Sierra MC7455 mPCIE on Solidrun Clearfog board

IoT Modules MC/EM Series
1

Hi,

I am currently trying to get a Sierra MC7455 Wireless Adapter working on my clearfog device (Clearfog-A1 Rev 2.1) using the mPCIE port. I have an SSD plugged into the other mPCIE port and when altering the configuration can see that without issue in u-boot and the OS.

However, I can not see the Sierra card from either u-boot or OS, in fact, in u-boot i see this message all the time:

PCI-e 0: Detected No Link.

I have read that the Sierra card is “seen” as a USB device in other OS’s, but can this be used on the clearfog board? I know the mPCIE port can be changed to be mSATA from within u-boot ( as I have already done this for the SSD drive), but is there anything special I need to do to enable it to act as USB, if it can in fact be done. Perhaps I should use the M.2 version of the Sierra card rather than mPCIE

I have seen this thread on the forums here : "https://forum.sierrawireless.com/t/mc7455-breaks-mini-pcie-standard/8511/1 and not sure if it relevant, but it is about the Sierra card uses a different standard and needs some pin’s covered to work correctly.

Thanks in advance,
Nigel.

2

Yes, you need to cover the 4 pins used for the PCIe TX and RX differential pairs. Your mini-PCIe slot is wired for USB2 and PCIe x1. This is according to the original minicard pinout. The MC7455 uses a new alternate pinout, where the PCIe x1 pairs have been repurposed for USB3 . This confuses the PCIe system. Covering the pins will let the module use the USB2 link.

As discussed in that thread, you may theoretically have to cover some of the other pins too. But in my experience, the only ones causing trouble are the TX/RX pairs. And as noted there: Those 4 pins are located next to each other, only separated by 2 redundant ground pins, so you can just cover all 6 with a single piece of tape.

3

Hi,

I think this can be fixed by changing the SERDES MUX in Clearfog pro.

There are few SERDES mux options and just looked on Clearfog pro and you can configure SERDES number 4 from pcie to USB host 0.
USB host 0 SERDES with USB 2.0 number DM1/DP1 will become a full USB 3.0 that you can use.

If the new addition to the standard keeps the USB 3.0 serial capacitors as in pcie then this should work without issues.
So, you need to do the following -

  1. First use CON2 mini pcie connector; that’s the one in the middle of the board and not near the DC jack.
  2. Modify u-boot instead of PEX2 to USB3_HOST0 and instead of PEX_ROOT_COMPLEX_x1 to SERDES_DEFAULT_MODE - github.com/SolidRun/u-boot-arma … -38x.c#L99
  3. I’m not sure which kernel you are using, but make sure that the first USB3.0 is enabled in the kernel device tree.

Let me know how it goes.

Regards,
Rabeeh

4

Would there be similar solution for Hummingboard2 Gate?

Regards,
Sebastian