If the car audio system can play multiple CDs, such in-car entertainment systems used to be advanced system configurations. Today's in-vehicle infotainment systems are complex embedded subsystems that combine MP3 music playback, GPS navigation, voice recognition, hands-free cellular connectivity, DVD video and even Internet browsing.
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As in-vehicle infotainment systems enter a wider range of multimedia applications, its storage subsystems are playing an increasingly important role. Music and video files must be stored and quickly accessed. Large map data files for 3D GPS systems must be quickly searched and displayed, and audio files for speech recognition need to be synthesized and stored.
Most infotainment systems currently in use rely on ruggedized hard drives to store data. These devices typically provide capacities from 40GB to 50GB. As a solid and mature technology, hard drives offer several attractive advantages. At a price per GB, they present a cost-effective solution for the designer. In applications that overcome the inherent seek and spin latency of hard drives (for example, most read accesses are sequential), hard drives can deliver large amounts of data in a short amount of time. However, in the increasingly complex in-vehicle infotainment systems, other factors play an increasingly important role in the selection of storage subsystems.
In many applications, the sheer volume of data storage available on hard drives provides little benefit to in-vehicle infotainment designers, as most systems require only 4GB to 8GB of memory to accommodate today's multimedia applications. Moreover, the automotive industry has high expectations for reliability and stringent requirements for reinforcement, which has led to a strong preference for storage systems that are highly resistant to shock, vibration, heat and humidity.
Compact package
In light of these trends, next-generation industrial-grade small-size solid-state drives (SSDs) offer designers of in-vehicle infotainment systems a very attractive storage option. These products are available in an integrated or discrete version. Integrated NAND modules such as the SST NANDrive product line combine an integrated ATA controller with one or more NAND flash dies in a single package. These devices offer full IDE flash drive functionality and compatibility in a compact 12mm x 18mm x 1.4mm BGA package. The designer simply has to install the BGA on the system board. At boot time, the system treats the device as a system drive via an ATA or IDE interface.
As a storage solution that is completely silicon-based and does not contain any mechanical moving parts, these drives offer designers a better opportunity to meet the automotive industry's stringent shock and vibration specifications. From a performance perspective, small-size SSDs not only eliminate the seek process that disk storage systems must perform (averaging 13ms), but also provide up to 30Mbps read and write performance. The current generation of NANVRive devices meets the industrial temperature range and offers up to 8GB of storage space for higher density in the future.
Smaller size
The two main advantages of small size SSDs are smaller size and higher performance. Over the past decade, automakers have introduced more and more electronic subsystems into their cars, so shrinking the size of electronic devices has become an increasingly high priority. For example, current conventional cars integrate 30 to 50 microcontroller-based systems. Although hard drive manufacturers continue to make progress in reducing product size, current drives still require much more space than alternatives. For example, the standard size 40GB hard drive is 70mm x 100mm x 9.5mm, while the industrial grade version of the NANDrive is 12mm x 24mm x 1.4mm. In terms of reduced weight, only NANDrive weighing 0.8g is less than one percent of the weight of the hard drive.
Improved data integrity
Data integrity and extended IC durability are the most critical storage subsystem considerations. Today's small size SSDs offer a variety of features that suit these requirements. For example, to compensate for random read errors that may occur when using NAND flash, the SSD provides an embedded error checking and correction (ECC) circuit designed to ensure the accuracy of the data as it enters and exits the memory. For example, NANDrive provides an 8-bit hardware ECC engine.
Bad-block management poses another challenge. Unlike NOR flash, the design of NAND ICs allows for several bad blocks. To manage these deficiencies, firmware-based bad block management functions are activated during small-scale SSD initialization, determining the location of these bad blocks and mapping them outside of the storage array. The firmware then directs the controller to prevent it from using these specified blocks. When additional bad blocks are found, the firmware updates the mapping to ensure that these blocks are not used.
MLC architecture
The durability of write operations constitutes another obstacle to the use of small size SSDs in the automotive market. Flash ICs suffer from limitations in the durability of write operations: after repeated erase and write cycles, the memory no longer retains data. The more complex the IC architecture, the smaller the memory cell size and the lower the durability of the IC.
For example, a single-level-cell (SLC) flash device is typically specified at 100,000 cycles. Devices that use more complex multi-level cell (MLC) architectures, such as those currently used in portable consumer devices, are typically specified for 10,000 cycles. Small-size SSD manufacturers have begun to use SLC flash in SSDs for the automotive market to mitigate this risk.
In addition, durability can be extended by using a wear leveling function in the firmware of the device. The wear leveling algorithm matches the age counter to the logical and physical sector maps on the flash media, thereby tracking memory usage by block or page. The age counter is incremented for each write and erase action. These complex algorithms direct the controller to transfer memory writes to smaller blocks, thereby automatically balancing memory usage. This technology takes advantage of all sectors of the flash memory, allowing them to reach write limits simultaneously, thereby maximizing SSD endurance.
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