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Posted - 11 May 2004 :  10:06:04  Show Profile  Email Poster
Q. What factors should I consider when choosing a graphics controller from Eurotech?

Eurotech offers display controllers to meet a range of embedded design requirements. This article describes some measures of graphics performance that may help to select a Eurotech product to meet your application's demands.

Frame Buffer Memory
The frame buffer is the block of memory which the display controller maps to a display.

The amount of frame buffer memory needed for a display is directly proportional to the size and color depth of the display. For example, a VGA (640x480) display at 8bpp requires 300 kiB of frame buffer memory, while an XGA (1024x768) display at 16 bpp requires 1536 kiB.

The location of frame buffer memory on or off the system bus impacts display and application performance. Display controllers with their own frame buffer memory do not need the system bus to refresh the display. This frees the bus for more efficient application operation. More importantly, separate frame buffers allow use of larger panels without the risk of occasional display interruptions (e.g. from other bus users, such as PCMCIA). You can read more about bus bandwitdth and display performance at forum topic 580.

Finally, some controllers can make use of larger frame buffers for quickly switching between screens, supporting multiple displays or quickly merging graphics from different sources.

Display controllers that have separate frame buffer memory include:
  • Silicon Motion SM501

  • Epson S1D13806

  • MediaQ MQ200

Blit Speed

The "blit" (or "bit blit") process copies a digital graphic from application memory to frame buffer memory. The time it takes to perform a blit depends on the width of the system bus, the memory bus speed, and the engine that performs the memory transfer.

Here is a relative comparison of blit speeds:
  • Intel XScale PXA255 (100 MHz system bus; fastest)

  • Intel StrongARM SA-1110

  • Silicon Motion SM501

  • Epson S1D13806 (16-bit data bus; half the speed of the SM501)

Graphics Acceleration

Some graphics controllers can use graphics primitives. These primitives significantly improve display performance by offloading the CPU from mundane tasks such as line drawing and block fill. The extent of the acceleration features can vary from simple fill commands to panning, stretch/shrink with interpolation, alpha blending, surface texturing, color conversion or video decompression.

Libraries like Microsoft Windows' DirectDraw allow graphics applications to take advantage of available acceleration features across platforms; these libraries often bypass the graphical APIs for higher performance.

Graphics acceleration makes a significant performance improvement in applications that draw text and graphics to the screen, such as rapidly changing instrumentation displays.

Eurotech display controllers with graphics accleration include the following:
  • Silicon Motion SM501

  • MediaQ MQ200

Hardware Mouse Cursor

If your application will include a mouse, you may consider selecting a graphics controller that supports a hardware mouse cursor. Overall system performance can be noticeably impacted when the operating system must redraw the mouse cursor in software.
Hardware mouse cursor:
  • Silicon Motion SM501

  • Epson S1D13806

Multiple Displays or Display Types

All graphics controllers on Eurotech products support LCD displays. However, some applications require connection to analog VGA, CRT, video or television (NTSC/PAL) displays. Others may have a requirement to bring in analog video data. The Eurotech product line includes display controllers that can support these formats.

Analog VGA display output:
  • Silicon Motion SM501

  • Epson S1D13806
NTSC/PAL output:
  • Epson S1D13806
NTSC/PAL input:
  • Silicon Motion SM501 (requires Zoomed Video port adapter)

For further reading about displays on Eurotech products, see the Display topic index.
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