[MinnowBoard] PCIe warm boot behaviour

[Berth-Olof Bergman]

Hi,

This is because the Silverjaw lure uses the PMC_CORE_PWROK as PCI reset. They should use the PMC_PLTRST# instead. The PMC_CORE_PWROK is an input signal for telling the PMC that the power is good and stable. After the PMC_CORE_PWROK is high, the PMC will wait for PMC_SUS_STAT# to be stable before it raises the PMC_PLTRST#.

The problem is that when you do reboot the PMC_CORE_PWROK will already be active, so the reset signal (PMC_CORE_PWROK) will not go low and your PCI device is not reset. If you power down and the on again, the mandatory PCI reset of 100 millisecond is violated. This reset should be done when power is stable and would be if the Silverjaw lure had connected the PMC_PLTRST# signal to the PCIe slot reset.

There are no software solution to this problem. The only thing you can do is to start the board cold and not from standby (S5). When you do, your board will have power really early enough so the PMC_CORE_PWROK cycle is long enough to reset your PCIe device.

See the include drawings for clarifications.

Best regards,

B-O Bergman Winzent Technologies


 
> 13 aug 2015 kl. 20:34 skrev Jackson Wiegman <jdwiegman at gmail.com>:
> 
> I am just getting started with a Minnowmax and Silverjaw lure, running an Ubuntu distribution.
> 
> I have a mSATA and a mPCIe device connected via the Silverjaw lure. On initial power and power-up, the mPCIe device comes up fine. However, when I do a reboot or power-down (with power still physically connected), the device fails to come up.
> 
> I don't have a lot of experience with coreboot or PCIe subsystems, so I wanted to reach out to the community to see if anyone has experienced this or can point me in the right direction.
> 
> Thanks!
> 
> Jackson
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> elinux-MinnowBoard at lists.elinux.org
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