Using persistent memory to fully access smart car functions

Let's say eight months ago you drove onto a highway ramp with a sharp curve. Because you were going too fast to make the turn, the car automatically took active safety and suspension measures to avoid going off the road.

Active safety measures include vehicle braking, electronic stability control and seat belt pretensioning. Smart cars can remember the active safety measures they have taken as well as the speed, GPS position and bearing conditions at the time.

Now suppose your spouse is driving on the aforementioned ramp, but this time it is raining. By recalling the ramp location and vehicle bearing conditions memorized 8 months ago, and knowing how slippery the current road conditions are, the smart car can take the correct measures in advance to prevent the car from sliding off the ramp and hitting an oncoming truck.

The above examples show total recall in action: a smart car is able to use data from different input sources, including previous experience data, to implement applications such as safety measures or customized applications for passengers.

Smart cars also need memory

Cars are becoming smarter. Whether it's navigation systems, entertainment systems, electronic stability control and active safety measures, the embedded processing capabilities of vehicles are constantly improving. According to Gartner Dataquest, by 2014, the cost of electronic components will account for 30% of the cost of new cars, and semiconductor devices will account for an increasing share of this. Most of these automotive systems process information based on current status rather than historical data. We can imagine that a large number of intelligent operations can be achieved using built-in permanent storage.

Today's cars generally have some type of persistent storage, but it's far from fully accessible. Persistent storage includes magnetic storage devices like hard drives, nonvolatile solid-state memory, or SRAM that remains connected to power when the car's engine is turned off.

Comprehensive call for customized functions

The biggest challenge facing designers is how to design a car that can use persistent memory to achieve product differentiation. When smart cars have sufficient persistent memory, customization is an area that can be fully developed. Customization can be applied to certain user interfaces or to places that are invisible to users - the working state of the car.

Many customization parameters can be set explicitly by the user, such as mirror or seat adjustment positions. Other customizations may be based on experience, such as remembering hazardous road conditions or an individual's unique driving characteristics. Any experience-based customization system should allow the user to easily modify, reset, or cancel the car's learning of a particular process.

Many customizations require the electronics to be able to recognize each person in the vehicle so that the electronics can provide full customization. Applications that increase the need for persistent storage and make full recall customization a reality include:

1. Engine and drive train performance, including aging parameters, fuel efficiency, injection and error codes, etc. Performance can also be personalized for each driver;

2. Passenger comfort, including remembering the driver or passenger settings for seat position, mirror position, temperature, and even selectable dashboard display content. For example, one driver may like to display the tachometer on a customizable display cluster or head-mounted display (HUD), while another driver prefers to display the clock;

3. Navigation assistance systems feature GPS mapping of landmark points of interest. For example, display settings like map clarity level or road congestion reports can be personalized for each driver. The navigation function can also be used to record and remind parents about their children's driving habits;

4. Active safety measures include electronic stability control and traffic sign recognition that provides information on traffic signs in different countries;

5. Rear-seat entertainment screens with parental controls that can determine viewing priorities based on the content being screened and the passengers.

In the combination of the above application areas, active safety measures initiated by the electronic stability control function, for example, can use GPS information stored from previous experience. Currently, active safety programs can only react based on current data and do not process previous experience data.

If automotive designs are to take full advantage of the increasing use of electronics every year, the capacity of permanent memory must increase accordingly. The need to store custom setup data and information in automotive memory is becoming increasingly pressing, and it must retain its contents even when the vehicle battery is disconnected.

Each application system in a smart car consists of a processing node that is connected to other processing nodes in the car. Adding available permanent memory to the interconnected network nodes will form a network of experience nodes (Figure 1). These experience nodes allow the car to customize settings, such as processing and executing actions based on the system's previous experience.

Figure 1: Distributed use of persistent storage to enable experience-based customization

Comprehensive call for car safety

Garnter said the next major growth area for automotive safety is active safety electronics. The company predicts that 50% of new cars will be equipped with electronic stability control systems (ESC). The forecasts for traction control systems (TCS), brake assist systems (BA) and adaptive navigation control systems are roughly the same.

It is well known that the pre-crash information available to these systems will help prevent catastrophic car accidents. Current systems may only have a fraction of a second to analyze and react to unexpected situations. Providing useful information to these systems as early as possible can make their preventive effects more successful. Instant information comes from sensors such as millimeter wave radar, tilt and yaw sensors, traction and transmission control, etc. Comprehensive call requires the collection of instant information as well as data from previous experience, such as the driver's reaction ability and previous sensor and ESC action data obtained at a specific GPS position and orientation.

Knowing what information to store is just as important as being able to retrieve it. It is impractical to store too much information for later use, and only important events should be stored in permanent storage.

Figure 2: Next-generation automotive safety electronics

Comprehensive call implementation

For large amounts of data used by entertainment systems, a hard disk may be used as the storage medium. Other systems in the car may use nonvolatile memory or SRAM with a constant power supply. Many vehicles use SRAM to store settings such as radio station assignments, but all stored information is lost when the car battery is disconnected. Permanent storage is best implemented using true nonvolatile memory such as flash memory.

As more and more semiconductor devices are integrated into automobiles, the use of FPGAs has increased accordingly. FPGAs usually come with non-volatile memory, whether they are on-chip flash-based FPGAs or SRAM-based FPGA devices that use external boot memory. When the power is turned off, SRAM-based FPGAs will lose this configuration information, including any new custom data. Therefore, any newly acquired custom data must be stored off-chip.

If small size or instant-on performance are design priorities, then an FPGA with on-chip flash memory is a good choice. There are also FPGA devices that embed both flash memory and SRAM in a single chip. These devices combine the protected instant-on performance of CPLDs with the speed and capacity advantages of SRAM FPGAs. These devices do not require the use of external memory to implement the SRAM startup configuration or preload the internal embedded RAM block (EBR). A feature of the new generation of non-volatile FPGA devices, such as the LatticeXP2 FPGA family, is the ability to write the contents of the internal SRAM EBR memory block back to flash memory, which becomes the default information when the device is next powered up (Figure 3). If a soft processor is used in the FPGA, the variable information in the EBR can also be written back to flash memory.

Figure 3: LatticeXP2 FPGA with flash memory that can be used to store setup information.

For SRAM-based FPGAs, the SPI flash memory used for boot programming can also be used to store custom data. Since the extra bits in SPI memory are relatively cheap and do not take up additional board area, it makes sense to use SPI memory for data storage.

To meet automotive requirements, it is important to ensure that the FPGA is AEC-Q100 qualified and that the supplier is TS16949 certified. As with any flash device, the design must consider the number of writes the device supports. For example, a flash device with a guaranteed minimum of 10,000 writes can last more than 27 years if written once a day. The life of any flash device can be extended by prudent use of the flash.

Quick start car

As electronic systems become more complex, boot times are becoming slower and slower. To maintain fast boot performance, nonvolatile FPGAs are designed with wide bandwidth paths from on-chip flash to programming SRAM distributed throughout the architecture (Figure 4). This approach allows the FPGA to complete the initialization boot process in about 1ms. SRAM-based FPGAs require hundreds of milliseconds to complete the boot process. This is important because smart car systems must initialize all nodes and networks before use. Fast boot is essential for full call success.

Figure 4: FPGA devices with flash write-back capabilities enable fast programming and high security

Other important memory options

Other permanent storage includes removable solid-state memory and onboard hard disks, which can be customized for applications that require high storage capacity, such as entertainment content or navigation systems. For example, you can plan your journey on a PC using powerful online point-of-interest search and map assistance, and then transfer the information to the car with a plug-in flash drive or Bluetooth storage device. These storage devices can also be used to store or transfer information from the car.

This article describes several methods that can be used to make automotive electronic systems more customizable and better at leveraging experience data. This article recommends using experience-based customization methods and distributed persistent memory technology. Full recall can be defined as the ability to recall information from persistent memory that will be used in conjunction with current sensor input data for the smart car.