After a kernel/busybox update my half-duplex /dev/ttyS1 port has become write only.
What works: echo "Hello ttyS1" > /dev/ttyS1
What doesn't work: cat /dev/ttyS1
Same pattern when I try writing c++ read/write interfaces: write works, read times out.
At this point I suspect a really low level misconfigured setting.
Does anyone know of any stty settings, system security flags, or similar that might be blocking receive on this one port or interfering with half-duplex 2-wire wiring?