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DS80PCI402: Configure from SMBUS

Yong Yang
Prodigy 20 points
Part Number: DS80PCI402

Tool/software:

Hi, Dear supporter,

    I am using DS80PCI402 to boost a 2x PCIe connection. If I using pin mode, set pin state as following, the EP device can be enumberated by host.

 

ENSMB

1K to GND

EQA[1:0]

1K to GND, 1K to GND

EQB[1:0]

1K to GND, 1K to VIN

DEMA[1:0]

Float, Float

DEMB[1:0]

Float, Float

LPBK

Float

VDD_SEL

GND

SD_TH

Float

/PRSNT

LOW

VIN

3.3V

 Then I tied ENSMB to VIN to access the device from SMBUS, according to the table above, I set,

EQA0/1  = 0x00

EQB0/1  = 0x03

DEMA0/1 = 0x02

DEMB0/1 = 0x02

VOD =  0x05

However, the EP cannot be enumberated by host.  Therefore,

1) Is there a way to read registers out by SMBUS when chip is in PIN mode? If yes, I can read the configuration out in PIN mode as a starting point for SMBUS mode.

2) I've provide the register dump and schematic as below, could you please help to analyze? 

Data read from device:
0000: 40 00 00 00 00 00 10 01 00 00 cc 70 00 00 08 03
0010: ad a2 00 00 00 08 03 ad 82 00 00 00 00 2f ad 02
0020: 00 00 00 00 2f ad 02 00 0c 00 00 08 00 ad e2 00
0030: 00 00 08 00 ad e2 00 00 00 00 2f ad 02 00 00 00
0040: 00 2f ad 02 00 00 38 00 05 00 00 00 00 00 00 00
0050: 00 44 00 00 00 00 10 44 21 00 54 54 00 00 00 00

  • 0
    TI__Mastermind 23655 points

    Hi Yong,

    Your pin mode to register value conversion is correct.

    Unfortunately it's not possible to access registers in pin mode.

    I'll need some additional time to review your register dump and schematic. I'll get back to you with more feedback early next week.

    Best,

    Lucas

  • 0 in reply to Lucas Wolter
    Prodigy 20 points

    Hi, Lucas, 

        After re-check the datasheet, I forget to set bit 3 of register 0x06. After set it to 1, I can achieve similiar behavior as pin mode. I have another PCIe slot which is farther from CPU and PCIe card cannot be detected in this slot. As the distance increased, for EQ/VOD/DEM registers on host side, Should I increase/decrease each parameters to try?

  • 0 in reply to Yong Yang
    TI__Mastermind 23655 points

    Hi Yong,

    I'm glad you were able to resolve the issue.

    You will likely need to increase the EQ setting to support a longer channel. It's difficult to say how VOD and DEM need to be adjusted without manually tuning these parameters.

    Do you have an estimate for insertion loss? This can serve as a good starting point to tune EQ.

    • EQ (continuous time linear equalizer):  This is the primary RX equalization block. Boost is applied at the redriver receiver to compensate for insertion loss on the RX channel. Boost levels are given in Table 8-2 in the datasheet. I recommend tuning this parameter first.
      • If you have a measure/estimate of the insertion loss on the RX side of each channel, you can start with an EQ level with matching boost. Step the EQ level up/down until the best eye diagram is observed.
      • If you do not have a measure/estimate of insertion loss, you can start with minimum EQ setting. Step the EQ level up until the best eye diagram is observed.
    • DEM (de-emphasis): This is the primary TX equalization block. The signal is attenuated as a form of pre-distortion to improve eye opening at a downstream receiver. De-emphasis levels are given in Table 8-3 in the datasheet. I recommend tuning this parameter after EQ. High de-emphasis settings may impact link training pass through performance.
      • Start with DEM=0 setting. Step the DEM level up until the best eye diagram is observed.
      • If you are using Gen3 mode (RATE pin is pulled low with 20k resistor), de-emphasis is disabled.
    • VOD (differential output voltage): This is the primary output amplitude control. In Gen3 mode, the redriver maintains signal chain linearity. This means the output amplitude will track the input amplitude and the VOD values shown in Table 3 are not maintained for all input amplitude levels. I recommend tuning this parameter last, and using a setting of 1V or higher if you are using Gen3 mode.
      • VOD setting will likely have minimal impact on eye opening.

    Best,

    Lucas