I have two USB-serial adapters with a null-modem serial cable between them, similar to this user. I can setup an IP connection easily between two linux (ubuntu) boxes running this command on one side:

pppd -detach crtscts lock /dev/ttyUSB0 38400 &

and this on the other:

pppd -detach crtscts lock /dev/ttyUSB0 38400 &

However, running the same command between a linux box and an embedded linux device (sama5d3x-mb) I receive the following error message:

Couldn't get channel number: Input/output error

This message can appear on either the desktop linux side or the embedded linux side, it just depends on which end the first command is issued. I also occasionally see this message:

LCP: timeout sending Config-Requests

Obviously something isn't setup correctly in the embedded environment. These are the only error messages that appear in the log.

If I instead open up the serial ports using putty/screen I can tx/rx characters back and forth just fine.

One thing I noticed is that on my desktop system I have a folder at /etc/ppp that contains many files. Such a folder does not exist on the embedded environment. I tried dumping a copy there with rsync. However, their presence doesn't seem to make a difference.

Both the deskop and embedded platform report pppd version 2.4.5

Google results mostly turn to dead ends. Short of browsing through the source code, or setting up a sniffer to inspect for any traffic on the lines, I'm sure not where to go from here. Any recommendations?

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