Digital data processing system including means for verifying data transferred from a non-volatile to a volatile store

Claim 1

A digital data processing system comprising a non-volatile data store (15) which is coupled through a system controller (11) to a volatile data store (12) and a data processor (14), the system being operable to save data during power-off periods by storing data from the volatile store in the non-volatile store and to transfer data from the non-volatile store to the volatile store during a power-on sequence following a power-off period characterised by verifying means for verifying data from the non-volatile store prior to transfer to the volatile store during a power-on sequence, said verifying means comprising a read-only store (22), first means (27) for providing a sequence of test addresses to the read-only store to derive therefrom, for each test address, a non-volatile store reference address, reference data related to test data at the reference address, and an address of a diagnostic routine in the read-only store related to a portion of the non-volatile store including the reference address, second means (25) for holding said reference data, third means (26) for holding said diagnostic address, fourth means (29) for holding data read from the reference address, and comparing means (21) for comparing the contents of said second and fourth means to provide, in accordance with the relationship of data therein, an output to control means (210) to cause the control means either to direct the next test address in the sequence, or said diagnostic address, to the read-only store.