The on-chip memory (OCM) contains 256 KB of memory that is accessible with its 128-bit AXI interface port. The OCM also includes ECC data protection.
The 256-bit memory array provides high bandwidth for AXI read and write transactions. Optimal bandwidth is achieved when the read and write accesses are a multiple of 256 bits with 256-bit address alignment. The OCM controller implements a read-modify-write function to accommodate writes that are not 256 bits in size or are not aligned to a 64-bit boundary.
The OCM controller arbitrates between the read and write channels. The OCM has eight exclusive access monitors that can simultaneously keep track of up to eight exclusive access transactions.
Accesses to the OCM are protected by the OCM_XMPU protection unit. It divides the OCM memory space into 64 memory blocks of 4 KB each. Each block is assigned security attributes independently.
The OCM is accessible via the LPD OCM switch, which includes the two Cortex-R5F processors, and others with access to the LPD or FPD main switches. Memory accesses from the RPU are treated with a higher priority than memory transaction requests from others.
Coherency
The OCM is normally accessed by the RPU, however, it can also be accessed by the APU. In cases where both the APU and the RPU use the OCM, and the APU caches the OCM memory range, the RPU can snoop the APU cache to maintain I/O coherency by routing the transaction through the FPD coherent interconnect. The APU cannot snoop the RPU caches if the RPU caches the OCM memory range.