The memristor crossbar has the characteristic of high parallelism in implementing the matrix vector multiplication which can speed up the computation of the neural network. However, faulty me-mristors resulted from the hardware defects significantly degrade the classification accuracy of neural networks deployed onto the crossbar. Weight mapping is a type of low cost fault tolerant scheme. Unfor-tunately, the existing schemes usually conduct fault aware weight mapping in the entire row granularity which constrains the optimization space for fault tolerance. To overcome above mentioned problem, in this paper, we propose the operational unit (OU) level weight mapping which further adjusts mapping of the weight blocks inside each OU after the row granularity weight mapping. Such strategy can implement fine-grained fault tolerance. Moreover, we unify the similar inputs for the different OUs in order to con-strain the increase in the number of input vectors resulted from the OU level mapping adjustment. The experimental results demonstrate that with the defect ratesof 5%, 10%, 15% and 20%, on average classi-fication accuracies of the networks optimized by the proposed scheme are improved by 1.165%, 4.38%, 10.73% and 12.58% compared tothe ones of the row level weight mapping. Moreover, on average num-bers of the input vectors are reduced by 61.8%, 73.2%, 75.3% and 64.9%, compared with the OU level weight mapping without considering unification of the similar inputs.

Fault tolerance; Memristor crossbar; Neural network; Weight mapping; Reliability