Robust power-on meter and method using a limited-write memory

A power-on meter for a device, comprising:

• a data word having multiple bits in order of significance representing a count of events;
• a non-volatile memory for storing said data word and an associated error correction code (“ECC”), said non-volatile memory having a predetermined maximum permissible number of writes to each of its addressable locations;
• said data word being partitioned into at least a first subword having a group of less significant bits and a second subword having a remaining group of more significant bits, wherein said first and second subwords have permutations not exceeding the predetermined maximum permissible number of writes of said non-volatile memory and each subword is independently writable to and readable from said non-volatile memory;
• a count updating agent responsive to whenever said device is powered on for reading said data word from said non-volatile memory;
• said count updating agent incrementing said read data word by one count at predetermined events while said device is powered on;
• and
• whenever said read data word is incremented with a change in its first subword but not in its second subword, said count updating agent updating the first subword and the associated ECC in the non-volatile memory at their existing location;
• and
• whenever said data word is incremented with a change in both its first and second subwords, said count updating agent updating the second subword in the non-volatile memory at its existing location and also storing the changed first subword and the associated ECC in a location different from their existing ones in the non-volatile memory, the different location having an address dependent on the second subword.