1. A co-hosted cyclical redundancy check (CRC) calculations device, comprising a read snoop unit that is arranged to snooped data read from a mirrored memory that has data stored using a mirrored address; and a CRC co-generator that is arranged to receive the snooped data read from the mirrored memory and to use the snooped data read from the mirrored memory to calculate a CRC result when the snooped data read from the mirrored memory is read using an address that falls within a range of addresses of the mirrored memory over which the CRC result is calculated.