I own a Wiko Fever 4G, and Android phone employing the Mediatek MT6753 SoC, which shipped with Android 6.0. Recently, I decided to pimp it by installing madOS, a custom ROM based on AOSP 8.1 supporting specifically that SoC.

The project dates back to 2018 and seems now dormant, but this ROM is very good and useful to people like me who don’t want to throw away a working phone because the stock system is outdated.

The only problem I had with this ROM, which was also mentioned by a user in the linked thread and never fixed, is that the LED does not blink when notifications are displayed. It only lights up when the battery is charging.

I did my own investigations and found that there is a bug which breaks LED blinking. That is, you can set any LED to be on or off, but the moment you ask it to blink it will simply go off.

LED’s are controlled by a set of files found under /sys/class/leds/$COLOR/, where $COLOR can be green, red or any other color your phone supports. My model only has green and red.

Each LED has files like brightness, delay_on, delay_off and trigger which control the LED brightness, if it should blink or persist an which events should cause it to blink.

Now, to have a LED blink, you should set delay_off to the number of milliseconds the LED should stay off, and delay_on to the number of milliseconds the LED should stay on. Setting both to 500 would cause half-second blinking.

What actually happens is that, every time one of the delay_* files is written, the other one is reset to 0. This will cause the LED not to blink, and it will either stay on or off depending on which file is written last. In my case, the library code controlling the LED’s writes delay_off last, which causes the delay be set to “on for 0ms, then off for XXXms”. This clearly means the LED does not have an on period, so it stays off.

Luckily, the system allows disabling blinking for notifications. One can go under Settings -> Apps & Notifications -> Notifications -> Notification light then, under the General heading, uncheck Blink light.

From this moment on, notifications will trigger a persistent LED. Be sure to choose the green LED for this, as red is already used for the battery, so that if a notification arrives when the phone is charging, you can still spot it.