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?? TODO:  I2C, similar low-level buses

5.

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x  Sensors

Discussion

CAPTURED THOUGHTS, CLEAN UP0

Sensors = Ultrasonic sensor?  Thermal imaging camera is a sensor?
Rather here we are discussing sensors such as ambient light, temperature, pressure, accelaration, IMU Intertial Measurement Unit (rotation), etc.

Accessing off-SoC sensors - this is basically done through a protocol.  Since SCMI implements a kind of protocol.  It is usually spoken from
general cores to the system controller (M3 core responsible for clocktree, power regulation, etc.) via a hardware mailbox.

Since this protocol is defined, it would be possible to reuse it for accessing sensor data quite independently of where the sensor is located.

The SCMI specification does not specify the transport, suggesting hardware mailboxes but acknowledging that this can be different.  The idea is to define how to SCMI over VIRTIO.

----Discussion

Sensors can be handled by a dedicated co-processor or the hypervisor implementation and provide the sensor data through a communication protocol.  This essentially offloads the burden of defining a "virtual hardware access" from the VM to the measuring hardware.   

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Systems Control Management Interface (SCMI) protocol was not originally defined for the virtual-sensor purpose itself, but describes a flexible and an appropriate abstraction for sensors. It is also appropriate for controlling power-management and related things.  The actual hardware access implementation is according to ARM offloaded to a "Systems Control Processor" but this is a virtual concept.  It could be a dedicated core in some cases, perhaps in others not.

TODO: Reference official SCMI spec.

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