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DS80PCI800: How does the part behave during Dynamic Link Equalization / training phases

Norman Wong5
Prodigy 210 points
Part Number: DS80PCI800
Other Parts Discussed in Thread: DS125BR820, , DS80PCI810

Hi all:

Could you explain how to properly use this repeater, especially during the training phase 0 to phase 3?

For example, during phase 1, if the EP device sends request on FIR setting to RC, would the repeater intercept and set its own Presets instead?  Or would it just pass the request upstream? If it only pass the information upstream, the EP would not see any differences in the signals as the repeater is the direct driver to the EP, not the RC device.  I saw from the datasheet that I could set the device to Gen3 mode through the I2C interface, and it is "transparent". I am not clear what this means. Also, if I have to manually tune the filters for deemphasis and equalization through the I2C interface, it seems to defeat the purpose of the training/recovery states. 

I am relatively new to PCIe Gen3. We are using this device to extend the reach and to combat losses in our design, but I am not certain if this could be done without some intervention through manual tuning.  Your help is much appreciated.

Norman

  • 0
    TI__Guru* 93670 points
    Hi Norman,
    DS80PCI800 would intercept and sets it's own presets instead. This device is a limiting device meaning it slices the signal and converts data to one or zero. On opposite side, we have linear devices. These devices are like analog buffer and they pass EP to RC signaling - device is seamless or transparent to these signaling. A device in this category is DS125BR820 device. Please take a look at specification for this device as well.
    Regards,,nasser
  • 0
    TI__Mastermind 43795 points

    Hi Norman,

    The DS80PCI800 and DS80PCI810 devices employ non-limiting output drivers.  This allows input analog waveform information in the form of Tx equalization from the RC and EP to pass through the redriver transparently.

    These parts are linear equalizers they do not participate in the digital protocol.  The equalizer settings will be static for the entire link training process.  This allows the EP and RC to compensate for attenuation which the DS80PCI800 or DS80PCI810 is not.  For this reason I recommend to set the CTLE gain functions at minimum levels and slowly increase the gain to determine the optimal redriver setting.  Starting with too much equalization can indeed cause issues with the link training process.

    To minimize manual tuning, I would recommend using the DS80PCI810.  In most cases I can give you a setting based on your system losses and equalizer placement which will work right away.

    Regards,

    Lee  

  • 0 in reply to Nasser Mohammadi
    Prodigy 210 points
    Hi Nasser:

    Thank you for the prompt response. According to the datasheet, the DS80PCI800 has programmable transmit de-emphasis. So it is not just a linear amplifier like the DS125BR820, correct? The DS80PCI800 has PCIe Gen3 mode which make this device attractive to us. However, it is still not clear to me how this device handle the training/negotiation. Does it take EP to RC request during phase 2, and set the downstream FIR setting, and at the same time, send another FIR setting request upstream to the RC? Will it then adjust the downstream equalizer based the data received from the RC. In phase 3, does it do the oppose? Could you clarify further? Thank you.
  • 0 in reply to Norman Wong5
    TI__Mastermind 43795 points
    Hi Norman,
    See my answer above. The best device to use in the DS80PCI810. It has passed PCI-SIG plugfest testing. It is the easiest to use and requires just minimum tuning.

    None of these devices will participate in link training in any way other than to pass through the Tx equalization waveforms using a non-limiting output drive. The DS80PCI810 has better linearity and this makes it less sensitive to placement location within the channel.

    Regards,
    Lee