The latest cell phones and PDAs are very video-centric. When not being used as communication or information appliances, they provide entertainment. Previously, most chip sets designed for use in cell phones or PDAs included a basic 2D graphics processor that handled simple bit-mapped graphics and character-oriented monochrome displays. All of the graphics operations were handled via software to minimize the amount of logic, and thus power consumption.
Such graphics engines were fine for character-oriented operations, but today's cell phones and PDAs do much more. Color displays with up to quarter-VGA-class resolution will be common in the next year or so. Dealing with images that contain 50,000 or more pixels will require hardware to provide the responsiveness needed to display video or play games infused with lots of screen action.
To attain this level of graphics performance, a new generation of graphics coprocessor or complete multimedia applications processor is needed. The graphics coprocessor can be added to existing designs without a major redesign of the main processor subsystem. Such chips might typically include a high-performance 2D graphics engine with features such as bit-block transfers, line drawing, Sprite handling, font caching, scaling, and other compute-intensive operations. Also included on these chips would be a video accelerator that performs MPEG and JPEG decoding.
However, such an approach would still consume a significant percentage of host CPU cycles. This could cut into overall system performance because CPU cycles might not be available for other tasks. Of course, using a faster CPU could compensate, but that might have a negative impact on system power consumption. So, designers must make a tradeoff between performance and power.
Another approach puts more horsepower into the solution by adding an ARM9 RISC processor to the graphics and media support engines. At the same time, the design must be completed with a strict power budget to ensure that the resulting chip doesn't become a power hog in the overall system. Using this architectural approach, system designers can replace the highly integrated system-control chip with one that also packs significant graphics acceleration.
ARMING THE GRAPHICS SUPPORT
Designers who want to maintain their current CPU and software architecture can leverage graphics support chips from ATI Technologies, MediaQ, and Seiko-Epson. Such companion processors are fine when systems have the space to add an extra chip to handle the graphics and media support. But for applications when chip count is paramount, designers at MediaQ and NeoMagic (www.neomagic.com) crafted ARM-based solutions that deliver feature-rich system solutions that tightly integrate the processor and graphics.
A trio of MediaQ chips gives designers a choice of features based around an ARM 922T RISC processor. The MQ9000 includes 2D graphics acceleration, a Java acceleration engine, a CMOS/CCD digital camera interface, 320 kbytes of embedded static RAM, some video post-processing circuits, and the LCD panel controller. Other system resources include a keypad controller; a USB 1.1 client port; several UARTs capable of handling IrDA, Bluetooth, and 802.11 interfaces; an AC97/I2S audio interface; and a serial-peripheral interface (SPI). A 4-bit SD-memory card interface allows data to be rapidly transferred to or from the on-chip memory.
The chip supports LCD panels with up to 320- by 480-pixel resolution and 16-bit/pixel color depth. The back-end video processing supports MPEG-4 steaming video. With built-in timing control, the chip interfaces directly to many LCD panels.
Two additional versions, the MQ9100 and 9150, offer a superset of features. Both increase the amount of on-chip SRAM to 480 kbytes and add a full JPEG encoder and video processor. Each also supports two LCD panels—a main display panel and a secondary panel. With these extra features, the MQ9150 can handle higher-resolution, 1.3-Mpixel image sensors to capture XGA-class images (Fig. 1).
Along with graphics and media acceleration, the on-chip Java accelerator enhances applications written in Java. That lets the Java applets run faster and implement more complex tasks.
Based on an ARM926EJ-S RISC processor, NeoMagic's MiMagic 6 multimedia applications processor also speeds up Java-based applications. Yet the chip is the first to incorporate a 3D graphics engine for handheld applications. The engine can provide images at up to 1 million triangles/s. For 3D graphics, NeoMagic developed an associative processing array. It incorporates a massively parallel architecture that delivers over 1 billion operations per second. Thus, the chip will perform new, complex imaging algorithms and offer more functionality (Fig. 2).
Also included on-chip is a high-quality MPEG-4/H.263-compatible encoder/decoder with full-function video camera features at QCIF 15/30 frames/s and CIF rates of up to 15 frames/s. Built-in signal processing provides auto white balance and edge enhancement of the video signals. To better handle multimedia applications, designers incorporated 1.7 Mbits of display SRAM. The internal LCD controller can handle STN and TFT panels with resolutions of up to 800 by 600 pixels with either 8- or 16-bit/pixel color depths.
The ARM RISC engine runs at up to 200 MHz and includes instruction and data caches of 16 kbytes each. The accompanying Java accelerator boosts Java applet performance by as much as eight times as opposed to executing the applet on the ARM core.
Additional system support functions include an audio subsystem with ACLink, MIDI, and microphone interfaces; two SD-memory card interfaces; a USB 1.1 (including transceivers) client; a quartet of DMA-backed high-speed serial UARTs (up to 920 kbits/s each); two SPI ports; and IrDA support. There are also some general-purpose I/O lines, several timers, dual time-base inputs, and a choice of baseband interfaces, as well as a 16-bit shared memory interface with a mailbox semiphore communications scheme, or high-speed UARTs with flow control.
With graphics engines like these powering the next generation of handheld appliances, expect to be better informed and entertained than ever before.