Workaround for Stuck Beacon Problem

Stuck beacon is a notorious problem on madwifi (the wireless driver DD-WRT used for Atheros routers).  If you never experienced any wireless interruptions with DD-WRT then just ignore this article. However, if you're annoyed by this stuck beacon problem with constantly dropping wireless connection, then I hope this can be of help.

I personally prefer the open source ath9k driver which doesn't suffer from this, but some important feature like WDS is missing from ath9k. So to each its own, DD-WRT has the perfect reason to stick with madwifi and I don't expect the switch to ath9k anytime soon. And, seems that the problem only happens under certain circumstance. In my case, the connection drops with an Atheros wireless N card -- same card works great with stock firmware -- but works fine with another Intel WiFI 1000 11N card. So if a stable wireless connection is very important, the best solution might be flashing back to stock firmware or just try another card.

Below is a quick hack, not a completely fix but would make life a little easier. The idea is to watch the output of dmesg and when the "stuck beacon" error messages flood, reset the wireless interface to bring it back to life.

1. The watchdog script
   When wireless connection is dropeed, a typical out from dmesg would like this
   
   ath_bstuck_tasklet : Entering
   Resetting; Code: 01
   ath_bstuck_tasklet : Entering
   Resetting; Code: 01
   ath_bstuck_tasklet : Entering
   Resetting; Code: 01
   ath_bstuck_tasklet : Entering
   Resetting; Code: 01
   ath_bstuck_tasklet : Entering
   Resetting; Code: 01
   ath_bstuck_tasklet : Entering
   Resetting; Code: 01
   
   the same error message will keep repeating and flood the kernel log. So we can use this as a trigger and reset wireless interface when the error occurs.
   
   Below is the /opt/usr/local/bin/wifi-watchdog.sh script
   
   #!/bin/sh

   dmesg | tail -n 5 | grep -q ath_bstuck_tasklet || exit

   echo fixing...
   #a log file
   echo `date` >> /tmp/wifi-wathdog.log
   
   ifconfig ath0 down
   #for VAP, bring additional interface(s) down
   #ifconfig ath0.1 down
   sleep 2
   ifconfig ath0 up
   #bring it back
   #ifconfig ath0.1 up
   
   Set permissions
   chmod a+x /opt/usr/local/bin/wifi-watchdog.sh
   

2. Set cron job
   With the watchdog script ready, we can use cron to set it run every one minute.
   Add a new job:

   * * * * * /opt/usr/local/bin/wifi-watchdog.sh
   
   

   and it's done. Again, its not a completely fix just save the trouble of resetting the router each time.