The local snoop filter look-up table is sized for the 1 MB APU L2 cache and a 256 KB PL cache. Larger PL caches are supported. When the snoop filter look-up table does not have room for a cache-tracking entry, the snoop filter controller evicts a table entry out to system memory and sets up a new entry for the cache look-up.
Snoop Filter Memory Access Reads
When the snoop filter controller needs to update the look-up table, it reads from memory using the SMID attribute from the host that is requesting the memory coherent transaction. The SMIDs for each host are listed in a table in the System Management ID section.
Snoop Filter Memory Access Writes
If the snoop table entry is already occupied, the CCI must evict the entry and write it out to system memory. In this case, the CCI always uses an SMID attribute value of 00_0000_0000.
The XMPUs that protect system memory need to be programmed to allow these write transactions from the snoop filter in the CCI.