It it’s current incarnation, the Steckschwein consists of 4 main units:
- IO (VIA 65c22), now also including UART
- Video / audio board with V9958 VDP and YM3812 (OPL2) sound chip
The 62c22 VIA is mainly utilized as SPI master to implement SPI as the main peripheral bus, connecting SD-card, RTC and the ATmega8 (used as PS/2 controller) to the system. The block diagram shows how things are working together.