pl2303 lockups on rpi2

[bob prohaska]

On Mon, Jun 20, 2016 at 10:59:55AM -0600, Ian Lepore wrote:
> 
> While I've heard more good things than bad about freebsd's support of
> pl2303, the one I can personally vouch for is FTDI.  We use them
> extensively at $work, which means basically I get paid to maintain the
> freebsd driver for them.
> 

Occasionally connection attempts produce a flood of question marks which 
does not seem to end (I've let it run several minutes). Makes me wonder
if there's some sort of wiring issue:

root at ns2:/home/bob # stty -f /dev/cuaU0
speed 9600 baud;
lflags: echoe echoke echoctl
oflags: tab0
cflags: cs8 -parenb clocal
root at ns2:/home/bob # stty -f /dev/cuaU0 sane
root at ns2:/home/bob # cu -l cuaU0 -s 115200
Connected
????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

In this case simply trying again brought up a login prompt. Trouble is, there has
been no sign of garbled characters, which I always took to be the signature of
something wrong on the serial side of things.

Each Pi in the quartet has its own isolated power supply, but all Pis share ground
through the network wiring. There's never been a hiccup on the network, however.

Next time one of the pl2303s locks up I'll repeat the serial disconnect to see if
that unsticks it without intervention on the USB side. If it does maybe this is a 
wiring or other hardware issue, not software.

Thanks for reading!

bob prohaska