SPRUJ28E November 2021 – September 2024 AM68 , AM68A , TDA4AL-Q1 , TDA4VE-Q1 , TDA4VL-Q1
Circular addressing modifies how the DRU performs address arithmetic so that addresses remain within a power-of-two sized window. Circular addressing works by holding upper address bits constant during an address update, while allowing the lower address bits to vary. This contrasts with the default linear addressing which allows all of the address bits to vary.
The TR provides address mode selection for each level of loop nest. Each level can select between linear addressing or circular addressing with one of two circular block sizes.
If circular addressing mode is selected in the AMODE field of the TR, the definition of the upper 16 bits of the FMTFLAGS field of the TR select the type of addressing for each entry in the loop and define two unique masks that can be used for the circular buffering. Additionally, the DIR field in the TR determines if the circular addressing flags apply for the source or the destination of the block move. The other direction always follows the standard linear addressing that is used if AMODE is not set.
For more information about circular buffering and the associated TR fields, see Circular Address Mode Specific Flags of DMA Architecture.