Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

46 Chapter 4
of interest (where the results are stored) in a file res.dat. Then it closes
d3sim.
Finally‚ command (3) is needed to run the studied application in the simulator.
Since particular bit flips may perturb the execution flow provoking critical
dysfunction grouped under the “sequence loss” category (infinite loops or execution
of invalid instructions for instance) it is mandatory to include in the
“.ex” file a command implementing a watch-dog to detect such faults. A
watchdog is implemented by command (0) which indicates that the program
has lost the correct sequencing flow. TOTAL_CYCLES is referring to the total
number of application states machine.
In order to automate the fault injection process‚ a software test bench
(Figure 4-7) was developed.
First step of this test bench activates twice a random number generator [12]
to get the two needed bit-flip parameters: the occurrence instant and the target
bit‚ the latter chosen among all possible targets (memory locations and registers).
With these parameters‚ a command file is written and d3sim simulator
is started. The d3sim will simulate the execution of the studied
application by the DSP32C according to the commands of the generic file.
The last step will check results and compare them with the expected pattern
this to classify the injected faults.
3.1. Main characteristics of the studied programs
The application that we considered for the experimentation was a Constant
Modulus Algorithm (CMA)‚ used in space communications. This application
will be called in the following CMA Original. The set of rules above described
were automatically applied on the CMA Original program‚ getting a new
programs called in the following CMA Hardened. Main features of these
programs are summarized in Table 4-1.
The experiment consisted in several fault injection sessions. For each
program were performed single bit flip injections targeting the DSP32C