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DS320PR1601: eye diagram test fail

Jeff YANG
Genius 5895 points
Part Number: DS320PR1601
Other Parts Discussed in Thread: DS160PR1601

Hi,

As below, I am verifying my re-driver card using TI DS320PR1601.

Use default value , I can link at Gen5 but bad eye-diagram .

I need your help to teach us how to set the best values. thanks!

  • 0
    Genius 5895 points

    Hi,

    I try to access register (address 0x81& 0x83) to exchange gain value, I have tried many combinations but it doesn’t work
    I want to ask some question
    Q1: I find the example in spec (pic1) ,the gain of 0b on all channels should be <i2c_write addr="0x18" > 81 80 </i2c_write>,why the value in spec is 0x98?
    I set EQ index that gain 9 (0x81 register value is 0x20)( (0x83 register value is 0x1d)) is that correct?

    Q2: when I use microchip to set the value , I need to reset Broadcom switch or not ? it can link train by itself or not?

    Jeff

  • 0 in reply to Jeff YANG
    TI__Genius 13135 points

    Hi Jeff,

    Jeff YANG said:
    Q1: I find the example in spec (pic1) ,the gain of 0b on all channels should be <i2c_write addr="0x18" > 81 80 </i2c_write>,why the value in spec is 0x98?

    The example you posted is showing how to set the device settings with EQ 2 and flat/DC gain of 0 dB. The 0x98 value assigned to channel register 0x81 sets the EQ/CTLE setting to Index 2. Writing register 0x81 with a value of 0x80 will set EQ to Index 0 instead.

    This table is from the DS160PR1601 and DS320PR1601 Programming Guide. Generally, the EQ index is the most important parameter to adjust, DC gain is secondary. The boost provided by the Default EQ setting is approximately between EQ 4 and EQ 5. You may try increasing the EQ in small steps of 6, 7, etc. and observe the effects on the eye diagram.

    Jeff YANG said:
    I set EQ index that gain 9 (0x81 register value is 0x20)( (0x83 register value is 0x1d)) is that correct?

    These register values lead to EQ 9 and DC gain of 0 dB.

    Jeff YANG said:
    Q2: when I use microchip to set the value , I need to reset Broadcom switch or not ? it can link train by itself or not?

    When the redriver settings are changed, the link should be retrained or warm reset so that the CPU and endpoint can reoptimize their PCIe presets and other internal settings.

    Best,

    Evan Su

  • +1 in reply to Jeff YANG
    TI__Genius 16721 points

    Hi Jeff,

    Regarding DS320PR1601 SMBus programming, EQ Index is selected by writing portions of both 0x81 and 0x83 (for all channels).

    To set the Flat Gain/DC Gain to 0dB for all channels of the bank, write 0x83[2:0] = 0x5 (with appropriate mask of 0x7). Bits 6:3 in this register control another portion of EQ Index. To set the EQ Index for all channels of the bank, write 0x83[6:3] and 0x81[7:0] with the appropriate values.

    Here are a couple of examples - please refer to the programming guide for all examples:

    EQ Index (all bank channels) DC Gain (all bank channels) Reg. 0x81 Reg. 0x83
    0 0dB (Default) 0x80 0x05
    0 -2dB 0x80 0x03
    0 -4dB 0x80 0x01
    0 -6dB 0x80 0x00
    0 +2dB 0x80 0x07
    1 0dB (Default) 0x88 0x05
    2 0dB (Default) 0x98 0x05
    Default 0dB (Default) 0x00 0x05
    5 0dB (Default) 0x00 0x0D
    6 0dB (Default) 0x08 0x0D

    Regarding EQ programming and the PCIe link - the PCIe link should be retrained if EQ is adjusted on the DS320PR1601, as this will re-initialize the PCIe link training process for PCIe root complex and endpoint in the link. My understanding is that the BRCM switch should have an -SBR mechanism to retrain the link via command line. I believe this would be outlined in some of the BRCM documentation.

    Could you please elaborate on the following to help us better understand the setup.

    • Which BRCM device is being used (as root complex)?
    • Which endpoint is being used?
    • Any further details on the configuration (loss, block diagram)?

    Best,
    David

  • 0 in reply to David Waier
    TI__Genius 16721 points

    Hi Jeff,

    I'm marking this case as resolved due to inactivity. Please let us know if you have any further questions.

    Best,
    David

  • 0 in reply to David Waier
    Genius 5895 points

    Hi David,

    After the setup is completed, the change in the eye diagram is minimal. Although there is a slight improvement, the effect is not significant. We have made our own passive card (a simple riser card) and looped it back. The signal from station 2 is connected to the passive card, looped back to station 3, and the signal remains intact. However, when the re-driver card is connected, the effect is limited regardless of how it is adjusted.

    The waveform generated from our configured index shows that index 13 is the best, but its gain can only increase by up to 2dB. There are very few waveforms with open eyes when adjusting the index, and even with an additional 2dB gain, the effect does not seem significant. The figure1 is the graph of index 13 with gain set to 0. The second image is the eye diagram drawn using the loop back method mentioned in above.

  • 0 in reply to Jeff YANG
    TI__Genius 16721 points

    Hi Jeff,

    You've stated that few EQ settings seem to open the eye diagram - have you tried low EQ boost settings like EQ Index 0 or EQ Index 1?

    Additionally, could you please elaborate further on the insertion loss in your configuration so that we can help to better make recommendations for EQ settings?

    Best,
    David