This library contains drivers necessary to interface with the Boot and Power Management Processor (BPMP) co-processor on the NVIDIA TX2. The BPMP is responsible for handling boot and power management functions and also controls a few other devices. These devices are the clock controller, and an I2C channel.
The child devices of the BPMP are managed by sending requests to the BPMP module via inter-processor communication mechanisms which involve the Inter-VM Communication (IVC) protocol, Hardware Synchronisation Primitives (HSP) device module, and some shared memory.
The HSP module offers a number of primitives that can be used to synchronise state between the processor and the co-processors on the board. These include: - Shared mailboxes, which are essentially small data transfer buffers - Shared semaphores - Arbitrated sempahores, which are essentially semaphores that also include state to avoid busy waiting - Doorbells, which are essentially signals
The HSP driver in this library currently only supports the doorbell mechanisms. This driver is mainly used only by the BPMP driver in this library, but it can be used for other purposes as well.
Doorbells can be setup with the CPU complex/CPU subsystem (CCPLEX), Sensor Processing Engine (SPE), Safety Cluster Engine (SCE), and the Audio Processing Engine (APE) device modules. To first setup a doorbell, tx2_hsp_init() needs to be called first to initialise the HSP interfaces. Afterwards, the doorbells can to the device modules can be rung or checked by calling tx2_hsp_doorbell_ring() or tx2_hsp_doorbell_check() respectively with the right doorbell ID.
The IVC protocol is used to facilitate communication over a shared memory channel between the processor and other remote entities. The protocol functions similar to the producer-consumer pattern. The channel is split into fixed size message buffers that can be pushed or popped from the channel when messages need to be sent or received.