System information

9 Benchmarks and Verification
protocol of the VNC framebuffer is the RFB
1
protocol. It supports color depths of 8,16 and
32 bits. However, the VNC client normally chooses the highest color depth of 32 bits per
pixel. Figure 9.6 depicts the frame rate provided by the VNC server in relation to the VGA
mode. In this case, the frame rate is the maximum number of frames per time which can be
generated by the VNC server. The frame rate is measured for two cases: a full framebuffer
generation and a given framebuffer in which 15% of the content has to be changed. As a
result, the VNC server spends approximately one second to generate and provide the whole
framebuffer content. Thereby, the VNC server has to process following steps:
• Copying the video data from the video plane to the framebuffer.
• Conversion of the indexed color
2
based VGA pixels into true-color
3
pixels.
• Sending of the pixel data to the VNC client.
As a matter of fact, the video data of the screen mostly changes in parts and the corre-
sponding VNC framebuffer does not have to be regenerated completely. The reduction of
the video data which has to be converted into a VNC framebuffer increases the frame rate
of the VNC server. The bars filled with a pattern shown in figure 9.6 depict the achieved
frame rate of the VNC server, if only 15% of the associated VGA data were changed. Except
for the video modes 0x10-0x12, the VNC server achieves frame rates of up to 10 frames per
second. These frame frequencies are sufficient to control the computer by remote. As ex-
pected, the frame rates decrease with the screen resolution, but the color depth do not have
a relevant impact on the frame rate. The reason for this is that the VNC server normally
uses a fixed color depth of 32 bits for the framebuffer independently of the running video
mode. In this process, the original color depth of the video mode is expanded to 32 bits.
9.2 USB CD-ROM Performance
The CHARM card emulates a USB CD-ROM or flash device. Basically, the CHARM USB
device is used to provide an install media to the host computer. The read performance
is an important characteristic of this USB device. The throughput can depend on several
parameters: block size and packet size.
Packet Size is the size of the logical buffer which is used by a USB device for sending
or receiving a single packet. The Transfer Buffer of the USB controller contains a
plurality of this packets. A pointer defines the start of the actual sending or receiving
packet. The USB defines the allowable maximum bulk data payload sizes to be only
8, 16, 32 or 64 bytes for full-speed endpoints (USB 1.1) and 512 bytes for high-
speed endpoints (USB 2.0) [104]. But the used USB controller only supports low
or full-speed endpoints. However, the USB controller can deal with packet size of
1
Remote Framebuffer [24].
2
The pixel does not contain the full information to represent its color, but only its index into a color
palette.
3
Truecolor is a method of representing the image information in an RGB color space.
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