Exclusive Monitor (AXI Exclusive Access Support) - Exclusive Monitor (AXI Exclusive Access Support) - 1.1 English - PG313

Versal Adaptive SoC Programmable Network on Chip and Integrated Memory Controller 1.1 LogiCORE IP Product Guide (PG313)
Document_ID
PG313
Release_Date
2026-06-23
Version
1.1 English

The NoC supports AXI exclusive accesses. The packetized transactions sent into the NoC carry the original 16-bit AXI ID that was presented to the NMU in the packet header.

For exclusive accesses to DDR memory, the NMU preserves the original size attributes of the transaction if the following is true:

  • The transaction length is 1
  • The size is 128 bits or less

The DDRMC can track up to eight exclusive accesses and the maximum AxSize of an exclusive transaction is 16 bytes. For all other transactions to DDR memory, the NMU treats the transaction as modifiable, packs the data together, and modifies the size to 128 bits.

The NSU contains a single AXI monitor. The monitor uses a 10-bit System Management ID (SMID) in the header as the ID for comparisons. An exclusive access is sent out as exclusive on the NSU AXI interface. The NSU suppresses an exclusive write access that fails the exclusive check in the monitor and it is not seen on the NSU AXI interface.

The end-to-end processing of an exclusive access proceeds as follows.

At the NMU:

  • The NMU receives the 16-bit AXI ID from the master.
  • The NMU receives the 10-bit SMID on the A*USER[9:0] inputs from the master.
  • For reads, the RROB indexed by the read tag stores the AXI ID.
  • The SMID, AXI ID, and the tag value are transmitted in the NoC packet header.

At the DDR memory controller NSU (MC):

  • The MC uses the SMID to check the exclusive monitor. You can also use the SMID for security and access permission checks.
  • For reads, the combination of read tag and NoC source ID is unique at the MC for each packet. The MC reorders based on this combination.
  • For writes, the tag is ignored and only the NoC source ID is used for reordering.

At a non-MC NSU:

  • The NSU uses the SMID for exclusive monitor check.
  • The NSU creates a master interface AXI ID by selecting two bits from the NoC source ID. This allows the NSU to reorder transactions from different masters, but does not reorder transactions from the same master.
  • The NSU stores the NPP tag and returns it with the response.