A new addition to the Philips“intelligent drive”features,
Seamless Link acts to manage and minimise
the effects of buffer under run (BUR), a common cause
of wasted discs during the CD writing process.
INTRODUCTION
Today, burning discs with a CD writer has become a common method of storing and
distributing data, text, video and audio files for PC users. With advances in writer speeds
and performance, greater ease of use, improved writing application software with
“drag-and-drop” functionality, and simple Graphical User Interfaces (GUI),
users today require less time and hassle when burning their first disc.
Other advances in CD writing are related to write integrity, and ensuring optimal writing
on nearly all media, as example, with Philips Thermo Balanced Writing (TBW) and Self
Learning strategies.
However, even with exponential strides in ease of use, and a mainstream place in new PC
systems for CD writers, users, especially those with older systems, still face an occasional
buffer under run error message. A less frequent error for users of new PC systems,
BUR is still an annoying problem.
™
While first addressing the problem via a software solution (“Ultra-Buffer ” in co-operation
with AHEAD), Philips now takes the solution a step further, by placing the solution
“on board” the CD writer. For both users of new and older systems, Philips Seamless Link
“on board” offers an excellent management solution for BUR without tying users to a
specific application software provider.
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ABOUT BUFFER UNDER RUN (BUR)
Buffer under run can occur when the users’ PC or a host PC cannot supply a steady and uninterrupted flow
of data from the data source, typically a CD ROM or HDD, to the internal DRAM buffer of the CD writer
(writer buffer) (Fig. 1). If this transfer of data to the drive writer buffer is interrupted, then the buffer is not
kept full (Fig. 2). If the interuption is long enough, the "writer buffer" gets empty, the writing process stops
and the disc is ruined (Fig. 3). Buffer under run occurs most frequently when users are writing to a CD-R or
CD-RW disc in either Track-at-Once (TAO) or Disc-at-Once (DAO) mode.
The causes of BUR have been numerous and are related to the PC system, the system configuration or set up,
and the CD writer itself. Most sources of BUR have been reduced in newer PC systems (with faster CPUs
and HDDs with transparent Thermal Recalibration), and by improvements in both
CD writer and the application software.
Fig. 1, Typical CD writing process: The data that needs to be written on the disc is transferred from the
source over the system bus, and is put into the DRAM buffer of the CD writer. From this buffer, the data
is put onto a disc in the writing process.
CD writer
Internal DRAM buffer,“writer buffer”
compensates for short interruptions
in the data stream
Fig. 2, Typical CD writing process: Short interruptions in the transfer of the data over the IDE bus will cause
the writer buffer level to drop.
CD writer
If the data stream is interrupted, the speed at which
the data is sent to the writer is lower than the speed
at which the data is written to the CD
=> the level of the writer buffer
will drop.
After the interruption, the writer
buffer level will rise again
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Fig. 3, Typical CD writing process: Buffer under run occurs and results in writing failure, disc is ruined.
CD writer
Writer buffer level drops to 0%
· No more data available to write to the CD
·Writing stops => BUR
BUR occurs when this
stream is interrupted
Several primary sources of BUR are:
·
·
·
·
·
·
·
Insufficient PC processing power (low speed CPU, DRAM size, no DMA support)
System configuration not optimal (DMA switched off)
Too much user interaction during CD writing (launching or running additional applications)
Insufficient performance of the source drive (CD ROM or HDD in user system or network)
Insufficient performance from the mastering software, espec. at higher recording speeds
Insufficient performance of the writer (not enough internal memory or buffer…)
Scratched or dirty media (source drive needs multiple retries to successfully read)
BUR MANAGEMENT FROM PHILIPS!
Seamless Link, the Philips solution, is a BUR management solution that is “on board” the drive and prevents
a lost disc when a buffer under run occurs during TAO or DAO writing. Detecting the clues of a imminent
BUR ahead of time, Seamless Link pauses the writing in a controlled way, and restarts the writing when the
danger of the BUR is gone. The result is effective with most older systems, when proper system set-up is done,
and Seamless Link works transparently with most writing application software.
The primary benefits to users of both new and older PC systems are:
·
·
The Philips "intelligent drive" pro actively manages the consequences of a BUR during CD writing
The solution allows users greater ability to launch and run other applications..., or surf the web,
while burning a CD.
Although Seamless Link is an excellent tool for managing the impact of BUR when it occurs, Seamless Link
does not improve writing quality.
For improvements in writng quality, refer to the Philips' Thermo-Balanced Writing (TBW) white paper.
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HOW SEAMLESS LINKWORKS
The Seamless Link algorithm (Fig. 4), constantly monitors the writer buffer level. If the writer buffer level
drops below a threshold value, the algorithm concludes that a BUR is imminent and stops the writing process
in a controlled way. This means that the data stream from the buffer to the disc is halted, and allows the
buffer to be filled up again.
The exact location where the writing stopped is stored in the drive’s internal memory. In the meantime,
the buffer level is continuously monitored and as soon as the buffer is full again, the algorithm will let the
drive seek to the location where the writing stopped. It then resumes the writing process as soon as the laser
is on the exact spot where the writing stopped. This type of writing eliminates the gap, which occurs between
two individual writing operations during traditional writing. Hence the name Seamless Link.
Fig. 4, The Seamless Link algorithm:
SUMMARY
Seamless Link offers excellent management of BUR incidents when writing CD discs in Track-at-Once (TAO)
or Disc-at-Once (DAO) mode. By utilising the Seamless Link algorithm to monitor the CD writer buffer,
chances of a ruined or wasted disc are made remote.
In addition, Seamless Link gives end users greater confidence in running other applications during the CD
writing process, AND freedom from the time and frustration of retries due to a buffer under run incident.
© Philips Optical Storage N.V. 2001
All rights are reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner.
The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed
without notice. No liability will be accepted by the publisher for any consequence of its use.Publication thereof does not convey nor imply any license
under patent- or other industrial or intellectual property rights.
Date of release: July 2001
Document order number: 3104 145 50609
Printed in The Netherlands
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