Thank you very much for your questions.
1. HDL Coder does not perform any high-level synthesis in terms of scheduling, binding and allocation. Instead, HDL Coder performs a direct mapping between Simulink blocks and VHDL/Verilog constructs both for data-flow and control-flow dominated designs. The presented optimizations only address data-flow dominated designs.
2. For the same specification the word-length optimization will result in the same implementation as long as the same seed for the random number generator is used. Yet, you are addressing an interesting point, as small changes in the specification can result in completely different word-lengths in the implementation. The most important verification step here is the comparison between floating-point and fixed-point model. We achieve that by simulating both designs in Simulink using testbench stimuli that are representing the specified behavior of the design. After that, by considering the signal deviations, we examine if the fixed-point model still fulfills the spec. The verification between the Simulink model and the generated RTL code is also done simulation based.
3. For data-flow dominated designs, which are addressed by our optimizations, the resulting Simulink models and RTL implementations are verified as described above. Control-flow dominated implementations resulting from HDL Coder can be formally verified by property checking against properties that represent the specified behavior.
I hope I answered your questions. If any more questions occur, please feel free to post them.
A couple of questions coming from not very clear issues in the article:
1. How well does this methodology HLS perform to designs with complex control flow? I only show a couple of statements about data-path dominated (I suppose stream-based) designs...
2. It seems that because you are using simulated annealing to convert from floating point to fixed point, you will be getting different implementations from the same spec. every time you run the tool!
Isn't this a burden for verification groups?
3. I don't see any formal methods used in the translation flow, from simuling models down to HDL implementations. How do you guarantee the correctness of the functionality of results? Even more, how do you prove the implementation functionality matches that of the specification?