SkajNätt

Connected an MCP23S17 SPI-GPIO chip, first outputs are successful.

Connected a serial VFD 4x20 character display to a UART. Does not use SkinnyBus8, so it is cheating a bit...
Wrote code that scans all 4 slots and prints info about the slots to the serial port (VFD). PnP enumerator :D

Exchanged the SRAM for EEPROM. Testing. Works as expected to read and write. Takes a bit of delay to complete writes.

Built another card, same as the other. Works with SRAM.

Some HW changes to get write protect of i2c working. Bus-board is 4 slots now.

All connections soldered. SW tests are OK, except for I2C write protect.
20MHz SPI works properly now!!! Actually running at 21MHz due to scaler and base-frequency. 5% overclock SHOULD be fine for most chips.

Built a proper expansion bus board, and an SPI-SRAM card. The RAM-card still has some connections missing.

Migrated to a larger board, everything tested to (still) work OK.

Connected another chip to the same I2C-bus. Using the 2 CS-lines it is possible to select which chip to use instead of addressing them separately. Another quick victory.
The board is getting crowded, time to move to something larger. And verify the i2c-speed, is it REALLY 400kHz?