Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

Detecting Soft Errors by a Purely Software Approach 47
Table 4-1. Main characteristics of the studied programs.
CMA original
CMA hardened
Overhead
Execution time (cycles)
Code size (bytes)
Data size (bytes)
1‚231‚162
1‚104
1‚996
3‚004‚036
4‚000
4‚032
2.44
3.62
2.02
registers‚ the program code and the application workspace. During fault
injection sessions‚ faults were classified according to their effects on the
program behavior. The following categories were considered:
Effect-less: The injected fault does not affect the program behavior.
Software Detection: The implemented rules detect the injected fault.
Hardware Detection: The fault triggers some hardware mechanism (e.g.‚
illegal instruction exception).
Loss Sequence: The program under test triggers some time-out condition
(e.g.‚ endless loop).
Incorrect Answer: The fault was not detected in any way and the result is
different from the expected one.
In order to quantify the error detection capabilities‚ two metrics were introduced:
the detection efficiency and the failure rate
Where:
D represents the number of Software Detection faults
L is the number of Loss-Sequence faults
E is the number of Incorrect Answer faults
H is the number of Hardware Detection faults
3.1.1. Fault injection in the DSP32C registers
Table 4-2 reports the results obtained by injecting faults modeling a bit flip
in the internal registers of DSP32C processor. To obtain realistic results‚ the
number of injected faults was selected according to the total number of
processor cycles needed to execute the programs; indeed the faults injected
into the processor can affect the program results only during its execution.
Thus‚ 8000 faults were injected into the CMA Original‚ while 19520 were
injected for the CMA Hardened (according to the penalty time factor about 2
times given in Table 4-1).