Meeting Storage Requirements for In-Vehicle Computing
Our cars are getting ever more electronically sophisticated every day, as in vehicle entertainment/infotainment (IVI) systems, vehicle control systems, and advanced driving assistance systems (ADAS) grow in number and capability with each new model year. The storage technology underlying these systems is increasingly solid state in nature, but is the same flash storage used in our smartphones, tablets, and laptops suitable for the automotive environment? We look at some major trends in vehicle computing—vehicle infotainment and advanced driving assistance systems (ADAS) —and consider what is needed of the storage technology used in these applications.
Advanced Driving Assistance
Today’s ADAS technologies go way beyond parking assistance and rear-view cameras, promising to reduce car accidents, improve traffic conditions, and make us all safer and better drivers. Features such as traffic sign recognition, pedestrian recognition, collision avoidance or even fully automated valet parking blur the line between cars and autonomous vehicles.
The most recent ADAS technologies, such as V2X communication, promise to go beyond single-vehicle intelligence, communicating with roadside traffic lights and other vehicles to give us superhuman awareness of road conditions, helping us avoid car accidents, traffic, and other hazards outside of our range of vision. These driving enhancement systems provide a safer and more convenient driving experience, and for OEMs they represent a huge opportunity to differentiate their vehicles through superior safety features and driving convenience.
ADAS systems depend on the processing of large amounts of data—both from vehicle sensors and networked resources. The storage and memory products that underlie these technologies must have sufficient capacity, but more important, must have extreme reliability as ADAS systems directly influence the driving experience. Data errors have an impact not only on vehicle performance but passenger safety.
In-Vehicle Entertainment Systems
The centerpiece of the modern automotive experience is the In-Vehicle Entertainment system. Often accessed through a combination of touchscreen and physical dials on the dashboard and steering wheel, it houses GPS navigation, music and video entertainment. Increasingly, it also acts as a user interface for the rest of the vehicle’s subsystems.
A great example of this kind of integrated infotainment system comes in Tesla’s Model S, which features a huge 17” touchscreen display. It combines Google Maps navigation and media player capability with a full featured web browser, energy usage and mileage charts, advanced vehicle controls and more. Model S drivers can browse the Internet, enjoy crystal clear rear-view camera displays, control how much their sunroof opens and adjust the height of their vehicle suspension all from the touchscreen. These advanced in vehicle entertainment systems rival desktop computers in processing power and capability, and the storage they use needs to be able to provide the instant-on, highly reliable functionality users expect from all their automotive controls.
When compared with other vehicle computing subsystems, the entertainment system needs to balance large storage capacity with a service life that extends far beyond a typical consumer laptop. Although the need for media and map storage is decreasing as music can now be streamed or shared from phones, and maps can be downloaded from the cloud, in-vehicle entertainment computers are increasing in capability and scope, entailing large software and operating system sizes, so IVI will still generally be the most storage intensive automotive computing subsystem.
While the decreased emphasis on media storage reduces the need for larger capacities, the increased integration of entertainment systems with core vehicle functionality, such as ADAS, increases the need for storage reliability.
Service Life Concerns
Compared to desktop computers and consumer electronics, automotive computing systems have much higher reliability and service life requirements. Whereas the average smartphone is expected to be used and supported for two or three years and a breakdown can mean an inability to access Facebook and check emails on the go, the average car may be in service for a decade or more and a breakdown in a critical system can lead to a serious accident.
The technology used in these automotive computing systems needs to go beyond advanced functionality and provide superb service lifetimes and reliability with minimum maintenance.
Service life and reliability concerns have a direct impact on the type of SSD used. While flash is fast and mechanically robust compared to rotating hard drives, all flash cells have a limited life span—a limited number of write operations which can be performed on them—before they wear out and cannot be reliably written to and read from anymore.
The highest grade of flash, called Single-Level Cell(SLC), uses one flash cell per bit of information for highly reliable data storage. Consumer grade Multi-Level Cell(MLC) flash divides that same flash cell into two or even three subcell bits to store more information. This efficient use of silicon means MLC costs much less than SLC, but as flash cells are subdivided, error rates increase significantly, and service lives of MLC cells can be 20 times worse than SLC cells.
One type of flash exists in-between SLC and MLC on the reliability and price spectrum. These flash drives use select MLC flash chips with strong endurance enhancing technology such as iSLC to balance cost and service life. Flash drives using this innovative storage method can often approach the service lives of SLC at a fraction of the cost.
For systems, such as IVI, which must balance high capacity storage needs with long service life, iSLC makes the most sense for flash storage. The ultra-high reliability and service life of SLC flash is overkill for storing maps and MP3s, but cheap MLC flash may not last for the life of the vehicle. iSLC also provides enough reliability to support IVI as these systems start integrating with vehicle controls and information feedback.
While navigational files in IVI systems are read more often than written to, ADAS systems are constantly updated with new roadside conditions, creating a heavy write burden on the SSD. While IVI functionality may be non-critical depending on their integration with vehicle systems, ADAS systems are often tied to core vehicle functionality and their failure can lead to safety issues. Highly reliable, high endurance storage is a must and premium grade SLC can be considered for ADAS systems processing critical information, while non-safety related ADAS systems or those with less intensive data usage patterns would be well served by iSLC flash drives.
Consumer devices handling non-critical data and which are expected to be replaced in a few years can get by using low-grade Multi-Level Cell (MLC) type flash, but automotive systems expected to be in use for many years, especially under heavy duty cycles, should strongly consider SLC and iSLC flash types.
Unlike most other computing environments, automotive computing systems need to operate extremely reliably despite an electrically noisy environment with “dirty” power conditions. Electromagnetic interference (EMI) from both inside and outside the vehicle, voltage spikes, unreliable power—these are nightmare scenarios for ordinary electronics but a daily fact for automotive electronics, which must deal with them on a constant basis and still work reliably day in and day out.
For automotive electronics, EMI is a huge concern. EMI can come from unintentional sources, such as a wiring harness acting as an antenna or emissions from the vehicle’s wired CANBUS network. Wireless connections such as Bluetooth, WiFi, and 3G/4G/LTE will also generate EMI. With the increase in automotive electronics and car connectivity, EMI sources will only grow over time.
Testing every electronic device in a car and making sure it works with every other device in that car, as well as potential external EMI sources, is an impossible task. Instead, major automotive markets require electronic components to be certified for Electromagnetic Compatibility (EMC.) In European markets, e-mark certification shows EMC compliance, while North America relies on the SAE-J1113 standard. These standards measure both emissions originating from the component as well as the component immunity to EMI from external sources. With the growth in ADAS technologies, EMC is not just a matter of compliance but vehicle safety as well.
In addition to EMI, power availability is another issue for automotive electronics and flash storage in particular. In the automotive environment, power is delivered from the car battery, which is charged by the alternator. Depending on the condition of the battery, whether the engine is on or off, and what other devices are being used, the actual voltage received by individual components can vary significantly from the battery’s rated voltage. For automotive SSDs this means the voltage they receive may not always be sufficient to maintain normal operation, and they must be well prepared for unexpected power loss situations.
Flash itself is a non-volatile memory that’s able to store data and keep it after power is lost, but it is not immune to power failure, because all modern flash drives use some kind of volatile memory as a temporary data store to accelerate performance as well as enhance endurance and reliability. If power is lost during operation, SSDs without power protection will lose critical data-in-flight, resulting in data loss, data corruption, or in worst case scenarios, a completely dead drive. For automotive applications, none of these scenarios is acceptable.
There are modern SSDs that exist with robust power protection technologies. By using power loss detection circuits, onboard backup power, and firmware technology, SSDs with iCell technology can detect power loss situations as soon as they occur and take the necessary action to save in-flight data before it’s lost. With the unreliable nature of power delivered to automotive computing systems and the critical nature of much of the data being stored, these power protected SSDs are the only kind which should be considered for use in automotive applications.
C.C. Wu is vice president of Innodisk and director of the Embedded Flash Division. He is a frequent presenter at the annual Flash Memory Summit held in Santa Clara, California and speaks on the topics of NAND Flash technology and embedded systems storage.