4 designs tips for AVB in-car infotainment

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AVB is clearly the choice of several automotive OEMs, says Gordon Bechtel, CTO, Media Systems, Harman Connected Services.

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Audio Video Bridging (AVB) is a well-established standard for in-car infotainment, and there is a significant amount of activity for specifying and developing AVB solutions in automobiles. The primary use case for AVB is interconnecting all devices in a vehicle’s infotainment system. That includes the head unit, rear-seat entertainment systems, telematics unit, amplifier, central audio processor, as well as rear-, side- and front-view cameras.

The fact that these units are all interconnected with a common, standards-based technology that is certified by an independent market group — AVnu — is a brand new step for the automotive OEMs. The AVnu Alliance facilitates a certified networking ecosystem for AVB products built into the Ethernet networking standard.

According to Gordon Bechtel, CTO, Media Systems, Harman Connected Services, AVB is clearly the choice of several automotive OEMs. His group at Harman develops core AVB stacks that can be ported into car infotainment products. Bechtel says that AVB is a big area of focus for Harman.

AVB Design Considerations

Harman Connected Services uses Atmel’s SAM V71 microcontrollers as communications co-processors to work on the same circuit board with larger Linux-based application processors. The software firm writes codes for customized reference platforms that automotive OEMs need to go beyond the common reference platforms.

Based on his experience of automotive infotainment systems, Bechtel has outlined the following AVB design dos and don’ts for the automotive products:

1. Sub-microsecond accuracy: Every AVB element on the network is hooked to the same accurate clock. The Ethernet hardware should feature a time stand to ensure packet arrival in the right order. Here, Bechtel mentioned the Atmel | SMART SAM V71 MCU that boasts screen registers to ensure advanced hardware filtering of inbound packets for routing to correct receive-end queues.

2. Low latency: There is a lot of data involved in AVB, both in terms of bit rate and packet rate. AVB allows low latency through reservations for traffic, which in turn, facilitate faster packet transfer for higher priority data. Design engineers should carefully shape the data to avoid packet bottlenecks as well as data overflow.

Bechtel once more pointed to Atmel’s SAM V71 microcontrollers that provide two priority queues with credit-based shaper (CBS) support that allows the hardware-based traffic shaping compliant with 802.1Qav (FQTSS) specifications for AVB.

3. 1588 Timestamp unit: It’s a protocol for correct and accurate 802.1 AS (gPTP) support as required by AVB for precision clock synchronization. The IEEE 802.1 AS carries out time synchronization and is synonymous with generalized Precision Time Protocol or gPTP.

Timestamp compare unit and a large number of precision timer counters are key for the synchronization needed in AVB for listener presentations times and talker transmissions rates as well as for media clock recovery.

4) Tightly coupled memory (TCM): It’s a configurable high-performance memory access system to allow zero-wait CPU access to data and instruction memory blocks. A careful use of TCM enables much more efficient data transfer, which is especially important for AVB class A streams.

It’s worth noting that MCUs based on ARM Cortex-M7 architecture have added the TCM capability for fast and deterministic code execution. TCM is a key enabler in running audio and video streams in a controlled and timely manner.

AVB and Cortex-M7 MCUs

The Cortex-M7 is a high-performance core with almost double the power efficiency of the older Cortex-M4. It features a six-stage superscalar pipeline with branch prediction — while the M4 has a three-stage pipeline.  Bechtel of Harman acknowledged that M7 features equate to more highly optimized code execution, which is important for Class A audio implementations with lower power consumption.

Again, Bechtel referred to the SAM V71 MCUs — which are based on the Cortex-M7 architecture — as particularly well suited for the smaller ECUs. “Rear-view cameras and power amplifiers are good examples where the V71 microcontroller would be a good fit,” he said. “Moreover, the V71 MCUs can meet the quick startup requirements needed by automotive OEMs.”

The infotainment connectivity is based on Ethernet, and most of the time, the main processor does not integrate Ethernet AVB. So the M7 microcontrollers, like the V71, bring this feature to the main processor. For the head unit, it drives the face plate, and for the telematics control, it contains the modem to make calls so echo cancellation is a must, for which DSP capability is required.

Take the audio amplifier, for instance, which receives a specific audio format that has to be converted, filtered and modulated to match the requirement for each specific speaker in the car. This means infotainment system designers will need both Ethernet and DSP capability at the same time, which Cortex-M7 based chips like V71 provide at low power and low cost.

What is real SAM V71 DSP performance in automotive audio?

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The integrated FPU DSP (into the Cortex-M7 core) is using 2X the number of clock cycles when compared with the SHARC21489.

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Thinking of selecting an ARM Cortex-M7-based Atmel SAM V70/71 for your next automotive entertainment application? Three key reasons to consider are the clock speed of the the Cortex-M7 (300 Mhz), the integration of a floating point (FPU) DSP, and last but not least, because the SAM V70/71 has obtained automotive qualification. If you delve deeper into the SAM V70/71 features list, you will see that this MCU is divided into several versions integrating Flash: 512 KB, 1024 KB or 2018 KB. And, if you compare with the competition, this MCU is the only Cortex-M7 supporting the 2 MB Flash option, being automotive qualified and delivering 1500 CoreMark — thanks to the 300 MHz clock speed when the closest competitor only reach 240 MHz and deliver 1200 CoreMark.

In fact, what makes the SAMV70/71 so unique is its FPU DSP performance. Let’s make it clear for the beginning, if you search for pure DSP performance, it will be easy to find standard DSP chip offering much higher performance. Take the Analog Device AD21489 or Blackfin70x series, for example. However, the automotive market is not only very demanding, it’s also a very cost sensitive market as well.

Think about this simple calculation: If you select AD21489 DSP, you will have to add external flash and a MCU, which would lead the total BOM to be four to five times the price associated with the SAM V71. (Let’s also keep this AD21489 as a reference in terms of performance, and examine DSP benchmark results, coming from third party DSP experts DSP Concept.)

Before analyzing the results, we need to describe the context:

• FIR is made on 256 samples block size
• Results are expressed in term of clock cycles (smaller is better)
• All DSP are floating-point except Blackfin
• Clock cycles count is measured using Audio Weaver

To elaborate upon that even further, this FIR is used to build equalization filter — the higher Taps count, the better. If we look at the “50 Taps” benchmark results, the SAM V71 (Cortex-M7 based) exhibits 22,734 clock cycles (about three times more than the SHARC21489). Unsurprisingly, the Cortex-M4 requires 50% more, but you have to integrate a Cortex-A15 to get better results, as both the Cortex-A8 and Cortex-A9 need 30% and 40% more cycles, respectively! And when looking at standard Analog Devices Blackfin DSP, only the 70x series is better by 35%… the 53x being 30% worst.

Now, if you want to build a graphic equalizer, you will have to run Biquad. For instance, when building eight channels and six stages graphic equalizer, your DSP will have to run 48 Biquad.

Again, the context:

• Biquad is made on 256 samples block size
• Results are expressed in term of clock cycles (smaller is better)
• All DSP are floating-point except Blackfin
• Clock cycles count is measured using Audio Weaver

In fact, the results are quite similar to those of the FIR benchmark: only the Cortex-A15 and the SHARC21489 exhibits better performance. The integrated FPU DSP (into the Cortex-M7 core) is using twice the amount of clock cycles when put side-by-side with the SHARC21489. If you compare the performance per price, the Cortex-M7 integrated in the SAMV71 is 50% cheaper! Using a SHARC DSP certainly makes sense if you want to build high performance home cinema system, but if you target automotive, it’s much more effective to select a FPU DSP integrated together with Flash (512KB to 2MB) and a full featured MCU.

The Atmel SAM V71 is specifically dedicated to support automotive infotainment application, offering Dual CAN and Ethernet MAC support. Other notable specs include:

• 10/100 Mbps, IEEE1588 support
• 12 KB SRAM plus DMA
• AVB support with Qav & Qas HW support for audio traffic support
• 802.3az Energy efficiency support
• Dual CAN-FD
• Up to 64 SRAM-based mailboxes
• Wake up from sleep or wake up modes on RX/TX

Don’t forget that when looking to construct an automotive high-end radio, you still need room for Ethernet MAC and AVB support… What’s more, the SAM V71 only consume 68% of the DSP resource, leaving well enough space for both AVB and Ethernet MAC.

Interested? Explore the Atmel | SMART SAM V ARM Cortex-M7 family here. More information about the the DSP benchmark can be also found on DSP Concept’s website.  Also, be sure the detailed DSP Concept’s audio processing benchmarks.

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This post has been republished with permission from SemiWiki.com, where Eric Esteve is a principle blogger as well as one of the four founding members of SemiWiki.com. This blog first appeared on SemiWiki on May 6, 2015.

Single chip MCU + DSP architecture for automotive = SAM V71

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Automotive apps are running in production by million units per year, and cost is a crucial factor when deciding on an integrated solution.

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It’s all about Cost of Ownership (CoO) and system level integration. If you target automotive related application, like audio or video processing or control of systems (Motor control, inverter, etc.), you need to integrate strong performance capable MCU with a DSP. In fact, if you expect your system to support Audio Video Bridging (AVB) MAC on top of the targeted application and to get the automotive qualification, the ARM Cortex-M7 processor-based Atmel SAMV70/71 should be your selection: offering the fastest clock speed of his kind (300 MHz), integrating a DSP Floating Point Unit (FPU), supporting AVB and qualified for automotive.

Let’s have a closer look at the SAM V71 internal architecture, shall we?

A closer look at Atmel | SMART ARM based Cortex M7 – SAMV71 internal architecture.

When developing a system around a microcontroller unit, you expect this single chip to support as many peripherals as needed in your application to minimize the global cost of ownership. That’s why you can see the long list of system peripherals (top left of the block diagram). Meanwhile, the Atmel | SMART SAM V71 is dedicated to support automotive infotainment application, e.g. Dual CAN and Ethernet MAC (bottom right). If we delve deeper into these functions, we can list these supported features:

• 10/100 Mbps, IEEE1588 support
• MII (144-pin), RMII (64-, 100, 144-pin)
• 12 KB SRAM plus DMA
• AVB support with Qav & Qas HW support for Audio traffic support
• 802.3az Energy efficiency support
• Dual CAN-FD
• Up to 64 SRAM-based mailboxes
• Wake up from sleep or wake up modes on RX/TX

The automotive-qualified SAM V70 and V71 series also offers high-speed USB with integrated PHY and Media LB, which when combined with the Cortex-M7 DSP extensions, make the family ideal for infotainment connectivity and audio applications. Let’s take a look at this DSP benchmark:

ARM CM7 Performance normalized relative to SHARC (Higher numbers are better).

If you are not limited by budget consideration and can afford integrating one standard DSP along with a MCU, you will probably select the SHARC 21489 DSP (from Analog Devices) offering the best-in-class benchmark results for FIR, Biquad and real FFT. However, such performance has a cost, not only monetarily but also in terms of power consumption and board footprint — we can call that “Cost of Ownership.” Automotive apps are running in production by million units per year, and cost is absolutely crucial in this market segment, especially when quickly deciding to go with an integrated solution.

To support audio or video infotainment application, you expect the DSP integrated in the Cortex-M7 to be “good enough” and you can see from this benchmark results that it’s the case for Biquad for example, as ARM CM7 is equal or better than any other DSP (TI C28, Blackfin 50x or 70x) except the SHARC 21489… but much cheaper! Good enough means that the SAMV70 will support automotive audio (Biquad in this case) and keep enough DSP power for Ethernet MAC (10/100 Mbps, IEEE1588) support.

Ethernet AVB Architectures (SAM V71)

In the picture above, you can see the logical SAM V71 architectures for Ethernet AVB support and how to use the DSP capabilities for Telematics Control Unit (TCU) or audio amplifier.

Integrating a DSP means that you need to develop the related DSP code. Because the DSP is tightly integrated into the ARM CM7 core, you may use the MCU development tools (and not specific DSP tools) for developing your code. Since February, the ATSAMV71-XULT (full-featured Xplained board, SAM V71 Xplained Ultra Evaluation Kit with software package drivers supporting basic drivers, software services, libraries for Atmel SAMV71, V70, E70, S70 Cortex-M7 based microcontrollers) is available from Atmel. As this board has been built around the feature-rich SAM V71, you can develop your automotive application on the same exact MCU architecture as the part going into production.

Versatility and Integrated DSP built into the ARM CM7 core allows for MCU development tools to be used instead of having to revert to specific DSP tools. You can develop your automotive application on exactly the same MCU architecture than the part going into production.

Interested? More information on this eval/dev board can found here.

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This post has been republished with permission from SemiWiki.com, where Eric Esteve is a principle blogger as well as one of the four founding members of SemiWiki.com. This blog first appeared on SemiWiki on April 29, 2015.

Atmel’s new car MCU tips imminent SoC journey

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The fact that these MCUs are targeting highly-sophisticated connected car applications like infotainment and ADAS means that the journey toward bigger and more powerful chips is now inevitable.

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The automotive industry has reached a new era marked by giant initiatives like infotainment, connected car and semi-autonomous vehicles. And, no one seems more excited than the MCU guys who have been a part and parcel of in-car electronics for the past two decades. However, the humble microcontroller is going through a profound makeover in itself in order to come to terms with the demands of the connected car environment.

Take Atmel Corporation, one of the top MCU suppliers, who has launched its SAM DA1 family of microcontrollers at Embedded World 2015 in Nuremberg, Germany. The automotive-grade ARM Cortex-M0+-based MCUs come with capacitive touch hardware support for human-machine interface (HMI) and local interconnect network (LIN) applications. The SAM DA1 series integrates peripheral touch controller (PTC) for capacitive touch and eliminates the need for external components while minimizing CPU overhead. The feature is aimed at capacitive touch button, slider, wheel and proximity sensing applications.

Moreover, SAM DA1 microcontrollers offer up to 64KB of Flash, 8KB of SRAM and 2KB read-while-write Flash. The other key features of SAM DA1 series include 45 DMIPS and up to six serial communication interface (SERCOM), USB and I²S ports. SERCOM is configurable to operate as I²C, SPI or USART, which gives developers flexibility to mix serial interfaces and have greater freedom in PCB layout.

Atmel | SMART SAM DA1 ARM based Cortex-M0+ microcontrollers

The automotive-grade MCUs — operating at a maximum frequency of 48MHz and reaching a 2.14 Coremark/MHz — are qualified to the AEC Q-100 Grade 2 (-40 to +105degreeC). According to Matthias Kaestner, VP of Automotive at Atmel, the company is targeting the SAM DA1 chips for in-vehicle networking, infotainment connectivity and body electronics.

Automotive touch surface demo at Embedded World 2015

The fact that the SAM DA1 devices are based on powerful ARM cores clearly shows a trend toward more performance and the ability to run more tasks on the same MCU. The Cortex-M0+ processor design comes with a two-stage pipeline that improves the performance while maintaining maximum frequency. Moreover, it supports a new I/O interface that allows single cycle accesses and enables faster I/O port operations.

That’s no surprise because the number of electronic control units (ECUs) is on the rise amid growing momentum for connected car features like advanced driver assistance systems (ADAS). However, a higher number of ECUs will make the communication among them more intense; so automotive OEMs want to reduce the number of ECUs while they want more value from the MCU.

Moreover, car vendors want to bring down the number of ECUs to avoid complexity within the larger car network. The outcome of this urge is the integration of more performance and functionality onto the MCU. Each ECU has at least one microcontroller.

Atmel and the Evolution of MCU

Atmel’s SAM DA1 device is another testament that the boundaries between MCU and SoC platforms are blurring. The fact that these MCUs are targeting highly sophisticated connected car applications like infotainment and ADAS means that the journey toward bigger and more powerful chips is now inevitable.

Atmel is an MCU company, and this product line has played a crucial role in its transformation that started in the late 2000s. At the same time, however, the San Jose, California–based chipmaker seems fully aware of the critical importance of the system-level solutions. Atmel calls the SAM DA1 family of chips MCUs; however, its support for more peripherals, larger memories and intelligent CPU features show just how much the MCU has changed over the course of a decade.

Memory Protection Unit in Cortex-M0+

Atmel has a major presence in the automotive market with its MCUs and touch controllers being part of the top-ten car vendors. It’s interesting to note that, beyond its MCU roots, Atmel has a lot of history in automotive electronics as well. Atmel was one of the first chipmakers to enter the automotive market.

Moreover, Atmel bought the IC division of Temic Telefunken Microelectronic GmbH for approximately $110 million back in 1998. Telefunken was an automotive electronics pioneer with an early success in electronic ignition chips that made way into Volkswagen cars back in 1980.

The release of SAM DA1 series marks a remarkable opportunity as well as a crafty challenge for Atmel in the twilight worlds of MCU and automotive electronics. Tom Hackenberg, a senior analyst at IHS, calls the phenomenon ‘SoC on wheels.’

Hackenberg says that the automotive industry consumed approximately a third of all MCUs shipped in 2013. However, now there is an SoC on the road, the brain behind the connected car, and it commands a deeper understanding of the AEC-Q100 standard for automotive quality and ISO 26262 certification for car’s functional safety.

Atmel’s AvantCar touchscreen demo at the CES 2015

The integration of touch controller into SAM DA1 chips can be an important value proposition for the car OEMs who are burning midnight oil to develop cool infotainment platforms for their newer models. Next, while AEC Q100 Grade 2 qualification is a prominent part of the SAM DA1, Atmel might have to consider augmenting the ISO 26262 certification for functional safety, a vital requirement in ADAS and other connected car features.

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Majeed Ahmad is author of books Smartphone: Mobile Revolution at the Crossroads of Communications, Computing and Consumer Electronics and The Next Web of 50 Billion Devices: Mobile Internet’s Past, Present and Future.