SPRUJ28E November 2021 – September 2024 AM68 , AM68A , TDA4AL-Q1 , TDA4VE-Q1 , TDA4VL-Q1
The first N virtIDs can be reserved for DMA class usage in the PVU_VIRTID_MAP1 register. These virtIDs map to TLBs along with classes that are defined in the chanID bits 10 to 11 on the bus. This creates four classes per virtID, that can select from four TLBs, allowing the transaction to restrict its translations to smaller sets from known distinct memory segments (such as the DMA accessing descriptors or buffers). A set of bitfields define the class mapping, which defines the final class value to use for an input class, and can be used to restrict the number of classes if all four are not used (by mapping 2 to 0 and 3 to 1 for example to limit to two classes). Then the final TLB selection is calculated as:
The unused classes cause unused TLBs as entry points, but they can be used in chaining.