Each transaction source generates one or more 10-bit system management ID (SMID) numbers. The SMID is used by the SMMU, XMPU, XPPU, and IPI to identify the source of a transaction to ensure it has the authority to access the destination.
Every PMC and PS transaction is assigned one or more
unique SMID value starting with bit  = 1. One exception to this is the FPD CCI
snoop filter eviction controller, which uses an SMID value =
to move dirty cache data from the CMN caches to system memory.
Each non-PMC/PS transaction is assigned one or more unique number with bit  = 0. The SMID value is driven on the AxUSER channel.
When a transaction is routed through a TBU in the SMMU, the 10-bit SMID value is concatenated with a 5-bit stream field that is unique to each TBU in the SMMU.
The SMIDs are listed in Transaction Hosts.