[MinnowBoard] System power/reset control architecture with PCIe
leighgawne at gmail.com
Tue Mar 10 21:00:38 UTC 2015
Thanks very much for the information, very helpful. PCIe TX diff pair caps
and I2C level shifters already in place :-)
Out of interest, is there a published schematic for the Mini PCIe Lure
Re-reviewing after your comment I will definitely go with the PWROK signal
with an assembly option for an alternative RC as you have suggested.
Will post some more information on the design as things progress.
All the best,
[mailto:elinux-minnowboard-bounces at lists.elinux.org] On Behalf Of Anders,
Sent: 10 March 2015 20:20
To: MinnowBoard Development and Community Discussion
Subject: Re: [MinnowBoard] System power/reset control architecture with PCIe
1) Yes this is an acceptable approach. It's not the cleanest solution,
but it should work as long as your power up sequence is followed.
2) Just remember the i2c interface on the HSE is at 1.8V , so if you
are connecting it up to the mPCIe connector you will need to level shift it
to 3.3V. make sure you include the appropriate caps in series for the
PCIE_TX pair coming from the HSE.
3) The two implementations we have tested use the PWROK or a basic RC
for the PERST# signal on the mPCIe connector. In fact all of the designs we
have tested have zero ohm resistor options so either may be used. I would
not recommend using the #PMC_PLTRST_R_V1P8 signal.
Feel free to post schematics for review! Good luck with the design!
[mailto:elinux-minnowboard-bounces at lists.elinux.org] On Behalf Of Leigh
Sent: Monday, March 9, 2015 5:10 AM
To: elinux-minnowboard at lists.elinux.org
Subject: [MinnowBoard] System power/reset control architecture with PCIe
I am in the process of designing a custom expansion board for the
MinnowboardMax (really liking my experience with this board so far BTW :-)
and have a question regarding PCIe power supplies.
One of the interfaces I am implementing on the expansion board is a Mini
PCIe card slot. On my expansion board, I have all the required power
suppliers for card slot, and hence don't need to rely on any power coming
from the MinnowboardMax expansion connector.
There is a requirement in the Atom e38xx documentation (actually a PCI
Express 2.0 spec requirement) that all power rails associated with PCIe
should be valid for ~100ms prior to PMC_CORE_PWROK assertion.
>From what I can see in the MinnowboardMax schematic, there is an RC which
controls the assertion of SYS_PWRGD providing 100ms delay as part of the
power sequencing. My understanding is that as long as I ensure that my PCIe
supplies are up before providing 5V to the MinnowboardMax, then I should be
meeting this requirement. So a couple of questions just for clarification:
1) Is this an acceptable approach to take given the MinnowboardMax
power supply architecture? I have a seen there is a Lure expansion board
that includes mini PCIe and I presume this derives the required supplies
from those provided on the expansion header (perhaps the +5VSB supply, which
should also mean this constraint is met).
2) Any other recommended design approach? Backfeeding is always one
area of concern I have which I need to manage carefully - just want to make
sure there is nothing else I am overlooking/am not aware of.
3) I am intending on using #PMC_PLTRST_R_V1P8 as the system reset
signal for PCIe card slot and some other devices (with appropriate buffers)
- any thoughts here?
Many thanks for any information/clarification!
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