Identifying Microcontroller from Retevis RT85 Handheld radio

[Cassus]

Hello,

I am trying to reverse engineer a RT85 Retevis handheld radio in order to produce a custom firmware. The main problem I have is to figure out the microcontroller they are using. They went through the effort of grinding the top of the chip to make it harder for people to guess what it is.
The remains of a logo is still distinguishable on the bottom of the chip. Does anyone recognize a brand logo? I doubt it is an obscure Chinese manufacturer otherwise they would have tried to mask it.

 

 

Also, the programming port has only 4 pins so I guess VDD, VSS, Data and Reset. That already excludes some brands like Microchip which uses at least 5 pins.

I have a J-Link, ST-Link, ICD3, Oscilloscope and Logic Analyzer if that can help.

here are the pictures:

 

 

 

 

The logo might just be from the manufacturer Beken, since they use other chips from that brand on the device but I can't find any matching MCU on their website

BTW, The TH-UV88 handheld radio from TYT uses the same PCB and doesn't erase the markings so if anyone has one lying around...