Hi,

We are using Rambutan module in our design. We have designed schematic for PCIe as given in the reference design on the web.

U-boot on the board is working but we are not observing 100MHz differential on pin 16 and pin 17 (PCIE_CLK_N and PCIE_CLK_P) on the Rambutan module.

We have even isolated series resistors on differential lines but still clock is not coming out from the module properly. Some 112KHz is seen and which is also not very good.

(In U-boot internal radio seems to get detected though).

Could you suggest what could be the problem.

thanks.

Amit.

Hi Amit,

Did you have any luck with the PCIe bus on the Rambutan board? I have also followed the design schematic but the resulting slot is not operational and no (mini)PCIe cards are detected. Any information you have been able to gather would be much appreciated.

Regards,

Ross

Hi Gedass,

Thanks for the pointer! How do I change the PCI bus mode? I can see the DIP switch in the schematic but it is confusing as in one diagram GPIO12 goes to GND via 10K resistor but then it also goes to 2V5 via the DIP switch and a 1K resistor. Which is the correct method to set the PCIe bus mode?

Regards,

Ross

Hi,

GPIO12 - "0" PCIE EP mode, "1" PCIE RC mode
GPIO13 - USB_MODE ( "0" Host mode, "1" Device mode )

So you need GPIO12 to 2.5V via resistor.

Hi Gedass,

Thanks again for the help. I've tried raising GPIO12 with 2.5v (confirmed with /sys/class/gpio/gpio12/value) but the PCIe slot is still not detecting cards (Ath9k wireless). Is there any chance you could have a look at our PCB schema and see if you can see what the problem might be (if physical)?


Ross

Have you tried a pci-e 1.1 device? Because I have kind of the same problem with pci-e 2.0 cards.

Herman