/dev/ser1 and ksh - what causes ksh to exit?

I want to provide a shell via serial port on my custom target. I
believe tinit and /etc/config/ttys are configured properly. When my
target boots and I connect a null modem cable to the port serviced by
/dev/ser1, I’m prompted for a login. The login succeeds and I get a
shell - great.

However, sometimes when I disconnect and reconnect the null modem cable,
I’m greeted w/ a new login prompt (ksh exited) but other times I’m not -
the original shell is still active and a login is not required.

What prompts ksh to exit sometimes but not others? Is it looking for a
particular signal from devc-ser8250? Is this a hardware problem? I’m
looking for consistent behavior.

In my boot script I launch devc-ser8250 w/ the following args:

/proc/boot/devc-ser8250-jace5 -e -c25000000 -b57600 0xffffc000,1

My /etc/config/ttys file contains:

ser1 “/bin/login” qansi-m on

Thanks for any suggestions.

Dan Giorgis