Embedded software developers often write code that works with battery-backed devices or eco-friendly equipment. Usually they finish their code, measure its execution time and power consumption, and try to anticipate battery life with the acquired data. They have no preliminary knowledge of what the results might be, because they write code at high level of abstraction and can’t see the output assembly directly. Even if any assembly analysis is done, it can only estimate time performance, as long as data dependency is not involved.

Powot Simulator is an Instruction Set Simulator (ISS) that was first introduced in 2013 and did energy estimations on a C function-level basis. This approach, however, yields results that can be erroneous due to dependency of function’s code on input data. Version 2 of the simulator addresses this problem – by analyzing code on a statement-level basis one can achieve better energy estimates and localize the power-hungry sections of code. To do this, the simulator uses simple lookup table-based model files of microcontrollers.

The Powot Simulator v2 is a shared object library (libpowot_simulator.so) that could be part of a bigger development environment. It uses Lesser GPL v3 license which means that can be used free of charge by other open source and closed source programs.

1. The simulator depends heavily on the GCC toolchain. Install your cross GCC and provide its prefix in:

powot_simulator/simulator_configs/[arch name].cfg

where each tag contains the prefix and the command line parameters of the corresponding tools (nm, gdb, objdump):

SYMBOLLIST_COMMAND [compiler prefix]-nm GDBDUMP_COMMAND [compiler prefix]-gdb OBJDUMP_COMMAND [compiler prefix]-objdump -S -d

2. Next, provide a lookup table-based model of your target, that contains energy estimates for each instruction, in:

powot_simulator/models/mcu/[provider name]/[target name].mdl

If you can't make a model yourself check the existing ones.

3. Compile and link the code you want to analyze with NO optimizations, e.g.:

[compiler prefix]-gcc -O0 -o myfirmware.axf myfirmware.c

4. The repository powot_simulator_v2 contains an example front-end application, called "powsimu", that uses the shared object file "libpowot_simulator.so", and is a good starting point for your first simulation. Change to the directory where the executable "powsimu" is (powot_simulator_v2/powot_simulator_build/powsimu) and type:

powsimu -j /path/to/your/executable/myfirmware.axf -a [arch name] -p [provider name] -m [target name] -e [function name]

where [function name] is the name of the function from the executable file myfirmware.axf that needs to be analyzed (simulated).

Note: to make the executable work you must have Qt-Creator installed on your machine. Also make sure that you export the .so library of the simulator in your LD_LIBRARY_PATH (on Ubuntu):

export LD_LIBRARY_PATH+=:/path/to/git/project/powot_simulator_v2/powot_simulator_build/powot_simulator

If you run:

echo $LD_LIBRARY_PATH

you should see the correct path to the build directory of the simulator.

5. The simulation may take anything from milliseconds to seconds depending on the call tree and the size of the analyzed function. When it finishes an energy table will be printed.