Progress March I - More schematics (Patreon)

Still working from time to time on the project. I recently did some schematic drawing and coarse component placement on the main board.

External memories, video and audio DAC, and basic I/O like debug UART, joypads, memory card, marquee and LED outputs, coin mech control, ... are done.

I still didn't have the courage to order the FPGA board, so I might instead order the main board first (with the same money from Patreon) and see how the board house quality turns out.

Also did some research on simulating the uPD4990 RTC chip, which can still be bought from NOS but will forcibly disappear some day. It seems that access is slow enough to use a general-purpose MCU with timekeeping functions.