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Customer perception of performance in IEEE 1394 Applications
Contents
* * * * * * Introduction Description Optimisation of OXFW911 Graphs of OXFW911 performance Optimal Performance Conclusion
Application Note OXAN 1
Oxford Semiconductor has designed the OXFW911 IEEE 1394 to IDE bridge with improved performance in mind. They have integrated the 16-bit flash memory onto the device to minimise the wait states incurred in accessing the flash. They have also optimised the interaction of the ARM7-TDMI based hardware and the firmware to reduce the relative time spent on the SBP-2 protocol conversion.
Introduction
This application note details the parameters important for customer perception of performance in IEEE 1394 applications. Much attention is given to the maximum performance of any given system. However, in the majority of applications small data block sizes are used and maximum performance will not be achieved.
Graphs of OXFW911 Performance
Figure 1 details the performance of the OXFW911 with various block sizes versus the same drive placed on the internal IDE bus. So far these figures for the OXFW911 have been limited by the speed of the drive used for testing, and the bus. These figures will be updated once faster drives are available. The tests were carried out on a NEC DTLA-307020 20.5GB hard disk using 15-11-2000 firmware. The tests were carried out on a Windows 2000 system using YAPT. The Host was a Dell PIII 800 with 128M RAM.
Description
In all data transfer operations, optimal performance is achieved when large data block sizes are transferred. Each transaction consists of a protocol stage, a drive spin stage and a fetch data stage. The larger the amount of data transferred in each transaction, the smaller percentage of time is spent on drive spin up and protocol. In normal operation, the most frequently used applications do not transfer large amounts of data. An example of this is browsing a directory structure. This can be done frequently and transfers, at most, 4k of data per transaction. Although all companies quote the highest data rate achievable, the customer will rarely see this performance. Their judgement of speed will be based on the speed during normal, small block size performance. This area has become of concern within the IEEE 1394 community. Protocol changes are being considered to reduce the time spent on the protocol phase of the transaction and so greatly improve small block size performance.
Optimal Performance
While testing the OXFW911, it has been noted that several factors influence the maximum speed obtained. The main factors are the operating system used, the drive speed and the OHCI card.
Conclusion
Customer perception of drive performance is determined during normal use. In most cases the data block sizes transferred are small. Therefore, increased performance at small block sizes will greatly increase the customers' perception of drive speed. The OXFW911 has been optimised in both hardware and firmware to take full advantage of the ARM7TDMI processor. This optimisation has resulted in excellent performance at small block sizes, this can be better then when the drive is connected internally. .
Optimisation of OXFW911
Oxford Semiconductor Ltd. 25 Milton Park, Abingdon, Oxon, OX14 4SH, UK Tel: +44 (0)1235 824900 Fax: +44(0)1235 821141
(c) Oxford Semiconductor 2000. OXAN 1 Application Note Revision 1 - December 2000 Part Numbers - OXFW911
OXFORD SEMICONDUCTOR LTD.
OXAN 1
Sequential Read Performance in UDMA4
40 35 Speed (Mbps) 30 25 20 15 10 5 0
1 2 4 8 16 32 64 128 256 512 10242048
On Internal IDE Bus Over IEEE1394 bus using OXFW911
Block Size (kB)
Figure 1 - IEEE 1394 Performance Vs Internal IDE Performance.
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OXFORD SEMICONDUCTOR LTD.
Contact Details Oxford Semiconductor Ltd. 25 Milton Park Abingdon Oxfordshire OX14 4SH United Kingdom Telephone: Fax: Sales e-mail: Web site: +44 (0)1235 824900 +44 (0)1235 821141 sales@oxsemi.com http://www.oxsemi.com
OXAN 1
DISCLAIMER
Oxford Semiconductor believes the information contained in this document to be accurate and reliable. However, it is subject to change without notice. No responsibility is assumed by Oxford Semiconductor for its use, nor for infringement of patents or other rights of third parties. No part of this publication may be reproduced, or transmitted in any form or by any means without the prior consent of Oxford Semiconductor Ltd. Oxford Semiconductor's terms and conditions of sale apply at all times.
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