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Prototyping & Development boards design flows. Designed for optimum efficiency with Cortex-M processors, it features a sub-1V low-power core and it BLE radio offers leadingedge power consumption of less than 6.5mW (@1V) in active (Tx/Rx) mode and 700nW in sleep mode. Complementing these elements are the ARM Artisan standard cell, SRAM and general-purpose I/O physical IP libraries. Device, communication and lifecycle security is primarily delivered via the ARM mbed IoT Device Platform, which includes the open-source mbed OS and the mbed Device Connector Service, which handles communication with IoT end-point devices. mbed is supported by more than 50 mbed ecosystem partners offering a host of compatible components, cloud services and software tools, and has been adopted by more than 150,000 developers worldwide. The main device security aspect is primarily handled via mbed OS μVisor, which creates isolated security domains on the Cortex-M processor using its Memory Protection Unit (MPU), and communication security is handled via mbed TLS (Transport Layer Security). In many IoT applications device security must be augmented with additional features in hardware: for example, the Beetle demonstrator SoC implements ARM’s TRNG (True Random Number Generator) in hardware. Integration Implemented using a standard digital design flow and tools, the platform can enable digital design teams that have little knowhow Fig. 2: ARM IoT Device Demonstrator Platform – The “Beetle” test chip in the integration of radio or embedded flash to meet highly aggressive development timescales with minimal engineering resources. Layout guidelines are available to developers: essentially delivering integration capabilities for engineers with primarily digital experience. Including timing and physical abstract models, the use of an EDA-tool-agnostic physical design kit (PDK) significantly mitigates the challenge of radio integration – engineers do not require extensive mixed-signal/RF expertise and in fact, the BLE radio can essentially be treated as a digital IP block. Integration takes a relatively straightforward hard-macrolike approach with an all-digital interface to the host controller and standard AMBA-AHB bus interface for easy integration to the Cortex-M IoT subsystem. The asynchronous design also removes the dependency on clock timing between the radio and host control. Other features of the implementation include use of sideband signals for radio power and clock control; a built-in pad ring for the radio I/O, to simplify integration and to help the critical and noise-susceptible radio I/O. The integrator needs only to follow some basic integration guidelines to ensure sufficient noise isolation such as sufficient decoupling of the power supplies and guard-banding to avoid substrate noise. To simplify this further macro blocks of decoupling metaloxide metal (MOM) capacitors were created to provide an area efficient bulk decoupling capacitor for the supplies as well as comprehensive guidelines for guard-banding against substrate noise between the radio and digital logic. To simplify design, the radio design requires minimal external components with just seven capacitors, two inductors, two crystals and an antenna. The design also integrates embedded flash IP (from TSMC), which was a first experience of embedded flash for the design team and presented a more complex challenge than integrating SRAM blocks for example. It brings the requirement to use voltage-level shifting between the sub-1V logic domain and flash memory, which requires 1.2V/2.5V supply levels for its read/write operations. The ARM Artisan physical IP platform provides both regular and thick-oxide versions of the level shifters, required for shifting to the 2.5V domain. Even when optimised for low-power systems, the embedded flash memory accesses contribute significantly to the power consumption of the SoC, prompting the development and use of an embedded flash cache to reduce flash memory accesses to a minimum. Two banks of 128K were implemented in the Beetle test chip, which as an example could run application code in one bank with over-the-air code updates in the second. The cache and flash controller are part of the IoT subsystem, which could support up to 512K of flash for more complex nodes. Platform availability and evolution The IoT subsystem for Cortex-M together with the Cortex-M3 processor, the Cordio radio, low-power Artisan physical IP libraries, embedded Flash hard macro (through TSMC), mbed Device Platform, plus an MPS2 development board are available now for rapid software and hardware prototyping and development. The company is also looking to enrich its IoT development ecosystem to further enhance deployment and rapid prototyping of IoT devices. In conjunction with Thundersoft, ARM recently set up an IoT ecosystem accelerator in Beijing to offer workshops, training and design services to help IoT device makers from start-ups to OEMs. In addition to the IoT components that have been used in the Beetle chip, ARM is proposing further security enhancements with the TrustZone CryptoCell IP. Artisan libraries for more advanced process nodes might also be used in the future to improve energy efficiency. www.electronics-eetimes.com Electronic Engineering Times Europe February 2016 27


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