Bug descriptions and solutions

This post is about bugs and their solutions on embedded Linux.

Bug 1
Remove internet connectivity on Gateway device. For the first time, plug in USB device with swupdate.swu, no firmware update is performed. For the second time, plug in USB device with swupdate.swu, firmware update occurs. When internet connectivity is removed, it should not do firmware update. So it is a bug.

Solution:
Check the gateway system time against x.509 certificate validity period. If system time is outside x.509 validity period, swupdate does not run. That is because swupdate software checks the x.509 certificate. The problem has nothing to do with internet connectivity.

# openssl x509 -in x509.crt -text -nount
validity: not before
              not after
# date
-- show system time

Compare the system time and x509 certificate validity

Bug 2
When using mobile App to connect to Gateway device via BLE, multiple occurrence of DBUS error message "Rejected send message" is seen in journal log. This error message should not happen.

Solution:
Using dbus-monitor, we can see the dbus system message. There is method call from Bluez to config daemon, there is a signal and method return in response to the method call. The method return is rejected by the dbus daemon and dbus error message is printed out.

The gateway sends GATT Indicate to mobile app, mobile app responds with GATT Confirm. The Indicate is used to transfer data. Confirm is the acknowledgement. When mobile app sends Confirm to gateway, Bluez receives it, it sends dbus confirm to config daemon. And the next chunk of data is sent from config daemon to Bluez. The method return is also sent out by the config daemon. The config daemon uses dbus python library.  The solution is in dbus python library. We have to check the dbus must_not_reply flag. If the flag is set, we stop the library from sending out method return.

Bug 3
If Gateway is physically connected to ethernet and has a wifi, and if ethernet link is not able to up, the gateway is not able to use wifi. The gateway should be able to auto failover to wifi.

Solution
Use network manager to check the link, if the ethernet link is not up, auto switch to wifi. The network manager config file provides checking of the link status.

Bug 4
When doing high throughput network application over ethernet , the CPU is loaded to over 90%.
This slows down the response time of other processes.

Solution:
The ethernet driver was using interrupt  driven mode, switching to NAPI , and implement TSO  so that segmentation of the packets is handled by NIC card.  This way reduces the CPU load.