If you’re on LinkedIn, check out the Realtime Embedded Engineering Group for an interesting and often lively discussion of the issues facing our community. We particularly enjoyed reading the recent thread about the drivers included by hardware vendors being less than optimal for most flash parts. The consensus can be summed up in one blogger’s statement;

“What many silicon vendors refer to as a ‘driver’ is nothing more than the code left over by their inhouse hardware development team. This code typically exercises just a small subset of the device capabilities (or whatever they were working on last) and doesn’t even come close to meeting the definition (or spirit) of a general purpose device driver.”

We couldn’t have said it better ourselves. A lot of our time in developing our FlashFX family of flash memory drivers is spent ensuring completeness, reliability and portability to a wide variety of CPUs and operating systems.

It’s been over 20 years since NAND flash was supposed to take over the world, so why is the ‘ultra-portable’ laptop I’m writing this on still using HDD? And why, nearly 30 years after the invention of flash, are we still debating its applications vs. the rotating platter? Given the performance advantages of flash and the mechanical shortcomings of HDD – things like wear and susceptibility to shock and vibration, not to mention the latency associated with spinning up for reads – it’s no wonder that flash has long been the darling of memory technology futurists. So why after all this time has flash not replaced older technologies? I’ll give you a hint: It’s all about the money. But it’s not only about the money – check out our list of five top barriers to flash adoption:

1. Cost – Despite years of oversupply in the flash market, and the corresponding reductions in price, flash is still relatively expensive when compared to HDD, especially on a $/bit basis. To make matters worse, the current economic climate has taken its toll on the flash industry, spurring several rounds of consolidation and requiring flash vendors to curb manufacturing costs by shrinking portfolios and closing fabs. Predictably, these changes in the supply landscape are causing prices rise in many cases, making the cost factor an even bigger problem for flash.

2. Shrinking lithography = lower endurance – One way for flash manufacturers to remain competitive is to use smaller die size to reduce raw material costs. Just a couple years ago, the vast majority of NAND flash was manufactured with 90nm lithography. Most vendors are now planning to move to 30nm technology either this year or next. An unfortunate side-effect of smaller lithography is significantly decreased endurance. SLC NAND, which had 100K + erase cycles, is now predicted to be in the 50-70k range. The biggest impact is on MLC NAND where the endurance has gone from 10k erase cycles to around 3k (a 70% reduction!).

3. Increasing ECC – Another side-effect of shrinking lithography is an increase in error rates for flash, requiring stronger correction codes. Most SLC NAND flash today requires 1-bit correction. That number is predicted to increase to 4-bit on 30nm NOR parts. And the ECC outlook for MLC NAND is even worse, requiring ECCs greater than 12-bit (compared to 4-bit or 8-bit today). These increased ECC requirements mean the controller design for managing flash will become more complicated, and more difficult for OEMs to implement. Performance will also be impacted, especially if the ECC is done in software running on the host processor.

4. Vendor volatility – Churn or volatility in the flash market, the products of a difficult economic climate, are making it difficult for OEMs to find a reliable source of flash parts. Examples are everywhere; A major flash supplier is currently under Chapter 11. There are merger talks happening between SanDisk and Samsung. Asian vendors have been hit especially hard, particularly those also in the DRAM business. OEMs are rightfully concerned about interruptions to their production cycles in the midst of all this turmoil.

5. Lack of killer application – While NAND flash densities have continued to increase, the industry is still waiting for the killer application to gobble up these immense quantities of flash. For long SSDs have been viewed as that application but they have not taken off as fast as the flash industry would have liked.

In spite of the obstacles faced by the industry, flash remains a strong and growing choice for data storage and has put breakthrough devices like MP3 players and smart phones (iPhone!) into the hands of millions of consumers. Early adopters of SSD technology in laptop computers, netbooks and enterprise applications are making a solid case for mass market potential there, which should significantly drive flash adoption in the next few years. Visit the FlashFX Tera page to learn how Datalight is making flash easier and more competitive.

Sea Change Hits Consumer Electronics as Customers Demand Long-term Value

For the first time in more than a decade, people are saving again. In 2007 and years prior, the savings rate hovered around zero as we maxed our credit cards and lines of credit, driving the savings rate into the red and giving the world’s manufacturing base an almost unbelievable boom. In January 2009 though, something unexpected happened; the US savings rate suddenly moved above 5%, the highest in decades. As news of our cloudy economic picture has emerged, consumer behavior is shifting away from status-seeking luxury purchases toward more value-based buying patterns, forcing manufacturers around the world to take notice. And after decades of excess, the shift to thrift is looking like a lasting trend.

But what does this mean for Embedded? As consumers focus on needs over wants, they will increasingly seek out products that are proven durable and reliable.

This will have broad implications for manufacturers of everything from cars to clothing, refrigerators to embedded devices. Today’s consumers are choosing efficiency, durability and value over gee-whiz gadgetry. Consumer mobile OEMs too must focus on delivering value and fewer, more targeted features. Rather than packing devices full of a laundry list of apps and expensive hardware, this means streamlined offerings and more segmented products, while making sure the consumer doesn’t feel like they’re missing out. Motorola’s new EM330 is a prime example of this kind of pared-down, demographic-specific approach. The phone, called the MOTOROKR STAR is marketed specifically toward music lovers, offering a basic clamshell with music recognition software and download-on-the-go at a price point in the sub-$200 range.

As OEMs scramble to add value and enhance their reputations for durability and reliability, Datalight responds with products that support those goals. The combination of flexible flash management that lowers bill of material costs, wear-leveling algorithms extend flash life by several times, and the rock-solid reliability of our file system become essential components of a strategy to provide value to customers.

Many have remarked that markets are driven by a combination of fear and greed. Though the pendulum has recently taken a dramatic –and we believe temporary– move in the direction of fear, ultimately we know a move away from excess is good for all of us and good for the world we live in. Here’s hoping the trend toward value and quality is a long-lasting one.

5 Reasons for Ditching Managed NAND
Everyone knows that NAND has challenges: from factory bad blocks and spontaneous bit failures to endurance limits, etc. That’s why a few years ago managed NAND (NAND flash plus an integrated controller) seemed to be the answer, offering the density of raw NAND, while mitigating many of its inherent limitations. What many device manufacturers may not realize is that the management hardware comes with significant costs, both in terms of dollars per part as well as design limitations. In the world of tradeoffs in which every system designer lives, there are solid technical reasons to consider using raw NAND and leaving the management to software instead. While there are clear commercial advantages for Datalight (as a provider of vendor-neutral software-based flash management) to advocate this approach, we also believe that there are strong technical reasons that flash silicon vendors would do well to embed ECC capabilities into their NAND flash devices rather than relying on ‘total hardware’ solutions such as eMMC or other complex and costly controllers. Beyond the benefits outline below, this approach would allow the flash manufacturers the ability to continue to differentiate their products from others in the industry.

1.    Cost
The cost of managed NAND parts is coming down, but the stuff still sells at a premium over its raw NAND brethren. 

2.    Flash Optimization
There are many new features of NAND available to us today.  Performance features such as cached reads, multi-plane operations, concurrency, and others are becoming invaluable to keep performance at the ever-increasing demands of portable media. The Open NAND Flash Interface (ONFI) has defined a standard method to query the capabilities and characteristics of NAND flash which can be put to use by both software and hardware systems. A software media manager offers the flexibility to take advantage of the most current flash memory features and put them to use efficiently, or to avoid certain features that may be unproven or problematic. A software solution will allow a developer to take full advantage of the media’s characteristics and features unburdened by the indirection or inability for the hardware to expose them.

3.    Visibility/Flexibility
Software (in general) is easily inspected and validated. Features such as wear-leveling move data around the flash device to optimize its life expectancy. Without the ability to inspect source code, a managed NAND solution makes it difficult to validate wear-leveling operation and/or characterize its effect on performance and reliability.  Hardware implementations are often generalized to suit a majority of use cases, while a software solution is easily tailored to the specific use case during development.

4.    Performance
Speaking of use cases, there are many system features that are not available to hardware that may make a generalized hardware solution less advantageous to a specific use case.  For example, system idle time can be used to improve the media performance by scheduling background cache operations and compaction to occur then.  Coordination between the file system and flash media manager can further optimize operations by freeing space when it will no longer be needed and having the media manager code cache certain regions of the flash where meta data might be held. Migrating flash management features to hardware removes this ability to coordinate with other components of the software stack, such as file systems.

5.    Reliability
Lest you think we believe that everything is better left to software, consider error detection and correction (EDC). Error rates are increasing substantially as flash manufacturers push the limits of physics.  Errors can be introduced externally by heat or other radiation, during writes or reads of data, and even to data that was successfully written at a different time. Historically SLC NAND flash required only a single bit error detection and correction (a hamming code is usually sufficient), while MLC parts require minimally four bit EDC.  As the die sizes continue to shrink, error rates will continue to increase, even for SLC flash. 
Calculating the codes to detect and correct such errors is getting increasingly complex and solving such a solution in software for higher-bit EDCs (above 4-bit) is time consuming and often unacceptably slow.  Hardware ECC is a necessary requirement for systems with high EDC requirements and where performance is a concern.

Many of the processors on the market today are incorporating EDC in their NAND controllers. Choosing one of these processors (e.g. TI OMAP 35xx) in combination with raw NAND flash and software management can give you the high-performance EDC to handle next generation flash while maintaining the design flexibility that a software manager provides.

Flash manufacturers have much to gain by adding ECC code into their NAND flash parts.  They know better than anyone what kind of ECC is necessary for a specific part and by adding just that one piece of hardware to their offerings, rather than the jack of all trades, master of none approach of complete flash management, they will better serve the markets. 

In short, features should reside where they can be handled most efficiently; ECCs belong in hardware, other flash management functions belong in software.  While managed NAND certainly has its place and its appeal in the market, we believe the best combination of value, performance and flexibility lies in using a combination of raw NAND and hardware with built-in ECC capabilities.

The Challenge
Recently, LG Electronics, a well-known Korean-based manufacturer of consumer electronics, created a multimedia-enabled portable navigator for the North American market. The LN790 features a 4.3” LCD screen, Bluetooth hands-free functionality, and video-enabled playback. Ruggedness and fast access to data are important to consumers in this market, so the device was designed to boot directly from a NAND mass storage environment using Windows CE. Unfortunately, LG product engineers had a difficult time getting the device to boot fast enough using CE’s FAL/FMD flash drivers.  At just over two minutes, the startup time did not match LG’s reputation for high-performance consumer devices.

The Datalight Solution
As LG engineers went searching for solutions to the boot speed problem, they discovered that Datalight FlashFX® Pro uses a more efficient approach to managing bad blocks than CE’s standard FMD/FAL drivers, which can speed boot time significantly.  This difference is especially apparent when the device is using a large NAND disk, because boot time is somewhat proportional to the size of the flash.
Why is FlashFX Pro more efficient? Startup with FAL requires the driver to read more data as part of its mount sequence, a lengthy process particularly if the disk is large. In contrast, FlashFX Pro requires a much simpler check of the media to complete the initial mount.

The Customer Payoff
After implementation of FlashFX Pro, LG engineers were delighted to discover that the device’s boot time was cut by more than half. By using FlashFX Pro instead of the native Windows CE drivers, LG designers were able to achieve the performance their customers expect from a premium-quality personal navigator.  There was also an additional benefit they hadn’t counted on – FlashFX Pro support for over 200 flash parts means that the LN790 will be future-proof from flash parts going on allocation, unexpected price fluctuations, and end-of-life issues.

SanDisk recently announced that it is end-of-lifing several flash parts in the mDOC family and OEMs who were using these parts in their devices are now looking at viable alternatives.  In order to help these affected customers make informed decision, we have published a new whitepaper on options for migrating from Sandisk mDOC flash family.

The paper is available at http://www.datalight.com/mdocwhitepaper/

Contrary to popular belief, flash memory does not last forever. Every flash part in existence comes with a finite number of write and erase cycles before the data stored becomes corrupted and the flash part unusable. Most flash file systems on the market today include a basic type of wear leveling, but all wear leveling algorithms are not created equal. Chiefly, wear leveling strategies can be broken into two camps: Dynamic wear leveling monitors high and low-use areas of the flash, and after a certain set point, will swap out high-use erase blocks with low-use erase blocks. Large areas of a disk may be occupied by rarely-changing data, forcing frequent system writes/erases to occur on the remainder of the disk and increasing the wear on those areas. Static wear leveling deals with this by moving static data to higher-use areas of the flash, thereby balancing the load. The idea system would use both kinds of wear leveling. Check out some real-world examples by reading our whitepaper on the topic:

A Short Study on Wear‑Leveling

Over the past fifteen years, flash memory has been widely adopted in mainstream consumer grade products having short lifetimes, often measured in months. In recent years however, flash memory has begun to break into more industrial and commercial grade devices with lifetimes counted in years. There are many unique characteristics of flash memory that have fueled its growth across these varying market segments, such as its ability to retain data without continued power; this benefit, however, comes at a cost of a finite lifetime and endurance. The hardware architecture and software technologies that extend the life of a flash chip are often ill‑considered or, at times, given more worry than necessary. While the limited lifetime of flash memory may or may not be problematic for products that are expected to last ten or more years, flash management software can expand the breadth of available flash parts for your project.

This paper focuses on determining when the limitations of flash memory lifetime become significant and what can be done about them.

Flash Lifetime Metrics

Flash memory lifetimes are described in two primary metrics which are generally touted on the first page of any flash memory manufacturers’ data sheets:

• Data retention
• Endurance cycles

Data retention is often listed at 20 years at a given operating temperature. Increased temperature ranges reduce the data retention period which further decrease as the flash memory is used at or near its specified operating temperatures. It is important to note that data retention is measured from the time data is successfully programmed.

The second metric, endurance cycles, is a measure of the number of write and erase cycles that the flash memory can endure before becoming unreliable. Flash memories are organized into a number of erase blocks or sectors and each must be erased prior to writing data. A typical erase block is 128KB in size, however may range from 512B to 2,048KB or even more. Any given address within an erase block cannot be rewritten without an intervening erase. Erase cycles are cumulative and affect only those erase blocks being cycled. In other words, an error in any erase block is constrained to the data of that block.

Erase cycles range from 1,000 to 1,000,000. While these ranges have an order of magnitude difference, it is the application the flash is placed into that will primarily define the product lifetime.

What is Wear-Leveling?

Wear‑leveling is a process to ensure that an entire flash memory device or an array of devices is used in a uniform fashion in order to extend the overall lifetime of the flash.

For a simplistic example of wear-leveling, let’s look at a data recorder device with the following characteristics:

• Application: The device collects and stores the past 24 hours of field data by simply writing and rewriting the data to the same location on the flash.
• File size of data to be recorded: 128KB
• Erase block size (of the flash): 128KB
• Flash memory endurance: 1,000 cycles

With one spare area, the device is assumed one cycle per day each year:

(1,000 cycles ÷ 365 days) * 1 spare area = 2.74 years

In this example, it would take about 2.74 years to cycle that one erase sector 1,000 times.

For the data recorder device to accommodate the write‑erase rules of flash memory, it would have to complete an erase operation to start writing the next day’s set of data. To make the data recorder more robust – to ensure that it doesn’t lose a whole day’s worth of data – we can set aside a second erase block, and erase the first block only after the second set of data was recorded. The resulting side effect is the introduction of a simple wear-leveling scheme.

With two spare areas, the device is assumed one cycle every two days each year:

(1,000 cycles ÷ 365 days) * 2 spare areas = 5.48 years

With these parameters, the period of time prior to cycling the flash to its lifetime has just been increased to almost 5.5 years!

This simple example shows how distributing a fixed set of writes across more flash sectors can increase the period of time prior to cycling the flash to its specified limits. The following sections describe how to account for the important variables associated with wear-leveling techniques, and determine the expected lifetime of the flash in any application.

Continue: A Short Study on Wear-Leveling

Consumer electronics and embedded software devices are using larger amounts of flash memory for nonvolatile storage than ever before. So what kind of flash memory should you use? The choice between using NAND and NOR Flash may not be a simple one for the complex embedded devices being developed today. While ever-larger media files are driving increased demand for inexpensive NAND, powerful new operating systems and intricate applications running on fast processors ask for the fast-executing code NOR can support.

Read Datalight whitepaper Choosing NAND or NOR Flash Memory: Tradeoffs and Strategies to Learn More

Consumer electronics and embedded software devices are using larger amounts of flash memory for nonvolatile storage than ever before. One important decision in designing such devices is what kind of flash memory to use: NAND or NOR?

NOR flash memory has traditionally been used to store relatively small amounts of executable code for embedded computing devices such as PDAs and cell phones. NOR is well suited to use for code storage because of its reliability, fast read operations, and random access capabilities. Because code can be directly executed in place, NOR is ideal for storing firmware, boot code, operating systems, and other data that changes infrequently.

NAND flash memory has become the preferred format for storing larger quantities of data on devices such as USB Flash drives, digital cameras and MP3 players. Higher density, lower cost, and faster write and erase times, and a longer re-write life expectancy make NAND especially well suited for consumer media applications in which large files of sequential data need to be loaded into memory quickly and replaced with new files repeatedly.

The choice between using NAND and NOR Flash may not be a simple one for the complex embedded devices being developed today. While ever-larger media files are driving increased demand for inexpensive NAND, powerful new operating systems and intricate applications running on fast processors call for the kind of fast-executing code NOR can support. An important example is a smart phone or PDA that combines a tremendous need for storage with a demanding set of application performance requirements. In some cases an optimal design might call for both types of flash memory in the same device.

Whichever type of flash is used in a device, there are certain negative performance characteristics that need to be mitigated. NOR is fast to read current data but markedly slower to erase it and write new data. NAND is fast to erase and write, but slow to read non-sequential data through its serial interface. NAND is also prone to single-bit errors, requiring rigorous algorithms for error detection and correction.

Well-designed software strategies can be very effective in increasing the performance and reliability of Flash hardware. The goals of flash memory management software include:

Avoid loss of data. Perhaps the most important goal in managing flash memory is to assure that no data is ever lost as a result of an interrupted operation or the failure of a memory block.  There are several ways that flash management software can achieve this goal. Rewrite operations, for example, can be managed in such a way that new data is written and verified before the old data is deleted, so that no power loss or other interruption can result in the loss of both old and new data. Bad block management is another important safeguard to prevent data being written to memory blocks that have failed. Software can check for bad blocks shipped from the factory, as is typical with NAND, and avoid writing to those blocks from the beginning. When blocks go bad over time they can be identified and managed so that they are no longer used. Finally, as the end of media life nears, good memory management software can implement a graceful strategy such as placing the entire flash unit in a read-only state, thereby avoiding data loss when the number of block errors exceeds a predefined number.

Improve effective performance. Two ways media management software can improve performance are background compaction and multithreading. Compaction reclaims space by identifying blocks that have obsolete data that can be erased, copying any valid data to a new location, then erasing the blocks to make them available for reuse. Such compaction increases the amount of usable space on the media and improves write performance. Compaction may also help to defragment noncontiguous data for improved performance on read operations. The space recovery is particularly valuable for the more costly NOR memory and the defragmentation benefits the slower-reading NAND. Compaction is best performed in the background during idle time, however, or it can interfere with critical operations and degrade performance. This is where a multithreading system becomes important. By allowing high-priority read requests to interrupt low-priority maintenance operations, a multithreading system can reduce read latency by orders of magnitude compared to a single-thread solution.

Maximize media lifespan. When some blocks of memory contain fixed content, such as binary code, the remaining blocks will experience increased demand for erase and write operations, leading to earlier failure. Wear-leveling algorithms can prevent overuse of memory blocks and prevent a “stalemate” scenario in which a small region of memory becomes locked in a pattern of repeated writing and compaction. Wear leveling software can monitor block usage to identify high-use areas and low-use areas containing static data, then swap the static data into the high use areas. It can also balance write operations across all available blocks by choosing the optimal location for each write operation.

The decision between NAND and NOR memory will ultimately depend on both technical and pricing requirements of the device being built. Whatever type or combination of flash is used, it is prudent to include memory management software to prevent data loss while improving the performance and maximizing the lifespan of the memory.

Interesting piece of news today – Digitimes is reporting that Samsung has informed its customers that it will be reducing supply of NAND Flash chips because of the huge order placed by Apple. This story is being picked up by several news outlet including Engadget. While this is good news for Apple and all those vying for the 3G iPhone, it underscores the challenges other OEMs that depended on Samsung Flash will be facing. NAND flash market is very volatile with demand – supply economics changing rapidly. Intricacies of flash memory force most OEMs to rely on a single vendor for supply, that way they do not have to implement support for several flash parts in their design. While this may seem the easier route, situations such as today’s causes production to come to halt or a significant redesign, both which are very expensive alternatives.

One of the ways to reduce such risk is to include support for multiple flash parts and use multi-sourcing to source flash parts from 3-4 flash vendors. If you are using an intelligent flash manager like FlashFX Pro , you are already covered since FlashFX pro supports 200+ flash parts from all top flash vendors. For others, it can still be done with some serious effort during planning and design time. Consider this work as an insurance against an event such as today’s.