Technical Seminar H412

Transcription

1 Technical Seminar H412 Nanosecond Impact on Hot-Swap Hank Herrmann - AMP Jack Kelly - Motorola Timothy R. Minnick - AMP 1

2 Nanosecond Discontinuities......are NOT pin bounce!!! 2

3 Session Outline of the Phenomenon 3

4 The Basic System Slot 1 Slot 2 Slot X Intense Error-Free Data Rates(telecom) Bus Architectures Conductive Interfaces (i.e. connectors) Hot-Swap Capability 4

5 The Hot-Swap System Hot-Swap Card Slot 1 Slot 2 Slot X Additional Energy Transfer Additional Signal Integrity Requirements 5

6 Motorola CPX8000 System Telecom Infrastructure Applications CompactPCI Architecture High Availability Data Intensive Device Redundant 6

7 Detection of a 7

8 Mechanical Connector Bounce Analyzed at birth of CPCI specification Typical speeds in microsecond range Pre-charge resistors Present signal integrity design can not respond to nanosecond discontinuities!! 8

9 Magnified 2mm HM Contact 9

10 Initial Test Set-Up 4.7k-Ohm Hot-Swap Card 5.0 V Scope Probe (1st Channel) Backplane Scope Probe (2nd Channel) GND 4.7k-Ohm Engagement Zoomed-inView (~40 usec) 10

11 Electrical 1K Standard Receptacle Standard Pin +5v V meas Oscilloscope Simple voltage divider Constant velocity fixture 11

12 Equipment References Detection Tektronix TDS 784A Digitizing Oscilloscope Motorola VxWorks Operating System Motorola CPX8000 Series Chassis & Cards Pin and Resistance Profiling Tektronix TDS 684A Digitizing Oscilloscope Mating Fixture with Pneumatic Drive 12

13 Test Set-Up Results Zoom-in Region 6.0 Voltage (V) Voltage (V) ns Time (usec) Time (usec) 13

14 - CPCI Network Hot-Swap Card 1.0 V 1.0 V Receiver 10k-Ohm 1.5" 10-Ohm 1.0 V Driver 10k-Ohm 1.5" 10k-Ohm 1.5" 10-Ohm 10-Ohm Slot 1 0.8" Slot 2 0.8" 0.8" Slot 8 14

15 of the 6.0 disengagement point Voltage (V) re-engagment point bus signal above receiver threshold Driver Card Hot-Swap Card Receiver Card Time (ns) 15

16 Summary A B C Receptacle Pin Initial point of contact - low normal force Highly conductive interface Microscopic irregularities 16

17 s => Nanosecond discontinuities => Energy transfer onto the bus => Signal Impact Any conductive hot-swap interface!! 17

18 s Software control during live insertion Decrease low normal force zone Limit rate of energy taken from the bus lower daughtercard capacitance physical restructuring impact on signal integrity and timing add resistance during engagement 18

19 Resistive Pin Development Unmated Receptacle and Pin Resistive Coating A B C D E Receptacle Pin Sufficient Normal Force Engagement Position A B C D E Receptacle Pin 19

20 Isolation-to-Resistive Transition 6.00 disengagement point 5.00 re-engagement point Driver Card Hot-Swap Card 4.00 Receiver Card 3.00 gradual release onto backplane Voltage (V) acceptable level Time (ns) 20

21 Electrical Verification +5v V DC R 1 1K V meas Standard Receptacle R tip Oscilloscope Resistive Tip Pin R tip = V V meas dc -V R 1 meas 21

22 Resistance Profile Cycle #1 Cycle #100 Resistance (kohms) Ohm max Ohm min Time (msec) 22

23 Mechanical Different Lighting on Magnified Pin Engagement Cycles High-cycle durability Exceptional adhesion to gold Absence of debris 23

24 2mm HM product spec ( ) 250 cycle durability pin staging Bellcore GR-1217-CORE (Telcordia( Telcordia) Resistance requirements 24

25 - The Problem 6.0 disengagement point 5.0 re-engagment point Driver Card Hot-Swap Card bus signal above receiver threshold Receiver Card Voltage (V) Time (ns) 25

26 - The 6.00 disengagement point 5.00 re-engagement point Driver Card Hot-Swap Card 4.00 Receiver Card 3.00 gradual release onto backplane Voltage (V) acceptable level Time (ns) 26

27 - The Connector 27

28 The Quiet Mate TM Contact 28

29 3.3V CPCI System disengagement point re-engagement Receiver Card Hot-Swap Card Driver Card bus signal above receiver threshold Voltage (V) Time (ns) 29

30 3.3V Quiet Mate TM CPCI System disengagement point re-engagement point Driver Card Receiver Card Hot-Swap Card gradual release onto backplane Voltage (V) acceptable level Time (ns) 30

31 Nanosecond Discontinuities & Quiet Mate TM Contacts The Quiet Mate TM Contact irregularities and the relative motion of the structures at the near-zero normal force area of engagement. Nanosecond discontinuities are different from pin bounce, in that they are not a mechanical deflection and return of the contact beam, but rather a result of the relative motion and initial contact of the conductive interface. 1 February 10, 2000 Measured Nanosecond Discontinuties?? Initial Contact Point - Low Normal Force Microscopic Irregularities Highly-Conductive Interface A B C Voltage (V) 6.0 Zoom-in Region Time (usec) Voltage (V) ns Time (usec) 3 February 10, 2000 Receptacle Different From Pin Bounce Pin 2 February 10, 2000 Telecommunications equipment continues to drive faster and faster data rates and bandwidths (levels approaching 1Tbps). These high-speed systems must be extremely reliable and demand that the data they process meets this level of reliability (five 9 s). Bus-type architectures, including CompactPCI, provide the backbone for such systems. Therefore, bused signal systems operating within these requirements must also assure that the data they carry is error free, even during live insertion operations. During the development and testing of these systems, nanosecond discontinuities were discovered with repeatability. Nanosecond discontinuities are electrical connects/disconnects occurring in the arena of several nanoseconds to tens and hundreds of microseconds. The electrical disruption resulting from these intermittencies can adversely affect certain systems. Nanosecond discontinuities occur at the initial point of closure between two highly conductive separable interfaces. It is primarily a result of the microscopic Nanosecond discontinuities are extremely difficult to capture with consistency. An extensive understanding of the system and how it responds to a live insertion event is critical in detecting the phenomenon. Advanced (and expensive) test probes, measurement scopes, and specialized test fixtures aid in the identification of the intermittencies. Data samples from one such test set-up are clear enough to discern the faster disruptions, due to the optimally reduced time constant of the test-bed. The measured waveforms were plotted on a voltage scale to 5V against a physical engagement timescale. The recorded data is then focused on the specific areas around the transition edges of engagement and disengagement. The measured waveform displays intermittencies detected during a card engagement event. When the irregularities are magnified [seen as the waveform on the right], a discontinuity of approximately 44 nanoseconds is measured. The intermittencies are extremely erratic and vary anywhere from 100 s of microseconds to single digit nanoseconds. The 1 04/20/00

32 Nanosecond Discontinuities & Quiet Mate TM Contacts phenomenon has been detected during both engagement and disengagement operations. Susceptible Systems Slot 1 Hot-Swap Card Slot 2 Slot X Bus Architectures Hot-Swap Capability High Fault-Tolerance Requirements 4 February 10, 2000 Specific systems which are susceptible to nanosecond discontinuities are those which have a bused or multi-drop architecture, and possess the capability of hot-swapping cards. An operating system requires that at least one card is present and driving, with a second (or additional) card(s) receiving, when a third card is inserted into the system. Typically, systems which require high faulttolerance operation will be more affected by nanosecond discontinuities (as the intermittencies tend to adversely impact systems on a relatively infrequent basis). - At the first break point (or beginning of the nanosecond discontinuity), the hot-swap card electrically separates from the running bus, and continues to hold the energy it had when the separation occurred. This energy will leak off as a result of pre-charge or other termination devices, but it is typically subject to extremely slow time constants, as a result of the high resistance value associated with pre-charge elements. - During the nanosecond discontinuity event, the backplane bus may switch logic levels (in the example, the bus transitions from high to low). High-speed drivers will allow this transition to occur as quickly as 1-2 nanoseconds, or possibly faster. - Shortly after the bus transition, the nanosecond discontinuity ends, and the hotswap card comes back in electrical contact with the backplane bus. Two separate voltage potentials come together at one point. - As a result, energy will immediately be transferred to/from the daughtercard, depending on relative potentials. This energy transfer has the capability of impacting a received/sampled signal waveform significantly enough to result in false data transfer. Hot-Swap System Diagram Detection of the 6.0 disengagement point Bus Driver Data Transition re-engagment point Driver Card Hot-Swap Card Receiver Card Receiver Card Hot-Swap Card Pre-Charge Established Nanosecond Event Voltage (V) bus signal above receiver threshold 0.0 1st Contact 1st Break 2nd Contact Time (ns) 5 February 10, February 10, 2000 A simple timing diagram best illustrates the worst-case impact of a nanosecond discontinuity: - At first contact between a hot-swap card and the backplane, all waveforms coincide (including the hot-plugged card), as all pieces are connected electrically and running. An actual system waveform plot displays the impact of a nanosecond discontinuity on a sampled waveform. The additional transferred energy boosts the level of the signal above the threshold of the receiver (blue line), and could result in a false sampling of data. 2 04/20/00

33 Nanosecond Discontinuities & Quiet Mate TM Contacts Nanosecond Impact => Nanosecond discontinuities => Energy transfer onto the bus => Signal Impact Any conductive hot-swap interface!! 7 February 10, 2000 and testing of hot-swap networks has shown that nanosecond discontinuities result in energy transferred onto or out of the bus. Additional energy transferred to an active bus has the potential of altering signal levels. (Existing pull-up terminations are ineffective during a nanosecond discontinuity, due to their relatively slow time constants.) Nanosecond discontinuities can occur at any conductive hot-swap interface at the near-zero normal force zone that occurs at the very beginning of engagement. s Software control during live insertion Decrease low normal force zone Limit rate of energy taken from the bus lower daughtercard capacitance physical restructuring impact on signal integrity and timing add resistance during engagement the amount of time that the phenomenon can exist and would reduce the probabilities of a system detecting discontinuities. However, since there is always an initial point of contact, and since the inconsistencies occur on the molecular level, probabilities are decreased but not eliminated. The final option is to limit the amount of energy the daughtercard injects/absorbs to/from the bus when the two metal surfaces make electrical contact. One way of approaching this is to lower the capacitance on the daughtercard as much as possible. Minimization of contact pads and other metallic structures will reduce this capacitance and effectively make the daughtercard more inductive. However, this reduction in capacitance can have an illeffect on the loading and timing of the bus, especially since the reduction must occur on all cards. In addition to signal integrity concerns, the reduction in capacitance still may not guarantee that the energy flow will be reduced to an acceptable level. The second option to reducing energy flow during the mating sequence is to create a resistive shock absorber between the receptacle contact and the header pin, until an acceptable normal force can be established. This resistance would then be invisible to an operating system (following the live insertion event). Resistive Application Unmated Receptacle and Pin Resistive Coating 8 February 10, 2000 Receptacle Pin s to nanosecond discontinuities can take several forms. The situation can be controlled through software or hardware. Software solutions are possible, but slow the overall response of the system, thus a hardware solution that does not slow the system is preferred. A decrease in the time of low normal force mating would help to minimize discontinuities. Stiffening backplanes and pre-loading spring members help to decrease Receptacle Final Engagement Position Pin 9 February 10, 2000 The requirement of a guaranteed error-free live insertion points to the application of a resistive material on the pin as the best solution. The material must exist on a specific region of the pin. The material 3 04/20/00

34 Nanosecond Discontinuities & Quiet Mate TM Contacts must exist on the tip of the pin in any area where the pin and receptacle could possibly make first contact. The material must also extend back far enough on the pin to assure that sufficient normal force is obtained prior to the receptacle sliding to and making definitive contact with the gold surface of the pin. Sufficient normal force guarantees that the receptacle contact will not lose electrical contact with the resistive material or gold finish. The final resting position of the pin is noted by the vertical dashed line. System Diagram Improved Electrical simulations provide waveforms showing an actual bus signal s response to a live insertion event, with the resistive material present on the tip of the pin. The resulting rate of current into the backplane network is not enough to force the continuously running data bus to cross the thresholds of the detecting receiver. 2mm HM product spec ( ) 250 cycle durability pin staging Bellcore GR-1217-CORE (Telcordia( Telcordia) Mixed Flowing Gas (MFG) Temperature/Humidity Bus Driver Receiver Card & Quiet Mate Contacts Data Transition Resistance requirements Hot-Swap Card Pre-Charge Established Nanosecond Event 12 February 10, 2000 Hot-Swap Card & Quiet Mate Contacts 1st Contact 1st Break 2nd Contact 10 February 10, 2000 An adjusted timing diagram displays the new behavior of a hot-swapped card, and the resulting energy response seen at the input of a sampling receiver device, when the resistive pin tip is used. The total amount of energy transferred is the same as before, however the rate at which it is transferred is much different. The reduced transfer rate provides an impact at the receiver that no longer can result in a false sampling of the waveform data. The new resistive material has been tested to the 2mm HM product specification ( ) and qualified to the Bellcore GR CORE (Telcordia) specification. The pin continues to meet all specifications. The durability of the new material exceeds the already high (250 cycle) product requirement. Pin staging requirements continue to provide sequential mating, due to the location of the resistive material. The material is also being qualified, through resistance profiles, to the required resistance ranges specified by the simulations and verification testing. The 6.00 disengagement point 5.00 re-engagement point Driver Card Hot-Swap Card 4.00 Receiver Card 3.00 gradual release onto backplane Voltage (V) acceptable level Time (ns) 11 February 10, /20/00