pppd on macos fail with "publish_entry SCDSet() failed"

Question

pppd is failing for me on the Mac. I'm trying to connect to a serial port to an embedded device running lwIP. It works from both Ubuntu and Yocto, BUT not from my Mac. Since I do my development on the mac, it would be nice to get it working on the Mac.

Here's how I'm calling it:

sudo pppd /dev/tty.usbmodem336D376733381 115200 172.168.0.1:172.168.0.2 noauth debug

I get the following message back:

Mon Aug 23 15:55:51 2021 : publish_entry SCDSet() failed: Success!

So it seems to have failed...but with Success, haha :)

Any suggestions what this could be?

Please note that I have verified that /dev/tty.usbmodem336D376733381 is the correct device and has ppp related data coming from it.

Thanks, Craig

Answer 1

Ok, I figured out what my issue was. I was using two FTDI serial converters connected like a null modem cable:

I did not have the flow control lines connected (because that would require soldering). In the man page for pppd, I saw that hardware flow control is ON by default. Since I didn't have those line connected, flow control was preventing data from flowing resulting in the error I was getting. I added the "nocrtscts" option to my pppd command and it now works. The command I ended up with is:

sudo pppd /dev/tty.usbmodem336D376733381 115200 172.168.0.1:172.168.0.2 noauth nocrtscts