Hi all,
I was tinkering with the mainboard a little bit and here is the complete block diagram I drawn, according to the components (I omitted the connectors, since they have markings on the silkscreen):
There is NO uC in this board. All controlling is done by the Allwinner R528-S3 CPU.
https://bbs.aw-ol.com/assets/uploads/files/1645007527374-r528_user_manual_v1.3.pdf
The Onboard flash is a 8 GB KLM8G1GETF-B041
https://semiconductor.samsung.com/estorage/emmc/emmc-5-1/klm8g1getf-b041/