The device memory hierarchy includes four levels:
- L1 is internal to the CPUs. It concerns data exchange with the internal Level1 cache memory subsystem, and it is the closest memory to the microprocessor unit (MPU) core and the IVA core.
- L2 is included in the IPU subsystem and the MPU subsystem.
- The chip-level interconnect consists of one L3 interconnect and five L4 interconnects. It enables communication among the modules and subsystems in the device.
Figure 14-1 shows an overview of the L3 and L4 interconnect architecture.
- L3 handles many types of data transfers, especially exchanges with system-on-chip/external memories. L3 transfers data with a maximum width of 128 bits from the initiator to the target. The L3 interconnect is a little-endian platform
- The L4 is composed of the following:
- L4_CFG: Includes the majority of the firewall configuration interface for level 3 (L3) system modules and peripheral interconnect;
- L4_PER: Includes the main peripherals that require system direct memory access (sDMA) access. L4_PER has three instances L4_PER1, L4_PER2 and L4_PER3. Each of these three instances has three ports connecting it to L3_MAIN interconnect:
- L4_PER1_P1, L4_PER1_P2, L4_PER1_P3
- L4_PER2_P1, L4_PER2_P2, L4_PER2_P3
- L4_PER3_P1, L4_PER3_P2, L4_PER3_P3
Through L3_MAIN interconnect, different initiators can access each of these L4_PERx_Pi ports. For information regarding which initiator accesses which L4_PERx_Pi port, see Figure 14-3. - L4_WKUP: Includes peripherals attached to the WKUP power domain.
Modules are connected to the interconnect through an IA for the initiator module and a TA for target modules. Each module/subsystem connection is statically configured to tune the access, depending on the characteristics of the module.
To unauthorize a module or L4 interconnect access, some TAs include configurable firewalls (FWs). A firewall restricts or filters the accesses allowed to an initiator according to different access criteria. The firewalls can usually be configured by software.
The L3 and L4 interconnect default settings are fully functional; they enable all possible functional data paths and a minimal default protection setting.