SPRUJ28E November 2021 – September 2024 AM68 , AM68A , TDA4AL-Q1 , TDA4VE-Q1 , TDA4VL-Q1
VBUS (VBUSM and VBUSP) is the device interconnect communication protocol. The letter "C" in "VBUSM.C" stands for Coherence Extension and denotes the interface is dedicated to COMPUTE_CLUSTER0. The VBUS protocol is beyond the scope of the device documentation as it is purely hardware oriented. For details about the device interconnect and the associated software controls, see System Interconnect.
The MSMC2DDR bridge supports two threads on the VBUSM.C interface. They are as follows:
HPT has priority over LPT. Therefore, the execution of commands from the command FIFO can be out-of-order. As a result, the read data can also be returned out-of-order. This ensures that the HPT will be guaranteed execution even when LPT is fully blocked.
The MSMC2DDR bridge maintains data coherency across threads. Therefore, any HPT transactions that depend on the LPT transactions due to address conflicts are blocked until execution of the corresponding LPT transactions. This might result in a scenario where HPT can be blocked because of blockage on LPT. Once the LPT blockage has cleared, the blockage on the dependent HPT commands is also cleared.
HPT transactions can use global credits as well as thread 2 credits. LPT transactions can only use global credits.
On the command interface, the MSMC2DDR bridge gives back global credits on the VBUSM.C interface only if the available credits on the command queue in the DDR controller are greater than the DDRSS_V2A_CTL_REG[16-12] CRIT_THRESH field.
On the read data return interface, HPT traffic is prioritized over LPT traffic. The MSMC2DDR bridge sends HPT read data if there is at least 1 global or 1 thread 2 credit available.
The MSMC2DDR bridge sends LPT read data if there is no HPT data to send, and: