In this paper we propose a C-b+ based cosimulation and cod&en environment. that allows to soecifv the timing behavior of the compo&ts of a complk h&dware-soft&m system independently of the functional refinement. While the hardware models are at a high functional abstraction level, thus resulting in a high simulation speed, yet the timing behavior can be specified with sufficient ~anultity to give relevant feedback concerning the timing of the software taski. We demonstrate this method on the design of the digital part of an ADSL modem.