On Tue, Oct 16, 2012 at 8:39 AM, Jeremy Bennett <[email protected]> wrote: > It's not truly FLOSS (restriction on commercial use), but Wattch source > code is available for non-commercial/non-profit use. > > http://www.eecs.harvard.edu/~dbrooks/wattch-form.html > > Another case of someone writing their own "open source" license, rather > than using a tried and tested one! > > This is probably the most widely used power estimation system for > mid/high-level analysis, certainly within the academic community. Its > proponents claim it is accurate to 10%.
Just my two cents: I've done lots of work with sim-wattch, and I don't trust its results. Modern architectures have deviated somewhat from what it simulates, and it simulates at a very abstract level. The way it maps the abstract out-of-order simulator back onto actual hardware components is what I don't trust. It's easy to cheat or make mistakes in your power estimation if you make changes to the simulator. Plus, it uses an 8-byte RISC-like instruction format, combined with all kinds of hackery to convert the results from using an 8-byte instruction to what you would get with a 4-byte instruction. On top of all that, it's a tremendous pain to work with, because it relies on a 10+ year old version of GCC that often generates incorrect code. You'll spend a lot of time just trying to figure out whether the bugs are in the compiler or in the simulator. Finally, it simulates an out-of-order core, which makes it unsuitable for simulating the power usage of the OR1200. You -can- tell the simulator to issue in-order, but it still simulates all the structures that an OoO core would have, so your power estimate won't be realistic. > Accurate power estimation by simulation is provided by commercial tools > operating at the gate level. It is critically tied into knowledge of the > target silicon process. These tools run extremely slowly (seconds per > cycle, rather than cycles per second for big chips), but apparently give > very good estimates. This is the way to go. It's slow, and lots of work, but I don't believe anyone would sincerely question the estimates you'd get this way, provided you simulate for a real process, and use an up-to-date simulator. Unfortunately, there is no way to do this with open source tools, and probably will never be. -Pete _______________________________________________ OpenRISC mailing list [email protected] http://lists.openrisc.net/listinfo/openrisc
