SMBus connectivity on PCIe slots

  • Hi,

    Are the SMBus pins on the PCIe connectors on the carrier connected to either the BMC or the main processor on the systems? GPUs and other cards often expose out of band temperature monitoring, etc, over that interface so it would be useful to have available.


    The block diagram is not showing the connectivity, but it's also just a high-level capture.

  • @Olof Johansson Assuming it was strictly followed, I wonder if the PICMG COM-HPC Design Guide might be any use?

  • @Olof Johansson 


    Hi Olof,


    There the SMBus has route bewteen PCIe and BMC, but for application as fecthing of temperatures information...etc, before command executing by BMC, you would need to figure out what registers information you need and can get first about the connected PCIe devices (Graphic..etc), and BMC can just executing with accurately parameters, fetching the information/registers you need throught SMBus.

    If you can get some datasheet of the specifc PCIe devices, sharing with us, then I would try to provide some more information for you late as possible.

  • Schematics of the COM HPC carrier can be found on this page

    it explains any connection from PCIe to BMC

    As a side note : we still do not have full functionallity on the BMC  specially using ipmitool but this will be solved soon I epxect by an update of the BMC firmware. Currently the only route from SOC to BMC is through the MMC on the module but this architecture has limitations specially on the command set. Since MMC uses UART to SOC you need "serial commands" There is also a connection from Altra SOC through I2C9 to the BMC we have this working in lab settings but it needs a little more time before we will release that one. 

    So as Lauryn says if you have an PCIe add on device in mind already share it with us and we have a look how to retrieve data from it.


  • Ah, thanks for the pointer to the schematics. So it looks like the slots are all chained to the BMC SMBUS, that's promising.

    As far as the HW specifics go for the cards I'd like to monitor -- I have access to all of the needed specs, but I'll experiment a bit at my end before I share more.

  • @Ruler of COM Thanks! In this case I'd be happy just being able to probe the bus manually with i2c-tools on the BMC to start. I'm more interested in OOB/redfish interface than inline to the host anyway.


    Now I just need to wait for my board to clear customs and actually get delivered. :)

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