I have resolved the issue now: I have commented out the following in my init.rc file #service console /system/bin/sh # class core # console # disabled # user shell # group shell log readproc # seclabel u:r:shell:s0 # setenv HOSTNAME console # shutdown critical The console service was configured to use the same UART serial port that I was using for the PPP connection. It would interfere with pppd by resetting or controlling the serial port, causing the "Modem hangup" issue. I have a stable connection now running for the past 60 minutes. There is a ppp connection established between Ubuntu Machine and my AOSP Target Device. I can ping from AOSP target device into the Ubuntu Machine the following (it works): ping -I ppp0 10.0.0.1 (I have to use -I and provide the specific interface to ping even though the ip route is up to date) And I cannot ping from Ubuntu to AOSP target. Strangely, tcpdump shows that packets are received/sent back and forth # tcpdump -i ppp0 tcpdump: verbose output suppressed, use -v[v]... for full protocol decode listening on ppp0, link-type LINUX_SLL (Linux cooked v1), snapshot length 262144 bytes 14:49:17.949046 IP 10.0.0.1 > 10.0.0.2: ICMP echo request, id 552, seq 618, length 64 14:49:18.320546 IP 10.0.0.2 > 10.0.0.1: ICMP echo request, id 15, seq 34, length 64 14:49:18.351262 IP 10.0.0.1 > 10.0.0.2: ICMP echo reply, id 15, seq 34, length 64 14:49:18.972947 IP 10.0.0.1 > 10.0.0.2: ICMP echo request, id 552, seq 619, length 64 14:49:19.321893 IP 10.0.0.2 > 10.0.0.1: ICMP echo request, id 15, seq 35, length 64 14:49:19.353363 IP 10.0.0.1 > 10.0.0.2: ICMP echo reply, id 15, seq 35, length 64 14:49:19.997088 IP 10.0.0.1 > 10.0.0.2: ICMP echo request, id 552, seq 620, length 64 14:49:20.323381 IP 10.0.0.2 > 10.0.0.1: ICMP echo request, id 15, seq 36, length 64 14:49:20.356685 IP 10.0.0.1 > 10.0.0.2: ICMP echo reply, id 15, seq 36, length 64 I am not blocked any more, but it would be good to know if there is a way for: 1. I would be able to ping from Ubuntu machine as well into the AOSP target 2. Ideally, ping should work without -I and having to explicitly mention the interface (something like just ping 10.0.0.1 should work instead of ping -I ppp0 10.0.0.1 Thank you. On Tue, Sep 10, 2024 at 4:53 PM Paul Mackerras <paulus@xxxxxxxxxx> wrote: > > On Tue, Sep 10, 2024 at 11:30:48AM -0700, Devesh Chipade wrote: > > In my options file, I have debug and kdebug 7. > > This is all the logs I could get: > > The pppd logs look fine. There is nothing in the kernel (dmesg) log > that looks relevant (in fact kdebug 7 is mostly useful if you are > actually debugging the kernel driver; it doesn't really help with > problems like this). > > Do you have logs from pppd on the ubuntu/linux side? Is something > causing it to terminate? > > Alternatively, do you have another service running on either side > which also thinks it is using the same serial port? Something like a > getty, or whatever the systemd equivalent is for providing a login > prompt? You could do "fuser /dev/ttyMSM0" or "fuser /dev/ttyUSB0" as > root during the 6 seconds when the link is up to check if something > other than pppd also has the serial port open. > > Paul.
