Multimedia processors for portable media players

Multimedia processors for portable media players

Integration and processing power are key to meeting today’s market demands

BY MARK MILLS
Freescale Semiconductor
Tempe, AZ
http://www.freescale.com

Over the last few years, the market for MP3 players and portable media players (PMPs) has undergone dramatic growth, accompanied by an ever-increasing list of features that typical devices support. The research firm iSuppli estimates that shipments will reach more than 250 million units by 2011. Features such as large LCD displays, video, and very rich user interfaces are becoming mainstream, and are essentially characterizing PMP devices.

It is worth noting that while general market growth is slowing, the PMP share is projected to increase significantly, with the non-PMP portion declining over time. Another key aspect is that storage is increasingly based on NAND flash even for high-end devices. Hard-disk-drive devices are confined to the very top of the market, mostly in products with low volume. This has been made possible by increasing capacity and reducing cost for NAND flash, along with power consumption and reliability advantages.

The net result is that NAND flash PMPs will be a very interesting segment to pursue for OEMs and semiconductor vendors in the next few years.

The first generations of MP3 players were basic, with simple user interface capabilities. Succeeding generations support more sophisticated features such as video playback in addition to audio, and have very sophisticated user interfaces.

Despite the increases in storage and features, the cost of these players has been declining. Declining prices for players are forcing a significant reduction in semiconductor average selling price (ASP), while at the same time features must be maintained or even improved. Furthermore, existing features are expected to cost less for newer devices.

The main consequence for semiconductor companies providing system on a chip (SoC) solutions in this market is that high integration has been the key to success, because it allows for an incremental feature increase along with a decreased total system cost. Integration entails pulling features traditionally provided by several chips — the application processor, NAND controller, DAC and ADC — into a single SoC, as well as reducing the number of discrete and passive components necessary for the board design. This approach also helps reduce power consumption, because the control firmware has a much tighter control over all the involved elements.

Flexible solutions that can support as many NAND devices as possible are paramount. The increased versatility improves the operating efficiency of player manufacturers, given that storage cost is the dominant BOM factor. Certain NAND devices are subject to market shortages and may be hard to source during periods of peak demand.

Use case: Multimedia processing and display

Figure 1 shows how video data might flow through product system buses during video decode and display using an example system based on an ARM926EJ-S CPU running at 360 MHz.

Fig. 1. How video data might flow through product system buses during video decode and display using an example system based on an ARM926EJ-S CPU running at 360 MHz.

Examining Fig. 1, we can see the following:

• Compressed video data is read as a bitstream from external storage. The video stream is demultiplexeded via the CPU and compressed video frames are stored/buffered in system memory. Video frame data is stored and processed in the YUV color-space format where:o Y represents luminance (weighted sum of red, green and blue)o U and V are subtractive components representing blue and red colorso Because the human visual system is more sensitive to the luminance, it is possible to store a lower ratio of U and V components for every Y componento The YUV 4:2:0 format, for example, is used in compressed video storage. In this format, a 2 x 2 block of pixels has four Y samples and a single UV sample. This represents a 50% storage efficiency advantage over RGB• The software video-decoder executing on the CPU builds decoded frames via a mix of compressed frames and “reference” frames (YUV Ref)• Assuming RGB output, the hardware color space converter (CSC)/scaler/rotator is run on the decoded frames (YUV Display)

• At this point, there may be blending or other pixel processing steps performed by the CPU, after which processed frames are fetched via the display controller

We see that the above steps require not only high levels of CPU processing power, but also sufficient bandwidth from both system and external memory buses. Designing system buses and components for a video application can easily lead to feature and gate-count “bloat,” resulting in a part that is unattractive from a cost and power perspective. Attaining the correct level of performance requires detailed system modeling of the processor, system buses, hardware acceleration and memory controllers.

For manufacturers who want to build low-cost QVGA or wide-screen QVGA video players in applications such as portable media players and portable navigation devices, a single chip digital media system is optimal. It should have low power consumption with an integrated power management unit; one that includes a high-efficiency, on-chip dc/dc converter with 4.2-V output. Choosing a device with a power management unit that also includes an intelligent battery charger for Li-ion cells and is designed to support adjustable voltage control (AVC), can help reduce system power consumption. Having dc/dc converters and a clock generator that can be reprogrammed on the fly to trade off power versus performance dynamically will help minimize overall power consumption and extend the battery life of the system.

To provide the maximum application flexibility, consider a single chip device that integrates a wide range of I/O ports with the ability to interface to nearly any type of flash memory, ATA drive, serial bus or LCD. Another option to consider is the capacity for advanced connectivity applications, such as Bluetooth and Wi-Fi, through its integrated 4-bit SDIO controller and high-speed (3.25-Mbit/s) UARTs.

Analog is an essential component of every PMP. A device that integrates the comprehensive suite of analog components needed for a portable media players should include a high-resolution audio codec with headphone amplifier, 16-channel 12-bit ADC, 10-bit video DAC, mono speaker amplifier, high-current battery charger, linear regulators for 5-V operation, high-speed USB OTG PHY, and various system monitoring and infrastructure systems.

Look for a processor with at least 32 Kbytes of on-chip SRAM and an integrated memory management unit to provide the processing power needed to support advanced features such as audio cross-fading, as well as still and video decoding.

Designers and manufacturers in this new PMP landscape will find that high levels of integration and multimedia processing power can help them develop sophisticated products with fast time to market. With the right chipset, designers are free to focus on the unique look and feel that will differentiate their products in a very competitive marketplace. ■