Like any beginner, I decided to replicate an existing project titled Handheld Game Console by Thanh Nhan Tran. Two changes -- (i) instead of using an LCD, I used the 7-pin SSD1306 OLED; (ii) does not include the speaker. I admit that the hardware prototype is not even close to the original but it was fun prototyping on breadboard.
Since this is a replica and not a tutorial, I did not include any block diagrams and flow charts explaining the logical structure and functionality of the system. In other words, the hardware block diagram, the software architecture and the data flow diagram is same as the original (except for replacement of LCD with OLED and omission of speaker along with its timer interrupt).
When faced with the same problem of slow OLED refresh rate, the SPI write speed (clock) was increased by experimenting and arriving at an appropriate the prescalar value.
The images are shown below.
All I want to say is that I had fun recreating this with limited functionalities.
This is the link to the github repo.