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Adding Connectivity to Your Design

Microchip offers support for a variety of wired and wireless communication protocols, including peripheral devices and solutions that are integrated with a PIC® Microcontroller (MCU). Wireless connectivity options include: Wi-Fi®, Bluetooth®, 802.15.4/ZigBee® and our proprietary MiWi™ wireless networking protocol. Other connectivity protocols supported include USB (device, host, OTG and hubs), Ethernet, CAN, LIN, IrDA® and RS-485. All of these protocols are supported with free software libraries, low-cost development platforms and free samples.

www.microchip.com/connectivity The Microchip name and logo, the Microchip logo and PIC are registered trademarks and MiWi is a trademark of Microchip Technology Incorporated in the U.S.A. and other countries. All other trademarks are the property of their registered owners. © 2015 Microchip Technology Inc. All rights reserved. 1/15 DS00001742B

FROM THE EDITOR

EMBEDDED SYSTEMS ENGINEERING 2015

ARM, Intel, IP and USB

Vice President & Publisher Clair Bright

So much going on! Here’s a snapshot of what’s crossed my desk in only the last week.

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Editorial Editor-in-Chief Chris Ciufo [email protected] Managing Editor Anne Fisher [email protected] Contributing Editors Caroline Hayes Gabe Moretti Creative/Production Production Manager Stephanie Bradbury Graphic Designers Nicky Jacobson Simone Bradley Media Coordinator Kyle Barreca Senior Web Developers Slava Dotsenko Mariam Moattari Advertising / Reprint Sales Vice President, Sales Embedded Electronics Media Group Clair Bright [email protected] (415) 255-0390 ext. 15 Sales Manager Michael Cloward [email protected] (415) 255-0390 ext. 17 Marketing/Circulation Jenna Johnson To Subscribe www.eecatalog.com

Extension Media, LLC Corporate Office President and Publisher Vince Ridley [email protected] (415) 255-0390 ext. 18 Vice President & Publisher Clair Bright [email protected] Vice President, Business Development Melissa Sterling [email protected] Human Resources / Administration Darla Rovetti

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Embedded Systems Engineering is published by Extension Media LLC, 1786 18th Street, San Francisco, CA 94107. Copyright © 2015 by Extension Media LLC. All rights reserved. Printed in the U.S.

By Chris A. Ciufo, Editor-in-Chief, Embedded Systems Engineering

INTEL AND 6TH GENERATION CORE CPUS Fresh on the heels of Intel’s Broadwell (22nm) CPU refresh announcement in June comes August’s announcement of Skylake. While few material details are available, the 6600K SKU is the Core i5 and the 6700K SKU is the Core i7. Yet only the “6” at the beginning of the part number is predictable—the rest of Intel’s nomenclature has gone so far off the rails that even Intel’s trusty ark.intel.com website isn’t as useful as it once was. (I dare you to figure out Intel’s roadmap from Ark!) Meaning, for those of us not under NDA, it’s hard to tell the difference between Broadwell, Broadwell-H, and Skylake (which also has suffixes to which I’m not privy). Broadwell was actually announced in 2014 but Intel had fab process problems so it was pulled back. Yet Skylake’s schedule continued. The slightly lifted-Skylake kimono reveals that these 6th-gen Core CPUs are for high-end gaming laptops and PCs, with improved performance and a new Z170 Southbridge with loads of peripherals (though strangely not USB 3.1). It’s interesting that scores of embedded board vendors recently announced Haswell SBCs, and I assume that when the embedded versions of Skylake are announced (late Fall?) everyone will rush to then announce Skylake 6th-gen Core boards. I’m looking forward to the Intel Developers Forum 2015 in just two weeks. (Fun fact: IDF is earlier this year since I presume Intel got tired of Apple’s WWDC upstaging it.) Perhaps at IDF 2015 I’ll find that one key chart that puts all of this into context. But don’t get me started on the Atom roadmap: that one’s just as confusing. ARM’S MBED OS AND SECURITY Meanwhile over in the ARM camp, the company’s IoT strategy is unfolding like an elegant origami swan. Except I have no idea what that means. Even though last Fall’s announcement of mbed OS was mostly content-free, we know that ARM is looking to make all things IoT easy and create a cookbook for designers. As ARM’s VP Ian Drew told me: “even an artist who is not a designer should be able to create something.” mbed OS—and its related modules like μvisor and security—are designed to work together: from ARM silicon up to the application API. And ARM is dead serious about IoT security. While I notice that Intel’s McAfee (security tools) building in Santa Clara now says “Intel Security,” Intel’s security announcements aren’t coming as fast and furious as are ARM’s. In February, ARM bought IoT security company Offspark with a plan to convert PolarSSL into mbed TLS (Transport Layer Security). It should be available with mbed OS in August 2015. And as we went to press, ARM bought Israel’s Sansa Security to “embed security at every potential attack point” in the connected device chain,” said ARM’s CTO Mike Muller. For the last six months, ARM has been beefing up the company’s TrustZone IP plus creating security packages for the Cortex-R (real-time) CPUs used in transportation and control systems. I’m unclear on how Sansa’s chipsets fit with ARM’s lighter-weight IoT end node vision. USB TYPE-C The USB-IF’s Type-C either-way connector is all the rage, and you’ll be hearing more about it. I’ve written several articles on it already, and more vendors are announcing products. Synopsys has new USB Type-C IP for those designing SoCs; Pericom Semiconductor [one of our sponsors] has rolled out a whole family of switches, crossbars, and redrivers; and Lattice Semiconductor has announced plans for “SuperMHL” ICs for Type-C. SuperMHL is an open standard that lets smartphones and tablets drive 8K/120 video to high-res monitors and projectors. The MHL standard is already on 750 million devices (but not Apple products). The vision, says Lattice’s Abdullah Raouf, Sr. PMM for Wired Video Solutions, is to use Type-C’s incredible speed and alternate channels to allow a powerful mobile device to replace the laptop or desktop. Just add a USB 3.0/3.1 keyboard and mouse, and today’s mobiles easily exceed the corporate laptops people lug to meetings.

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IN THIS ISSUE

CONTENTS PCI Express Departments Brick by Brick: Q&A with PCI-SIG President and Chairman Al Yanes and PCI-SIG Board Member Ramin Neshati

From the Editor ARM, Intel, IP and USB By Chris A. Ciufo, Editor-in-Chief, Embedded; Extension Media

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RAS Data Protection Considerations for PCI Express Designs

Special Features

By Richard Solomon, Synopsys

Software Quality and the Industrial Internet of Things: Why it Matters NOW

GHz Timing Giving You the Jitters? Three Things You Need to Know

By John Paliotta, Vector Software

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By Chris A. Ciufo, Editor-in-Chief, Embedded; Extension Media

Advances in Architecture allow ARM Processors to Tackle Endpoints and Gateways, for the Cloud By Dave Bursky, Senior Editor

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By Anne Fisher, Managing Editor

Product Showcases 5

Application Solutions #PBSET Access I/O Products Inc.

USB

USB Type-C: Doing Away with a Difference Makes a Difference By Anne Fisher, Managing Editor

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Hardware

Cover Story Summing Up Circuit Protection for USB 3.0 and USB in Automotive Applications By VP Pai, ProTek Devices

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#PBSET General Standards Corporation

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%FWFMPQNFOU Teledyne LeCroy

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Is Glass Losing Its Touch? By Sri Peruvemba, Cambrios Technologies Corp.

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Product Showcases

Ethernet What’s Promising to Widen Ethernet AVB’s Scope? 32

By Caroline Hayes, Senior Editor

Hardware #PBSET Access I/O Products Inc. Teledyne LeCroy )VCT Microchip Technology

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Analog High Speed Communication Devices for 40G/100GB Ethernet Require a Totally New Approach to Test Cédric Mayor, Chief Technical Officer, Presto Engineering, Inc., Caen, France

Product Showcases

Software Middleware

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ICs $IJQT Microchip Technology

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SPECIAL FEATURE

Software Quality and the Industrial Internet of Things: Why it Matters NOW Which manufacturers are on the glide path to realizing increased productivity and more with the IIoT?

By John Paliotta, Vector Software

The International Telecommunication Union defines the Internet of Things (IoT) as a global infrastructure for the information society, enabling advanced services by interconnecting physical and virtual things based on existing and evolving interoperable information and communication technologies. What’s already clear is that in a nutshell, with every electronic device having network connectivity (see Figure), every manufacturer of electronic devices will essentially be in the software business. THE COMMON THREAD The broader Internet of Things trend generally refers to consumer applications such as wearables, home automation, kitchen appliances, etc. There has been a similar evolution in the industrial sector that embraces these concepts, known as Industry 4.0, the Fourth Industrial Revolution, or more simply, the Industrial Internet of Things (IIoT). The IIoT is more specific than the IoT, and includes the integration of complex devices and systems with networked sensors and software. According to the Industrial Internet Consortium, “The Industrial Internet is an internet of things, machines, computers and people, enabling intelligent industrial operations using advanced data analytics for transformational business outcomes. It embodies the convergence of the global industrial ecosystem, advanced computing and manufacturing, pervasive sensing and ubiquitous network connectivity.” The ability to connect these types of systems will significantly impact business operations. The IIoT can utilize the power of intelligent technologies to reinvent business processes and production methods while creating new revenue streams and transforming the modern workforce. For example, IIoT technologies are already helping to increase productivity, reduce operating costs and improve safety conditions for employees. Manufacturers are introducing increased automation and flexible production techniques to improve productivity,

Figure 1. Courtesy Vector Software.

while connected sensor networks monitor logistics to create more efficient operations and reduce costs. Embedded technology in freight applications is able to optimize routes to save fuel and reduce delivery costs, or alert relevant personnel in the event of mechanical breakdowns, saving substantial resources—and even lives. Unmanned vehicles are being used to inspect remote pipelines in harsh environments to help keep employees safe. A common thread throughout all of these applications is that they are being powered by advanced embedded software technology. IIOT: DON’T LET ME BE MISUNDERSTOOD To quote the recent “Winning with the Industrial Internet of Things” report , the Industrial Internet of Things is “arguably the biggest driver of productivity and growth in the next decade” and it will “accelerate the reinvention of sectors that account for almost two-thirds of world output.” The report states that the Industrial Internet of Things has the potential to add $14.2 trillion to the global economy by 2030. However, although early adopters are realizing the benefits of the IIoT, its widespread adoption is hampered by skepticism and lack of understanding. According to the same study, “CEOs and executives express remarkable confidence (96 percent) that the senior leadership in their organizations grasp at least something of the nature of the IIoT… but far fewer say their leaders have completely understood it (38 percent).” A similar study was conducted in collaboration with the World Economic Forum which surveyed more than 90 market leaders who are actively pursuing IIoT initiatives. The vast majority (88 percent) said that they still

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do not fully understand the underlying business models and long-term implications of the IIoT. IS INDUSTRY PREPARED FOR IOT? With the Internet of Things happening at a broad level, in every industry, there will be many new vendors providing applications, middleware and connected devices. Many of these vendors will be new to building embedded software, engineering robust software, or both. Additionally, consumers and manufacturers alike will expect the operation of the connected devices to be seamless and reliable and deliver a positive user experience in general. Consider how Apple destroyed Nokia and Blackberry. Was it with better electronic components? Not really—it was with better software, which provided a better user experience. Let’s revisit the point earlier that the transformation to an Internet of Things-enabled environment means that every manufacturer of electronic devices will essentially be in the software business. Vendors with a legacy of building mission-critical embedded software for industries like automotive and industrial controls should have a sizeable advantage in transitioning to IIoT. They have already solved many of the real-time embedded challenges for application partitioning, redundancy and long up-times. Vendors with no previous software experience, or with experience building consumer-grade software, are likely to grossly underestimate the challenges associated with supporting IIoT. In either case, as more software applications have a requirement for dependable and uninterrupted operation, vendors will need to implement processes that can deliver quality software. SOFTWARE UNDER SCRUTINY As production environments and business-critical applications continue to become more dependent on the products whose functionality is controlled by software, the quality of the software has started to come under scrutiny, particularly in situations where safety, security or human life is exposed to risk if the software fails. The biggest challenge that software developers face is balancing testing completeness with time-to-market. Often the fear is losing the “first mover advantage” for the sake of testing completeness. However, sacrificing quality for time to market is a dangerous choice that can have a significant effect on brand value. In the normal product life cycle for a software application, 1.0 is the initial release to customers. In subsequent releases, bugs are fixed, and functionality that was missing from 1.0 is released. The product typically reaches a point at which users are happy with the quality and the features of the product. The Quality Deficit sits between the first release of the product and when the market considers the product to be of good quality. Minimizing or eliminating this Quality Deficit should be high on the priority list of every organization that is building software.

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JOURNEY TO QUALITY To tackle this challenge involves addressing the second challenge that development teams face: allocating development resources between requirements, design, coding and testing. Historically, the workflow has been as follows: Most development teams place the highest priority placed on coding, with less emphasis on the Application Programming Interface (API) and test case design. Generally, groups will assign senior staff to code development and junior staff to testing. However, if this model were to be completely reversed, then the most valuable software development products would have a complete and flexible API, and the test cases prove the correctness of this API. If a great API is developed, and tests formalize the correct behavior to this API, then the actual code writing can be done by junior staff, the code can be re-factored with confidence, and quality will be greatly improved. A final challenge to address on the journey to software quality is that most groups maintain a variety of test types, and a different group in the organization “owns” each type of test. It is very common for the developers to create and maintain low-level tests, while the Quality Assurance (QA) department is responsible for the others. The QA tests are generally run only after several weeks of development, when hundreds of source changes have been integrated into the code base. This makes finding the root cause of a broken test time consuming and frustrating. The solution to this challenge is to treat test cases as a valuable asset of the organization and leverage them across the entire team and application life cycle. CONCLUSION There is an increasingly important role for software quality as the industry adapts to the Industrial Internet of Things and the fourth industrial revolution. Organizations that do not adjust their development processes to enable them to produce higher quality applications are risking not only their brand, but also their very existence. Organizations that do adapt will thrive. John Paliotta is co-founder and chief technology officer of Vector Software.

SPECIAL FEATURE

Advances in Architecture allow ARM Processors to Tackle Endpoints and Gateways, for the Cloud By Dave Bursky, Senior Editor

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he plethora of devices that connect to the cloud, and even many of the devices in the cloud, are empowered by embedded processors that deliver a wide range of performance to execute the desired tasks. The tasks range from simple endpoints that sense and collect data such as temperature, vibration, pressure, or other parameters. The endpoints, in turn, are linked to the next level via wireless or wired networks. This next level consists of more complex edge devices (gateways) that aggregate and preprocess the data collected from endpoints to reduce the quantity of data and then feed that data into the cloud, where it is routed to the appropriate server.

family, but those cores are not as suitable for real-time applications since they employ memory management units that limit the core’s ability to provide real-time deterministic behavior or respond in just a few cycles to interrupts.

To give the Cortex-M7 the performance and capabilities needed by the more demanding applications, designers crafted efficient memory interfaces such as tightlycoupled memories (TCMs) for real-time response, and Instruction and Data caches for efficient access to large memories and powerful peripherals. Additionally, EMBEDDED PROCESSORS PROVIDE INTELLIGENCE To provide the necessary “intelligence’”, higher-performance but low- direct-memory-access (DMA) into the tightly-coupled power embedded processors are needed in the endpoints. To that end, memories via the slave version of ARM’s AHB bus, and ARM has expanded its Cortex-M processor family with the addition of the AHBP to access existing AHB peripherals and memthe Cortex®-M7 processor, which delivers twice the DSP performance ories give the processor the ability to respond quickly of the previously released Cortex®-M4, but is software compatible. and handle a wide range of I/O requirements (Figure 1). Based on data from various market research organizations such as Gartner, International Data Corp., and the Semiconductor Industry Association, as well as from ARM itself, ARM’s over 200 Cortex-M series customers have shipped about 4.3 billion Cortex-M series cores in 2014, and 1.6 billion in Q1 2015. Companies such as Atmel, Freescale Semiconductor, Marvell, ST Microelectronics, Texas Instruments and many other vendors have embedded these processor cores into various microcontrollers or custom application-specific integrated circuits. The Cortex-M7 will be able to take on higher-end embedded applications in next-generation connected devices, vehicles, drones, street lighting, appliances, and many other applications where a full-blown Linux-based operating system is not required. Cortex-M7 can run IoT operating systems such as ARM-developed mbed™ OS that provide secure, reliable communications within the home or enterprise and out into the cloud. The Cortex-M7 can also run traditional embedded RTOSes for control applications. The higher performance point of the Cortex-M7 processor is well suited to intelligent end-point devices in markets such as industrial, lighter-weight access points and applications that require real-time response along with high-performance. Of course, ARM also offers still higher-performance processor cores in its Cortex A-series

Figure 1: The ARM® Cortex®-M7 processor core packs improved DSP compute capabilities as well as tightlycoupled memories and a wide array of peripheral support functions that let it deliver double the DSP performance of the M4 as well as higher overall performance. (TCM = tightly coupled memory, FPU = floating-point unit, WIC = wake-up interrupt controller, ETM = embedded trace macrocell, ECC = error checking and correction, MPU = memory protection unit.)


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The compatibility of the Cortex-M7 with previous M-series processors gives the Cortex-M7 a wide range of pre-built resources that companies can leverage to quickly develop system-on-a-chip solutions for use in endpoints, home gateways, edge devices, data aggregation hardware and many other applications. Compilers, libraries and even application code will all benefit with an easy migration from previous devices. This should shorten development times and allow SoCs that integrate the new Cortex-M7 core to be used to generate devices, possibly by the end of 2015.

endpoint, gateway and edge applications. For example, both Atmel and Freescale have crafted full generalpurpose microcontrollers around the Cortex-M7 core (the SAM70 and Kinetis families, respectively), while STMicro has developed a chip that integrates most of the functionality of a home gateway that is an offshoot of its STM32 F7 series of microcontrollers.

SOFTWARE COMPATIBILITY SHORTENS DEVELOPMENT TIME Software and hardware compatibility with previous CortexM-series processors will allow designers to reuse hours to months of software development done on the older processors to directly transfer to the Cortex-M7 core, thus greatly reducing the time to develop applications. Functions such as voice recognition, sensor fusion or performance optimiFigure 2: The STM32F7-SOM-1A Module from Emcraft zation of control applications can be directly transferred Systems provides a designer with a full starter kit for designing applications using the M7 core. In addition to the over to new designs and execute more efficiently. Embedded board, the company has ported a μClinix software package designers will find that their time spent finely optimizing to the platform. application code on older processors can be directly ported to new devices built around the enhanced Cortex-M7 core. Additionally, other development partners such as Hence the new performance enhancements of the Cortex- Emcraft Systems have crafted development kits based on the Cortex-M7. For example, the STM32F7-SOMM7 can be utilized with little or no software work. 1A Module from Emcraft is based on the STMicro The CPU core in the Cortex-M7 processor has a six-stage STM32F746 microcontroller that runs at up to 200 superscalar pipeline with branch prediction, and the DSP MHz, packs 320 kbytes of RAM and 1 Mbyte of Flash extensions allow the core to perform single-cycle 16- or (Figure 2). In addition to the MCU, the board adds 32 32-bit multiply-accumulate (MAC) operations, single-cycle Mbytes of SDRAM, 16 Mbytes of NOR flash, an Ethdual 16-bit MAC operations, as well as 8/16-bit SIMD ernet PHY and still other resources. (single-instruction/multiple-data) arithmetic. Also in the Cortex-M7 is a double-precision floating-point unit that delivers higher accuracy for applications such as required by precise positioning in the home or the enterprise and by GPS. Inside the Cortex-M7 core, instruction and data buses have been enlarged to 64 bits vs the 32-bit buses used in previous M-series processors. That enables multiple instructions to be fetched in each clock cycle. Additionally, the high performance 64-bit AXI system bus provides a system interconnect capability that is new for Cortex-M-class cores. It’s optimized for throughput by supporting multiple transactions and queuing of transactions. Attached to the AXI bus are configurable instruction and data caches that provide low-latency buffering of information as it is fetched from slower memories. The resulting architecture enhances the processor’s ability to work with external memories to handle large data arrays and programs.

“With the Cortex-M7, functions such as voice recognition, sensor fusion or performance optimization of control applications can be directly transferred over to new designs”

The microcontrollers in Atmel’s SAM70 series can operate at frequencies of up to 300 MHz and deliver over 600 DMIPS of computational throughput. The architecture allows for lower power consumption, highspeed data stream handling and the ability to handle video streams. In the future Atmel expects to migrate the processor to a 40nm process that will enhance the performance by about another 30%. The company has optimized the SAM70 microcontroller family for automotive infotainment and telematics applications by adding Ethernet AVB and MediaLB support on the chip. HIGH-PERFORMANCE MICROCONTROLLERS Advanced analog interfaces and timers will also let the LEVERAGE THE CORTEX-M7 CORE Several of the early licensees of the Cortex-M7 core include processors handle various motor control and robotics Atmel, Freescale and STMicroelectronics. These vendors applications. and others are developing microcontrollers that can tackle 6

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Designers at Freescale are also leveraging the improvements in the Cortex-M7—the enhanced pipeline supports execution of multiple instructions per clock, improving the throughput of the core. Power modes such as high-speed run mode and very low-power run mode dynamically change the power management of Kinetis devices. High-speed run mode will complete tasks as quickly as possible, while the very-low-power run mode can be used to extract more processing from the Cortex-M7 core at lower CPU speeds. HIGH SPEED CAN ACTUALLY LOWER POWER CONSUMPTION The higher processing performance can be used to perform functions in a shorter amount of time. Specifically, there are two aspects of the processing performance that will affect end applications–especially those requiring lower power consumption. First, having more capabilities per clock cycle will allow a task to be completed at lower system clock speeds. Digital filters which previously required 200 MHz to operate can now be done at 100 MHz. In addition, the computational improvements will allow designs to take advantage of low-power run modes as the improvements can be realized at all CPU speeds. Second, another strategy for low-power design is completing tasks as quickly as possible. Along with the processing throughput, the Cortex-M7 supports higher CPU speeds. So when using the new core to its fullest capabilities, time spent in active modes processing can be reduced, which will allow applications to spend more time in low-power modes. With a top clock frequency of 200 MHz, the STM32 F7 microcontrollers take advantage of the six-stage pipeline and FPU to achieve a throughput of up to 1000 CoreMarks (Figure 3). In addition to the Cortex-M7 core, designers at STMicro included two independent mechanisms to reach 0-wait-state performance from both internal and external memories: using the company’s Adaptive Real-Time (ART Accelerator™) for internal embedded Flash, and employing the L1 cache for both execution and data access from internal and external memories. Designers of the STM32 F7 optimized the entire system by integrating multiple new peripheral support functions around the Cortex-M7 processor core. Lots of timers, a crypto/hash processor, a true random number generator, multichannel DACs and ADCs, a high-throughput AXI and multi-AHB bus matrix, and many other features are all integrated on the chip (refer

Figure 3: The high-level of integration done by STMicro on its STM32 F7 microcontroller provides designers with a highly configurable solution that delivers double the performance of previous-generation M-series processors.

back to Figure 3). One of the more novel features is a large SRAM with a scattered architecture. The SRAM contains a total of 320 kbytes that is divided into a 240 kbyte and a 16 kbyte block on the bus matrix, 16 kbytes of instruction TCM RAM and 4 kbytes of backup SRAM. This scattered approach lets the large SRAM block support large data buffers and multiple software stacks, while the backup SRAM allows data retention in the lowest power modes for quick recovery, and the data and instruction TCM blocks support critical real-time data and program execution. The high performance of the Cortex-M7 and its compatibility with previous generation Cortex-M series processors gives designers a jumpstart in developing next-generation microcontrollers or SoC solutions. The ability to operate at frequencies of 200 MHz and above will actually let the processors conserve energy and lower system power consumption in many of endpoints and lightweight access points. In the future, the transition to smaller process nodes will further enhance the performance while lowering the operating power to deliver leading edge solutions in systems ranging from endpoints such as sensor nodes and smart wearables to critical monitoring and maintenance functions for intelligent edge devices and routers. This article was sponsored by ARM.


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engineers’ guide to USB

Summing Up Circuit Protection for USB 3.0 and USB in Automotive Applications As automakers continue to build more and more computing functions into cars, USB will play a big role, whether for data transfer or basic charging. By VP Pai, ProTek Devices

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ersion 3.0 of the Universal Serial Bus (USB) specification has been around now since 2008. The technology is now well established across myriad devices requiring high speed data transfer rates. One analyst firm estimated some 70 million USB 3.0 devices shipped in 2011. A further estimate claims this will balloon to more than three billion global USB 3.0 device shipments by 2018. For anyone involved in implementing USB designs, there’s a lot riding on this technology. USB is critical to computing devices that are in turn also critical to everyday business or personal use. Thus proper circuit protection against electrical transients that can break such devices is a must. But, how is it best to implement proper circuit protection for USB 3.0? Also, in general, USB plays a key role in other big applications, like automotive. So, what are some of the key considerations for USB in such an application? USB 3.0 OVERVIEW First, a review of the USB 3.0 specification is in order. USB 3.0 offered a generational leap in performance capabilities over USB 2.0. It increased data rates by 10 times. It also expanded transmission lines to three differential pairs (compared to one in the previous 2.0 standard). USB was introduced in 1996 with version 1.0. It provided 1.5Mbit/sec in low-speed (LS) mode and 12Mbit/sec in full-speed (FS) mode. In 2000 USB 2.0 entered the market. The new high-speed (HS) mode then boosted transfer speeds up to 480Mbit/sec. It was downwards compatible to low-speed and full-speed mode. The USB 2.0 interface is still widely used in consumer electronics. Billions of devices such as camcorders, digital cameras, digital music players, game consoles, DVD/Blue-Ray players and TVs use one or all of these USB standards. It’s also widespread in portable devices such as smartphones and in networking equipment like DSL/router units. When the USB 3.0 specification was released it demonstrated full USB 2.0 functionality (HS, FS, LS). It also showcased the new separate ultra-high speed data link, called SuperSpeed. The SuperSpeed link works with separate differential data lines for download (host => device, called TX direction). This is also the case for upload in RX direction (device => host). The maximum data rate in SuperSpeed mode is 5Gbit/sec. The combination of USB 2.0 functionality and the new SuperSpeed mode required new cable construction. This new construction had to serve three differential coupled signal lines (TX+/Tx-, RX+/Rx- and D+/D-). The VCC and the GND line complete the cable set.

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Figure 1. TVS Array layout recommendation in USB 3.0+2.0 application USB ENGINEERING DESIGN CONSIDERATIONS Electronics engineers must consider a host of requirements when designing-in a USB 3.0 link. For example, full impedance-matched 90-Ohm differential design for all PCB lines and interconnection cables is mandatory. In addition non-differential coupled lines have to be minimized. They have significant impact to eye pattern inner eye opening. Also, trace-width and trace-separation of the 90-Ohm differential are critical. The coupled PCB traces should not be too narrow, to avoid additional loss and to be robust enough for manufacturing. A trace-width of 0.007” (0.178mm) and a separation of 0.007” (0.178mm) between the differential traces are ideal for production. Identical delay (trace length) between the positive and the negative line (including the USB 3.0 cable) of the differential coupled link (minimizing in pair skew) is needed. This is important to keep signal integrity high and to avoid common mode reflection. FACTORING IN CIRCUIT PROTECTION A USB 3.0 standard-A connector section can easily and cost-effectively be designed in combination with appropriate electrostatic discharge (ESD) circuit protection devices. For example, the SuperSpeed TX and RX data pairs can be protected by a transient voltage suppressor array (TVS array) that is capable of protecting many data lines, such as up to four lines. The D+ D- regular USB 2.0 pair can then be protected by a TVS array designed to protect up to a couple of data lines. It would be ideal to use a TVS array

engineers’ s’ gguide uide to U USB SB

Built-In Intelligence SuperSpeed Smart Hubs Expanding System Interfaces Beyond USB

Microchip’s Smart Hub Controllers are 4-port, SuperSpeed (SS)/Hi-Speed (HS), SV^WV^LYKL]PJLZ[OH[HYLJVUÄN\YHISLHUKM\SS`JVTWSPHU[^P[O[OL