change my parameters and view them during simulation
While I can not speak for Simulink, I can tell you that our product, VisSim/ECD, performs model based development in much the same way and supports the JTAG link directly allowing the interactive gain change and system response observation that you desire. Since VisSim connects directly to the JTAG driver, our linkage is much faster and supports the new F28027 XDS100 $39 controlSTICK from TI. VisSim also supports on-chip triggered signal buffering for digital scope display on the PC of any wave form on the target. Target sample rates of up to 1 MHz are possible.
You can download a 2 month trial of VisSim/ECD here: http://www.vissim.com/downloads/demos.html
You can import your Simulink diagrams from the VisSim > Tools > Import menu option.
You can view a webinar showing how our interface works here: http://www.vissim.com/Movies/movies.html