The information below is taken from MDK v.0.2
Figure below illustrates the interfaces that enable module to module communication on an Ara phone. The network architecture centers around the MIPI M-PHY and UniPro protocols. MPHY and UniPro are specifically designed for mobile devices with advanced features to provide high throughput with low power consumption. These protocols enable modules to communicate with one another module through a packet-switched network in the Endoskeleton.
Figure above shows various example modules: an AP module with native M-PHY and UniPro, a Display module communicating via a UniPro-based protocol, a Camera module communicating via CSI-3, and a Storage Module communicating via UFS (CSI-3 and UFS are both UniProcompatible MIPI standards, and other M-PHY and UniPro compliant modules are also envisioned). Figure above shows a Medical module with a Personal Diagnostic Sensor with built-in M-PHY and UniPro support. Modules without native M-PHY and UniPro support may utilize General Purpose (GP) Bridge or High-Speed (HS) Bridge ASICs that intermediate between UniPro and several standard chip-to-chip protocols including SDIO, USB, UART, I2C, I2S, and GPIO. Each interface block provides a 2-lane bidirectional M-PORT (2 TX and 2 RX M-PHY lanes). Some modules may have additional interface blocks (up to 2 in a 2×2 and up to 4 on a front module), enabling up to four 2-lane bidirectional M-PORTS (or 8 M-PHY lanes total).
The modules in figure above connect to a UniPro switch in the Endo over a contactless media converter, which is described in the following section. A supervisory controller in the Endo manages its internal functions and external interfaces, including the UniPro switch, EPMs, and Endo battery.
MDK 0.2: All prototype modules today use either Toshiba High-Speed (HS) Bridge or General Purpose (GP) Bridge ASICs to intermediate between UniPro and several native interfaces. Developers should note that the Toshiba Bridge ASICs are not strictly required to compose a module; developers may use any suitable means to implement a M-PHY and UniPro compliant interface to the Endo. Other Bridge ASICs and M-PHY/UniPro ASICs in additional to the current Toshiba ASICs are envisioned in the future. The module templates and prototype reference modules in the Mechanical section of the MDK describe the current Bridge ASICs and associated circuitry to instantiate a module that can communicate over one of the provided bridged interfaces. The list of such bridged interfaces is provided in the Network Hardware section.
The prototype differs from the objective system in two key aspects, as illustrated in figure below. First, the prototype uses electrical contact pads instead of contactless inductive pads. Second, each interface block must utilize all four M-PHY lanes (2 RX and 2 TX) due to a limitation in the current UniPro switch.
The Ara network protocol stack is summarized in table below. The Ara network is packetswitched and based on the MIPI M-PHY and UniPro standards. The network enables high data rate communication between modules with low pin count and low power consumption.
MDK 0.2: The prototype network stack diGers from the objective system is several aspects. Layer 1 is standard MIPI M-PHY, without the contactless media converter. The current prototype also does not yet support UniPro class drivers at Layers 5-7. The current prototype uses devicespecific drivers for each prototype module; these drivers use bridged PHY protocols (as defined within the Greybus Specification) to communicate with their associated modules. The Software section describes Android features that expose these interfaces to higher layers of the stack.