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Date:      Tue, 10 May 2016 09:38:28 -0700
From:      bob prohaska <fbsd@www.zefox.net>
To:        freebsd-arm@freebsd.org
Subject:   Serial console trouble on RPI2
Message-ID:  <20160510163828.GA1049@www.zefox.net>

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In trying to set up serial consoles on a quartet of RPI2 hosts
two of the machine's consoles worked without explicit changes.
The other two don't seem to work. If anybody can give me a hint
what's wrong it would be much appreciated. 

The USB-serial adapters are these, using PL2303 chips:
Btek® WINDOWS 8 Supported Debug Cable for 
Raspberry Pi USB Programming USB to TTL Serial Cable

First, two RPI2s were set up with cross-connected consoles, so each 
provided serial access to the other. The setup worked without any issues.

Next, all four hosts were arranged in a ring, with each host providing serial
port access to the next in the ring. The two hosts which had working serial
consoles in the first place continue to present a serial console to the monitoring
host. The others do not, even after reboot. Here's an example:

On the monitoring host:
root@ns2:/home/bob # cu -l cuaU0 -s 115200

Connected
?

The monitored host was rebooted via the network. It came back up in good order,
but nothing appeared on the serial port. The kernel configs of all hosts are 
the same, dmesg on one "no console" machine reports in part:
FreeBSD 11.0-CURRENT #6 r292479: Sun Dec 20 07:09:08 PST 2015
.....
uart0: <PrimeCell UART (PL011)> mem 0x201000-0x201fff irq 65 on simplebus0
uart0: console (115200,n,8,1) 

In this particular case I can see the wires on the GPIO header and they're
in the right place. The USB-serial adapter is new out of the sealed box, 
so it seems unlikely to be defective.

The one difference among the hosts is FreeBSD revision number. The hosts
which offer usable serial consoles are r292412 and r299225, the two which
don't are r292479 and r297367. All four kernel config files contain:
# Comment following lines for boot console on serial port
device          vt
device          kbdmux
device          ukbd
which seems backwards but causes no trouble in two of the machines.

Any guidance appreciated!

Thanks for reading,

bob prohaska

 



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