Test technology development for processor-based Systems on a Chip (SoCs) has mainly focused on quality and cost of production test. More recently, test technologies that facilitate self test in the field of application are getting additional attention. Hardware-based built-in self test (BIST) is well understood for logic and for memory block, but can hardly cope with changing test strategies. We present a scalable test architecture based on a configurable test processor and a distributed modular scan controller that facilitates self test for logic and for bus structures and can optionally support externally controlled production test.