Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

Detecting Soft Errors by a Purely Software Approach 43
According to these modifications‚ the studied rules become the following:
A boolean flag status_block is associated to every basic block i in the code;
“1” for the inactive state and “0” for the active state;
An integer value ki is associated with every basic block i in the code;
A global execution check flag (gef) variable is defined;
A statement assigning to gef the value of (ki & (status _block = status_block
+ 1) mod2) is introduced at the beginning of every basic block i; a test on
the value of gef is also introduced at the end of the basic block.
2.1.3. Errors affecting control instructions
These rules aim at detecting faults affecting the control instructions (branch
instructions). According to the branching type‚ the rules are classified as:
Rules addressing errors affecting the conditional control instructions (i.e.
test instructions‚ loops);
Rules addressing errors affecting the unconditional control instructions (i.e.
calls and returns from procedures).
2.1.3.1. Rules targeting errors affecting the conditional control instructions
The principle is to recheck the evaluation of the condition and the resulting
jump. If the value of the condition remains unchanged after re-evaluation‚
we assume that no error occurred. In the case of alteration of the condition
an error procedure is called‚ as illustrated by the example in Figure 4-3.
2.1.3.2. Rules targeting errors affecting the unconditional control instructions
The idea of these rules consists in the association of a control branch (called
ctrl_branch) flag to every procedure in the program. At the beginning of each
procedure a value is assigned to ctrl_branch. This flag is checked for consistency
before and after any call to the procedure in order to detected possible
errors affecting this type of instructions. The application of these rules is
illustrated in Figure 4-4.