# Proposal of an Adaptive Fault Tolerance Mechanism to Tolerate Intermittent Faults in RAM
## 4 Assessment of the Adaptive Fault Tolerance Mechanism
### Outcomes
In this figure, besides \(\mathrm{P_{F}}\) and \(\mathrm{P_{L}}\), in the \(Y\)-axis, we have also calculated the detection and recovery coverages (\(\mathrm{C_{D}}\) and \(\mathrm{C_{R}}\)), as well as the percentage of intermittent errors detected (\(\mathrm{P_{I}}\)). These parameters do not make sense in the Plasma core, and for this reason, they did not appear in Figure 7.  
From the figure, we can observe that all single (transient or intermittent) faults provoke 0% of both failures and latent errors. Regarding coverages, 100% of single transient faults are corrected, whereas, in the case of intermittent faults, these coverages depend on the fault model, the fault timing, and the burst length. Similar to Plasma core, the recovery coverages get to 100% only in intermittent faults with burst length in the range [10; 20] (and particularly IBF faults and ISA faults with \(\mathrm{t_{A}}\) and \(\mathrm{t_{I}}\) in the range [10T, 100T]). Regarding the percentage of intermittent faults detected, they take values near to 100% only in ISA faults with \(\mathrm{L_{Burst}}\) in the range [10; 20] and \(\mathrm{t_{A}}\) in the range [10T, 100T] (in the figure, only the experiment with \(\mathrm{t_{I}}\) in the range [10T, 100T] is shown). The reason for this behavior lies in the nature of intermittent faults described earlier: not all intermittent errors can be detected because some fault activations are masked, either because the memory address affected is not accessed while erroneous (if caused by an ISA fault) or because they cancel in pairs (if caused by an IBF fault). Concerning multiple transient faults, we can observe that the recovery coverage is 0% in all cases, while 100% of failures plus latent errors are detected in case of double faults. This is an expected result, as the Plasma_ADAPTIVE core starts operating with the SEC-DED code, which only can detect double faults. In this figure, we can also observe a natural masking effect in multiple transient faults, but in this case, it is between 15% and 30%. Figure 8: Influence of faults in Plasma_ADAPTIVE core. Transient and intermittent faults. Figure 9 depicts the behavior of Plasma_ADAPTIVE core in the presence of combined faults. In this case, we have combined an ISA fault model, with L\({}_{\text{burst}}\) in the range [10, 20], t\({}_{\text{A}}\) in the range [10T, 100T], and t\({}_{\text{I}}\) in the range [10T, 100T] with the following transient (BF) faults occurred after the ECC swap:  
* Single faults (labeled in the \(X\)-axis as _1 xTr_\(\times\));
* Double random faults (_2 xRTr_);
* Double pseudorandom faults (_2 xPSRTr_);
* Double adjacent faults (_2 xATr_);
* Double pseudo-adjacent faults (_2 xPsATr_);
* Triple random faults (_3 xRTr_);
* Triple adjacent faults (_3 xATr_);
* Triple pseudo-adjacent faults (_3 xPsATr_). As explained in Section 4.2, the \"pseudo-\" experiments mean that the bit detected as EPB is mandatorily affected in the transient injection performed after the system swap. Like in Figure 8, five columns are presented per experiment: the percentage of failures (P\({}_{\text{F}}\)), the percentage of latent errors (P\({}_{\text{L}}\)), the detection and recovery coverages (C\({}_{\text{D}}\) and C\({}_{\text{R}}\)), and the percentage of intermittent errors detected (P\({}_{\text{I}}\)). Note that the percentage of intermittent errors detected is about 95% in all cases. This is because it only depends on the initial intermittent fault injection (corresponding to _ISA [10-20, 10T-100T, 10T-100T]_ experiment in Figure 7), and thus the behavior is always the same. The rest of the measurements depend on both the intermittent fault and the subsequent transient fault. We can observe that in all cases covered by the EPB3932 code (that is, single -1\(\times\) Tr label-, double random including the EPB -2\(\times\) PsRTr-, double adjacent including the EPB -2\(\times\) PsATr-, and triple adjacent including the EPB -3\(\times\) PsATr-), both correction and detection coverages are 100%. In addition, 100% of double adjacent faults are detected.