Exclusive Access - Exclusive Access - 1.0 English - PG247

When the exclusive-access feature is enabled (see Advanced Properties), the arlock and awlock signals presented by a connected master propagate to the MI.

An endpoint slave typically implements an Exclusive monitor that tracks Exclusive read requests for each of the endpoint masters that can access it, according to the AXI protocol rules. When using SmartConnect, AXI ID signals cannot be used to identify the original master of a transaction. Instead, AMD recommends using the aruser and awuser signals to convey master identification information. Some processor hard blocks in AMD devices monitor Exclusive transactions using the same "SMID" value used by their internal MMU for address mapping and access control. Some processor blocks can sample SMID directly from the aruser and awuser signals on their AXI interface. The AXI Sideband Formatter Utility IP can be used to inject a constant SMID value onto the AxUSER signals on behalf of a connected master. For slaves that rely on the AXI ID signals for Exclusive monitoring, the Sideband Formatter IP can also recover SMID values from the USER signal and present them on the corresponding AXI ID signals going to the slave.

Before propagating transactions to an endpoint MI, read and write transactions are subject to various transformations performed by SmartConnect:

Splitting

When transaction splitting is performed, typically due to downsizing or protocol conversion, the AxLOCK signal is always forced to zero. Exclusive operations cannot survive splitting.

Data-width conversion

The AxLEN value is modified to conform to the downstream data width, according to the original AxLEN, AxSIZE, and the alignment of AxADDR. This transformation is symmetrical between read and write commands. The LOCK signal is propagated.

Burst packing

When the original transaction indicates a narrow burst or the transaction is upsized, the resulting transaction observed at the endpoint MI is always fully packed. This transformation is symmetrical between read and write commands. The LOCK signal is propagated.

WRAP burst conversion

When the original transaction indicates a WRAP burst (if supported), SmartConnect always converts it into one INCR burst starting at the wrap address. This transformation is symmetrical between read and write commands. The LOCK signal is propagated.

AXI protocol requires that any master issuing Exclusive transactions must use identical transaction characteristics (ADDR, LEN, SIZE, BURST) between corresponding read and write commands. When SmartConnect transformations are symmetrical between read and write, this requirement is met on the SmartConnect endpoint MI. Even though the transaction characteristics of the original transaction are transformed, the read and write command characteristics issued on the endpoint MI match each other, provided the originally received commands conform to protocol.