External bus interface

I'm trying to implement something similar to the MMC interface with the Nios II through DMA and/or Avalon bus. This interface consists of 1 clock and 5 bi-directional data signals.

In the SOPC builder, I've added an interface to user logic with those signals defined, then tried using avalon register slave, avalon memory slave, and avalon master through the bus interface type pull-down selection. However, all gave me some sort of errors messages.

Please advise. Thanks.