Embedded Systems Design Europe - May 2008 - (Page 38)

memory faster read access. OneNAND requires 1-bit ECC for each 512-byte sector and requires NAND ﬂash management functions implemented either in the host chip set or in a separate standalone controller. On the other hand, OrNAND combines MirrorBit NOR with a NAND ﬂash interface, which offers faster write time than its predecessor NOR devices. OrNAND also requires 1-bit ECC implemented either in the host chip set or in a separate standalone controller to ensure reliable system boot-up. Moreover, the maximum density currently supported by OrNAND is only 1 Gbit, which is less than the maximum density of currently available NAND ﬂash. MANAGED NAND FOR DATA Due to the limitations of the embedded NAND controllers, many system designers are looking at managed NAND solutions. Several vendors have come up with managed NAND memory products that alleviate the complexities of a conventional memory subsystem in embedded applications. These managed NAND memory products, including iNAND, GBNAND, moviNAND, Managed NAND, and NANDrive, are used mainly for data storage. They reduce system complexity by effectively managing the built-in NAND ﬂash with a NAND controller and ﬂash ﬁle system (FFS) integrated into the same device as shown in Figure 2. These products use a standard interface such as Secure Digital (SD), MultiMediaCard (MMC), or Advanced Technology Attachment (ATA) for easier integration. For example, iNAND and GBNAND offer the SD interface, moviNAND and Managed NAND offer the MMC interface, and NANDrive offers the ATA interface. These products don’t offer XIP access and as a result, systems that use them may need a NOR ﬂash for the boot function. Using a managed NAND device eliminates the need for a complex NAND management function on the host. As a result, the chip-set vendors needn’t worry about keeping up with the evolving NAND technologies, thus enabling vendors to focus more on their core competencies. MANAGED NAND HYBRID BOOTS Because managed NAND ﬂash doesn’t provide boot capability, system designers still must use a higher cost NOR ﬂash device for boot-up. However, hybrid products, including mDOC H3, are now available. These hybrids use RAM and managed NAND in a one device, as depicted in Figure 3, to simplify the conventional memory subsystem. Hybrid products solve the boot issue associated with the managed NAND. They can boot directly from the NAND ﬂash, eliminating the need for a higher cost boot NOR ﬂash device, which may reduce the overall system cost. Managed NAND hybrids also help to reduce component count and save board space, which makes them suitable for spacesensitive applications like cell phones. These solutions are available in higher densities because they use NAND ﬂash for nonvolatile storage. On the down side, NAND hybrids have a longer boot time because they must copy the boot code from the 38 MAY 2008 | embedded systems design europe | www.embedded.com/europe NAND into the boot RAM after poweron. Also, NAND hybrids are complex, difﬁcult to integrate, and require an advanced operating system that supports demand paging on the host. mDOC H3 uses a NOR-type bus to interface with the host processor and offers faster read performance than NAND ﬂash and faster write performance than NOR. Due to the faster write performance, these devices are suited for storing multimedia. Using a managed NAND or even a managed NAND hybrid with boot capability doesn’t drastically reduce the memory subsystem’s overall complexity. The system designers must still manage the complexity associated with different memory types, interfaces, vendors, vendor-speciﬁc features, and so forth. These types of memory subsystems require many components, more pins, and complex hardware and software development, resulting in increased system cost, board space, development time, and power consumption. At the same time, they increase the complexity of the external memory controller in the http://www.embedded.com/europe

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Embedded Systems Design Europe - May 2008 Contents Microsoft Provides Embedded Roadmap Enea Buys Developers Irish Start-Up Raises Funds for Telecom FPGAs Kontron Promotes COM Express Nano Mentor Nucleus Platform Provides UI for Atmel Small Form Factor Boards Head for the SUMIT Proffibus Advances IO-Link Integration Embedded Developers Cautious on Multicore Auto Cooperation Improves Test Altera Launches DO-254 Partner Network Building an ‘Instant-Up’ Real-Time Operating Systems An Architecture for Reusable Embedded Systems Software Free up Bandwidth in PCI Express Evaluating Software in Medical Devices Circuit Sensitivity in Analog Circuits Choosing Flash Memory New Products Advertising Contacts

Embedded Systems Design Europe - May 2008

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