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→System-on-a-Chip Implementations
Most ARMv8 implementations are a System-On-a-Chip (SoC), which means that the processor cores, memory controller, interrupt controller, input/output (IO) bus adapters, and graphics system/GPU are all on a single chip. In some mobile chips, radio (WiFi/LTE/Bluetooth/GPS) systems may also be integrated into the SoC. This means that only the PHY (physical level circuits), RAM, flash, and power controller need to be added to create a fully-functioning system.
Most SoCs offer more features than are used in any one system and more features than can be exposed on the pins which are physically present on the chip. A pin multiplexor system, or PinMux, is used to select which signals are currently exposed on the SoC's pins. For example, a given group of pins could be used for an SPI serial interface, or an I<supersup>2</supersup>C serial interface, or as general-purpose input/output (GPIO) connections, but are only connected to one of those functions at a time.
In addition, a number of SoCs use high-speed serial interfaces for multiple purposes -- a pool of 40 multi-gigabit-per-second serial interfaces can be provided, for example, and it is up to the board designer to decide how many of those interfaces to use as the lanes of a PCIe bus, gigabit ethernet ports, or as SATA ports.
