Hi Zheng, Schematic is simple and OK. I assume you are trying to run Wolf VPXxx-E8860-xxxx or similar GPU borad. You can't do much there if there is a hardware problem but it is most possibly a software setup problem.
VPX does not have incomming clock so it is by default in async_clock mode. The question is did you allowed that mode on the main board side? Asynchronous clock mode is not default mode for a motherboard. Check if the mode is allowed. Second, check if the other PCIe device can work on the motherboard PCIe slot. Regards, Predrag On Fri, Jan 13, 2017 at 6:44 AM, Zheng Bao <fishb...@hotmail.com> wrote: > Here is the ref clk part. Please review. > > No refclk routes to VPX connector. > > > Thanks. > > > Zheng > ------------------------------ > *From:* Predrag Vidic <pvi...@gmail.com> > *Sent:* Thursday, January 12, 2017 6:53 PM > *To:* Zheng Bao > *Cc:* Zoran Stojsavljevic; firstname.lastname@example.org > > *Subject:* Re: [coreboot] Question about PCIe separate reference clock > > Hi Zheng, > > Without knowing the particular solution for the PCIe transmitter you have > on your board, I'd check refclk pins on your design for the proper > termination. The problem can be in irregular readings from the pins. > > Reragds, > Predrag > > On Thu, Jan 12, 2017 at 3:26 PM, Zheng Bao <fishb...@hotmail.com> wrote: > >> Q: do you use local xtal attached to Si52111-B5 to generate local PCIe >> 25MHz clock? >> >> Zheng: yes >> >> >> Q: If you dothis, my next question is how you synchronize these two >> clocks: Local >> PCIe 25 MHz and common reference clock from CPU? >> >> Zheng: We do NOT sync these two. >> >> >> Q: Since these two clocks, as I understand above scenario, are >> asynchronous to each other?! >> >> Zheng: yes. Asynchronous. >> >> >> The VPX connector does not have a PCIe ref clock signal, so we can not >> send CPU PCIe ref clock to >> >> device. The PCIe spec says if the separate refclk on devices should be >> 100MHz ± 300PPM, with SSC >> >> off. We believe our board meet this requirement. So we doubt the problem >> lies in PCI configration space. >> >> >> Zheng >> >> >> >> ------------------------------ >> *From:* Zoran Stojsavljevic <zoran.stojsavlje...@gmail.com> >> *Sent:* Thursday, January 12, 2017 9:22 AM >> *To:* Zheng Bao; Predrag Vidic >> *Cc:* email@example.com >> *Subject:* Re: [coreboot] Question about PCIe separate reference clock >> >> Hello Zheng, >> >> For decades, I've been FW/SW engineer, but I do understand a little >> bit of a HW. I have looked into the Si52111-B5 data sheet for >> clarification. >> >> My problem here is to understand, your use case: do you use local xtal >> attached to Si52111-B5 to generate local PCIe 25MHz clock? If you do >> this, my next question is how you synchronize these two clocks: Local >> PCIe 25 MHz and common reference clock from CPU? >> >> Since these two clocks, as I understand above scenario, are >> asynchronous to each other?! >> >> Please, clarify for us your use case. >> >> Thank you, >> Zoran >> _______ >> >> On 1/12/17, Zheng Bao <fishb...@hotmail.com> wrote: >> > Our VPX design uses separate reference clock source, which is >> Si52111-B5 (No >> > spread), instead of common ref clock from CPU. >> > Now The system is unstable. Reading PCIE configuration space is unstable >> > too. (If we add some fly wire to make it work with common ref clock, the >> > system becomes stable.) >> > >> > (abstracted from PCIe spec: 12 Slot Clock Configuration - This bit >> indicates >> > that the >> > component uses the same physical reference clock that the >> > platform provides on the connector. If the device uses an >> > independent clock irrespective of the presence of a reference >> > clock on the connector, this bit must be clear. >> > For a multi-Function device, each Function must report the >> > same value for this bit.) >> > >> > Based on my understanding, the BIOS need to read bit "Slot Clock >> > Configurationclear" to see if >> > separate ref clock is used. BIOS then write bit "Common Clock >> > Configuration". >> > >> > On our board, the bit "Slot Clock Configuration" is always 1, which I >> assume >> > should be 0. >> > >> > My question is, how the hardware affect the bit "Slot Clock >> Configuration"? >> > How do we need to design our board to make the bit "Slot Clock >> > Configuration" be 0? >> > >> > Thanks. >> > >> > Zheng >> > >> > >> > >
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