Exclusive Access

Zynq UltraScale+ Device Technical Reference Manual (UG1085)

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2.4 English

All exclusive read transactions have an EXOKAY response (except in the case of an ECC uncorrectable error). Successful exclusive write accesses have an EXOKAY response, unsuccessful exclusive write accesses return an OKAY response. If an exclusive write fails, the data mask for the exclusive write is forced Low and the data is not written. The DDRC monitors one address per transaction ID for exclusivity. Therefore, if a master does not complete the write portion of an exclusive operation, a subsequent exclusive read to the same ID changes the address that is being monitored for exclusivity. Once an exclusive access monitor for a given address is enabled, all write transactions are monitored for violation, regardless of the originating port. The violation check operates across the ports. The exclusive access monitor compares the exclusive write transaction address, size, length, ID, and port number against the exclusive read transaction address, size, length, ID, and port number, and only accepts an exclusive write when these parameters match. Otherwise, the exclusive write is considered as a fail. An exclusive access monitor is present in the DDRC. Zynq UltraScale+ devices support eight exclusive access address monitors for six ports.