The simulation semantics for M-Hwcosim differs from that used during hardware co-simulation in a System Generator block diagram; the M-Hwcosim simulation semantics is more flexible and is capable of emulating the simulation semantics used in the block-based hardware co-simulation.
In the block-based hardware co-simulation, a rigid simulation semantic is imposed; before advancing a clock cycle, all the input ports of the hardware co-simulation are written to. Next all the output ports are read and the clock is advanced. In M-Hwcosim the scheduling of when ports are read or written to, is left to the user. For instance it would be possible to create a program that would only write data to certain ports on every other cycle, or to only read the outputs after a certain number of clock cycles. This flexibility allows users to optimize the transfer of data for better performance.