原创 multimedia handsets with the right memory architec

Feature phone needs
Feature phones constitute the majority of the mobile handset market. They''''re standard phones enhanced with features to provide entertainment. The killer application of feature phones in 2004 was the camera, which enable users to not only take pictures and video clips, but ostensibly to send them as MMS messages to other users (incompatible network standards don''''t fully support this extended capability).

To support this enhanced feature set, feature phones have undergone architectural changes. Today, two architectures dominate this category, enhanced and multimedia-centric (see the figure). The enhanced legacy architecture offers only a slight improvement over basic voice-centric designs. It introduces additional flash media for storage and strengthens the baseband from an ARM7 to an ARM9. This architecture can support basic camera functions and simple Java games, but can''''t support advanced video capabilities and 3D gaming.

Two common feature-phone architectures are the enhanced legacy (top) and the multimedia-centric (bottom).

A dedicated multimedia coprocessor was introduced in the multimedia-centric architecture. The baseband continues to use a relatively weak ARM processor (usually ARM7), and is responsible for all traditional handset functions and the OS execution. The multimedia coprocessor, in contrast, is based on an ARM9 and higher, and includes additional multimedia-targeted state machines. This processor handles all multimedia and graphic-intensive applications, and is used on demand of the baseband. This architecture typically includes two memory subsystems, one for the baseband, to store and execute the OS, communications stack and applications; and one for the multimedia coprocessor, to store its code and all files managed by the file system (mostly multimedia). Although different, these two architectures both require flash media to store pictures, video clips, and games downloaded by the user, but capacity requirements differ depending on the phone segment.

Low- to mid-range feature phones
Low- to mid-range feature phones provide a basic, low-res camera (VGA or lower) and gaming. A low-res still picture only occupies 40 kbytes or less, a requirement that NOR can meet. Many feature phones provide 32 Mbytes of NOR, the upper limit of NOR as a competitive media, and in many cases an additional slot for a NAND-based removable card (mostly SD or MMC form factor).

For these devices, NAND media offers a marginal cost improvement, which many vendors don''''t find compelling enough to warrant an architecture change. As photo resolutions increase, a growing demand for built-in NAND media is evident. NAND will first serve as a disk-like solution only, because paging software isn''''t yet available in the real-time OSs used in these handsets, resulting in increased PSRAM size and reducing the NAND/MLC NAND cost advantage. However, to further reduce the BOM while increasing the storage capacity, memory vendors are joining forces with feature-phone OS vendors to introduce OS paging capabilities. Once ready, this capability should dramatically accelerate the penetration of bootable NAND into handsets as the only NVM media on board, serving both as a code and storage media. It''''s important to remember that most chip sets for feature phones and most OSs don''''t support raw NAND, and thus designers turn to EFDs for NAND support.

Mid to high-end feature phones
At the upper end, the feature phones offer a VGA or higher-resolution camera (the mainstream camera for these devices in 2005 is 2 Mpixels), and are capable of video recording, some image processing and advanced gaming. These devices are based either on the multimedia coprocessor architecture, or on a higher performance baseband processor (ARM11) that''''s robust enough to manage multimedia. In such handsets, NOR media is not a viable solution, as evidenced by the fact that there''''s massive penetration of NAND flash technology. The most basic function of NAND in these devices is that of a disk drive, much like the hard drive in a PC. However, many handset vendors are taking advantage of EFDs to eliminate the additional NOR device to store the multimedia processor code.

About the author
Arie Tal is the director of marketing for M-Systems’ Mobile Division. He received an MBA from Haifa University and a BA in economics from The Technion, Israel Institute of Technology. He also has a practical engineering degree in Electronics from Netanya College. Tal can be reached at .