SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The DSP C66x CorePac located extended memory controller (DSP_XMC_CTRL) implements a local DMA master port (MDMA) which provides the primary path for C66x CPU and cache requests to the device level memories such as (DDR or L3 SRAM) and peripheral / memory mapped register space. Via some additional logic, including DSP_SYSTEM controls and a local DSP MMU - DSP_MMU0 on the path (with option to bypass), C66x local MDMA port is mapped to the DSP subsystem CPU master port (i.e. MDMA master port of the DSP CPU on L3_MAIN). The DSP C66x Corepac MDMA port is mapped to the DSP Subsystem CPU Master Port (with DSP_MMU0 involved or not involved) to allow fast accesses (DSP_NoC not involved) to the external SDRAM (via the L3_MAIN and DMM) or to L3 SRAM (via the L3_MAIN).
The memory protection settings in MPAX defines types of the memory accesses permitted on various address ranges within DSP C66x CorePac 32-bit address map.
The DSP_XMC_CTRL also instantiates program and data prefetch buffer logic to reduce time during servicing read requests from the L1D, L1P and L2 memory controllers. The aim is to buffer program and data fetches from external L3_MAIN memory locations. While the program prefetch buffer is organized as 4 entry x 32 byte, the data prefetch buffer is organized in 8 slots, with 128 bytes per slot. The DSP_XMC_CTRL prefetch reduces the penalty associated with accesses to the L3_MAIN SDRAM upon L1P, L1D and L2-cache read-misses.
the DSP_XMC_CTRL registers are part of the DSP_ICFG space, hence they are not accessible outside the DSP C66x CorePac (visible only to the C66x CPU).
In summary the DSP_XMC_CTRL provides :
The device DSP subsystem does NOT use the DSP C66x CorePac multicore shared memory controller (MSMC) port to add more static RAM within subsystem boundaries, i.e. no additional SRAM is available in the DSP except for the L1P, L1D and L2 memories. Only the DSP_XMC_CTRL controller MDMA port on the L3_MAIN interconnect is used to extend DSP available RAM memory via a direct or DSP_MMU0 translated access to the device EMIF DDR memories and OCMC RAMs.
Only the memory protection function of the DSP_XMC_CTRL MPAX unit is intergated and used in the device DSP subsystem. The MDMA port 32-bit to 36-bit address extension function is NOT used in the device DSP because L3_MAIN address bus width is 32-bit. The DSP_MMU0 does NOT perform an address size (32b -> 36b) extension as well.
The XMC functionalities / registers are fully described in the section Extended Memory Controller (XMC) of the TMS320C66x DSP CorePac User Guide, ( SPRUGW0C).