[fedora-arm] Prevent Raspberry Pi U-Boot from listening to UART?

[Eric Smith]

I'm trying to use Fedora 28 Minimal on a Raspberry Pi 3 to set up an NTP
server using a GPS hat, specifically intended for this purpose:

https://www.tindie.com/products/nsayer/skytraq-venus838lpx-t-timing-gps-module-breakout/
(That link initially shows the non-Raspberry Pi version; click the second
photo for the Pi version.)

Booting Fedora from the MicroSD fails, apparently due to U-Boot thinking
that the UART has "pressed a key" to abort the boot. I get a U-Boot prompt,
followed by lots of garbage (presumably due to baud rate mismatch).

Is there any easy way to get U-Boot to not listen to the UART?

I've tried this with 32-bit and 64-bit Fedora 28 on a Pi 3B and a Pi 3B+,
with the same results. Without hte GPS hat it boots fine.

Thanks!

Best regards,
Eric

[Peter Robinson]

Post by Eric Smith
I'm trying to use Fedora 28 Minimal on a Raspberry Pi 3 to set up an NTP
https://www.tindie.com/products/nsayer/skytraq-venus838lpx-t-timing-gps-module-breakout/
(That link initially shows the non-Raspberry Pi version; click the second
photo for the Pi version.)
Booting Fedora from the MicroSD fails, apparently due to U-Boot thinking
that the UART has "pressed a key" to abort the boot. I get a U-Boot prompt,

From the prompt you should be able to types "boot" and it should
continue to boot.

Post by Eric Smith
followed by lots of garbage (presumably due to baud rate mismatch).

Or the GPS already sending NMEA data.

Post by Eric Smith
Is there any easy way to get U-Boot to not listen to the UART?

Off hand I'm not sure, there was a patch set that did auto enable
based on the what the firmware reported.

Post by Eric Smith
I've tried this with 32-bit and 64-bit Fedora 28 on a Pi 3B and a Pi 3B+,
with the same results. Without hte GPS hat it boots fine.

Yes, so it seems like the GPS is probably trying to send data which is
in turn interrupting the boot process.
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[Jeffrey Ollie]

Post by Peter Robinson

Post by Eric Smith
I'm trying to use Fedora 28 Minimal on a Raspberry Pi 3 to set up an NTP

Yes, so it seems like the GPS is probably trying to send data which is
in turn interrupting the boot process.

I had the same problem (except I was using the Adafruit version), and my
only solution at the time was to switch back to Raspbian. The GPS starts
sending data over the UART as soon as it is powered up so there's really no
chance for the user to do anything. Barring some sort of hardware/software
changes on the GPS HAT that would prevent it from sending data over the
UART until it got a signal from the Pi I think that U-Boot will need to be
changed so that it ignores the UART.

[Eric Smith]

Post by Jeffrey Ollie
I had the same problem (except I was using the Adafruit version), and my
only solution at the time was to switch back to Raspbian.

Yes, mine works fine with Raspbian also. I just don't much like using
Debian-based distributions because I have been using Red Hat and Fedora
since 1995.

[OT] It probably makes no difference in practice for a typical NTP server,
but the Geppetto board is based on a GPS chip with firmware optimized for a
fixed location time reference. After it does an initial site survey it
assumes that it doesn't move, and purportedly can offer better performance
on the PPS output.

[Eric Smith]

Post by Peter Robinson
From the prompt you should be able to types "boot" and it should
continue to boot.

There won't normally be a keyboard on the machine, and I need it to recover
from power failures.

Post by Peter Robinson

Post by Eric Smith
followed by lots of garbage (presumably due to baud rate mismatch).

Or the GPS already sending NMEA data.

It's sending NMEA data, but U-Boot sees it as garbage, presumably due to
baud rate mismatch.

Post by Peter Robinson
Is there any easy way to get U-Boot to not listen to the UART?
Off hand I'm not sure, there was a patch set that did auto enable
based on the what the firmware reported.

I was hoping that there was a configuration option that could be set
somewhere (maybe in a text file in the boot partition) to tell U-Boot not
to open the serial port at all.

[Peter Robinson]

Post by Eric Smith

Post by Peter Robinson
From the prompt you should be able to types "boot" and it should
continue to boot.

There won't normally be a keyboard on the machine, and I need it to recover
from power failures.

Sure, my point is that there's a means to make it continue.

Post by Eric Smith

Post by Peter Robinson

Post by Eric Smith
followed by lots of garbage (presumably due to baud rate mismatch).

Or the GPS already sending NMEA data.

It's sending NMEA data, but U-Boot sees it as garbage, presumably due to
baud rate mismatch.

The speed mismatch is irrelevant here, U-Boot is looking for some
input IE press any key and it'll interrupt boot, it could be valid
NMEA data at the right speed and it'll do the same.

Post by Eric Smith

Post by Peter Robinson

Post by Eric Smith
Is there any easy way to get U-Boot to not listen to the UART?

Off hand I'm not sure, there was a patch set that did auto enable
based on the what the firmware reported.

I was hoping that there was a configuration option that could be set
somewhere (maybe in a text file in the boot partition) to tell U-Boot not to
open the serial port at all.

Not that I'm aware of off hand, although it's not a feature I've been
asked about so I could have missed it. A quick grep through the
upstream U-Boot logs and I get [1], you might want to email the u-boot
list to see if it could be tweaked. I, with my Raspberry Pi on Fedora
maintainers hat on, don't have the time to chase this at the moment
but would be happy to assist where I can and of course will accept
patches. i work on the RPi in Fedora in my own time and it already
takes up a significant amount of the little spare time I have.

Peter

[1] http://git.denx.de/?p=u-boot.git;a=commit;h=55b8a2ddaae407c8e9b4afe5cf33f848f0c4f49f
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