Serial console trouble on RPI2

[bob prohaska]

It looks like the problem is with USB: After rebooting the
Pi on the USB end cu runs but no connection results:

root at www:/home/bob # cu -l cuaU0 -s 115200

[carriage returns echo, but no login prompt]
[next, unplug and re-plug the usb connector]
cu: unsupported speed 115200
root at www:/home/bob # 
[try cu again]
root at www:/home/bob # cu -l cuaU0 -s 115200
Connected


FreeBSD/arm (www.zefox.net) (ttyu0)

login: 
[now all works as expected]

Any ideas how to fix this? The message about unsupported speed suggests
a configuration error, but in single user I don't think /etc/ttys or
/etc/gettytab comes into play. 

Thanks for reading and any suggestions,

bob prohaska

On Tue, May 10, 2016 at 09:38:28AM -0700, bob prohaska wrote:
> 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 at 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
> 
>