS entry timers measured as described in CTS •  TLPX: Time between VA and VC crossing VIL,MAX (550 mV). •  T3-PREPARE: Time between end of TLPX and HS-0 (+/- 40 mV). •  T3-PREAMBLE: Verifies length of preamble (in place of following tests). •  T3-PREBEGIN/T3-PROGSEQ/T3-PREEND: To be implemented. •  T3-SYNC: verify sync word (3,4,4,4,4,4,4,3) after preamble 11
  12. 12. VOD (max strong, min weak HS-0 and HS-1) •  Eye based measurements performed on all three differential pairs (VOD-AB, VOD-BC, VOD-CA) •  Measured at -20% of UI •  Calculate ΔVOD by subtracting absolute value of maximum strong 1 from absolute value of strong 0. •  Take highest value from all three differential pairs 12
  13. 13. VOHHS •  Mean of single ended waveform taken at -20% of UI •  Applicable to all 3 single ended lines 13
  14. 14. VCPTX and ΔVCPTX(HS) •  14
  15. 15. T3-POST •  Verify that the last 7 symbols in the burst are the “4” symbol 15

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