Application Note AN_112 VNC1L Data Transfer Speeds

Future Technology Devices International Ltd.
Application Note AN_112
VNC1L Data Transfer Speeds
Document Reference No.: FT_000099
Version 1.00
Issue Date: 2009-02-16
This application note explains the access times achievable with the VNC1L.
Future Technology Devices International Limited (FTDI)
Unit1, 2 Seaward Place, Centurion Business Park, Glasgow G41 1HH United Kingdom
Tel.: +44 (0) 141 429 2777 Fax: + 44 (0) 141 429 2758
E-Mail (Support): support1@ftdichip.com Web: http://www.ftdichip.com
Copyright © 2009 Future Technology Devices International Limited
Document Reference No.: FT_000099
VNC1L Data Transfer Speeds Application Note AN_112 Version 1.00
Clearance No.: FTDI# 88
Table of Contents
1
Introduction............................................................................................ 2
2
Data transfer speeds ............................................................................. 3
3
2.1
UART Transfers ................................................................................................... 3
2.2
FIFO Transfers ..................................................................................................... 3
2.3
SPI Transfers ....................................................................................................... 3
Contact Information............................................................................... 4
Appendix A - References ............................................................................ 6
Appendix B - Revision History.................................................................... 7
Copyright © 2008-2009 Future Technology Devices International Limited
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Document Reference No.: FT_000099
VNC1L Data Transfer Speeds Application Note AN_112 Version 1.00
Clearance No.: FTDI# 88
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Introduction
The VNC1L is a USB host controller IC which allows data to be transferred via a monitor port that can be
configured to be a UART, SPI or 8 bit wide FIFO interface to a USB device. This document will explain the
speed of such transfers when connected to a memory device.
Copyright © 2008-2009 Future Technology Devices International Limited
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Document Reference No.: FT_000099
VNC1L Data Transfer Speeds Application Note AN_112 Version 1.00
Clearance No.: FTDI# 88
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Data transfer speeds
2.1 UART Transfers
The VNC1L works at 12Mb/sec as all USB devices on a Full Speed USB bus must do. If it did not achieve
this then no USB device would ever work with it.
The actual throughput is not solely dependent upon the VNC1L but also on the device attached to the
USB port. Factors such as disk size, format and how full a disk is all impact on the overall speed as the
bulk of the processing time is related to handling the FAT table.
Performance testing is normally carried out at 115200 baud on the monitor port. However, additional
measurements with 3Mbaud data rate using a Flash disk with 4kB cluster size are recorded here.
The 3Mbaud UART data rate gives a theoretical PEAK data rate of around 272kB/sec. The peak data rate
is not indicative of the rate for sustained throughput due to the other overheads which are applicable to
this. The readings into theoretical, achievable, measured and sustained rates:
Maximum theoretical throughput: 272kB/sec
- UART interface is limiting factor
- 4kB transfer from UART to USB bus (16.775ms)
Maximum achievable throughput (without flash disk response time): 233kB/sec
- SCSI protocol overhead reduces theoretical throughput
- same 4kB transfer from UART to USB flash disk response time (17.588ms)
Maximum achievable throughput (with flash disk response time): 216kB/sec
- same 4kB transfer from UART to USB including flash disk response time (18.9ms)
Peak measured throughput: 159.4kB/sec
- File system overhead reduces achievable throughput
- 40kB file written in single block (40448 bytes in 253.66ms)
- Optimum file system conditions: with FAT table cached, DIR table cached, no file fragmentation, cluster
added in first sector of FAT table, DIR entry in first sector of DIR table.
Typical measured throughput: 25.45kB/sec
- 40kB file written in 512 byte blocks (40448 bytes in 1589ms)
- File system overhead increases with extra SCSI commands required
- Flash disk write response increases
- Optimum file system conditions: with FAT table cached, DIR table cached, no file fragmentation, cluster
added in first sector of FAT table, DIR entry in first sector of DIR table.
Reading data is faster as the VNC1L can store the data on the chip before passing to the monitor port.
Typical maximum rate is 200kbyte/s
2.2 FIFO Transfers
The peak and sustained throughputs of the FIFO interface at any given baud rate will be similar to the
UART interface at the same baud rate due to the architecture of the VNC1L device.
Reading data is faster as the VNC1L can store the data on the chip before passing to the monitor port.
Typical maximum rate is 400kbyte/s
2.3 SPI Transfers
The peak and sustained throughputs of the SPI interface at any given baud rate will be lower than the
UART interface at the same baud rate due to the architecture of the VNC1L device.
Copyright © 2008-2009 Future Technology Devices International Limited
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Document Reference No.: FT_000099
VNC1L Data Transfer Speeds Application Note AN_112 Version 1.00
Clearance No.: FTDI# 88
3
Contact Information
Head Office – Glasgow, UK
Future Technology Devices International Limited
Unit 1, 2 Seaward Place
Centurion Business Park
Glasgow, G41 1HH
United Kingdom
Tel: +44 (0) 141 429 2777
Fax: +44 (0) 141 429 2758
E-mail (Sales) sales1@ftdichip.com
E-mail (Support) support1@ftdichip.com
E-mail (General Enquiries) admin1@ftdichip.com
Web Site URL http://www.ftdichip.com
Web Shop URL http://www.ftdichip.com
Branch Office – Taipei, Taiwan
Future Technology Devices International Limited (Taiwan)
2F, No 516, Sec. 1 NeiHu Road
Taipei 114
Taiwan, R.O.C.
Tel: +886 (0) 2 8791 3570
Fax: +886 (0) 2 8791 3576
E-mail (Sales)
tw.sales1@ftdichip.com
E-mail (Support) tw.support1@ftdichip.com
E-mail (General Enquiries) tw.admin1@ftdichip.com
Web Site URL
http://www.ftdichip.com
Branch Office – Hillsboro, Oregon, USA
Future Technology Devices International Limited (USA)
7235 NW Evergreen Parkway, Suite 600
Hillsboro, OR 97123-5803
USA
Tel: +1 (503) 547 0988
Fax: +1 (503) 547 0987
E-Mail (Sales)
us.sales@ftdichip.com
E-Mail (Support) us.support@ftdichip.com
Web Site URL
http://www.ftdichip.com
Branch Office – Shanghai, China
Future Technology Devices International Limited (China)
Room 408, 317 Xianxia Road,
ChangNing District,
ShangHai, China
Tel: +86 (21) 62351596
Fax: +86(21) 62351595
E-Mail (Sales): cn.sales@ftdichip.com
E-Mail (Support): cn.support@ftdichip.com
E-Mail (General Enquiries): cn.admin1@ftdichip.com
Web Site URL: http://www.ftdichip.com
Copyright © 2008-2009 Future Technology Devices International Limited
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Document Reference No.: FT_000099
VNC1L Data Transfer Speeds Application Note AN_112 Version 1.00
Clearance No.: FTDI# 88
Distributor and Sales Representatives
Please visit the Sales Network page of the FTDI Web site for the contact details of our distributor(s) and
sales representative(s) in your country.
Vinculum is part of Future Technology Devices International Ltd. Neither the whole nor any part of the information contained in, or the
product described in this manual, may be adapted or reproduced in any material or electronic form without the prior written consent of
the copyright holder. This product and its documentation are supplied on an as-is basis and no warranty as to their suitability for any
particular purpose is either made or implied. Future Technology Devices International Ltd will not accept any claim for damages
howsoever arising as a result of use or failure of this product. Your statutory rights are not affected. This product or any variant of it is
not intended for use in any medical appliance, device or system in which the failure of the product might reasonably be expected to
result in personal injury. This document provides preliminary information that may be subject to change without notice. No freedom to
use patents or other intellectual property rights is implied by the publication of this document. Future Technology Devices International
Ltd, Unit 1, 2 Seaward Place, Centurion Business Park, Glasgow, G41 1HH, United Kingdom. Scotland Registered Number: SC136640
Copyright © 2008-2009 Future Technology Devices International Limited
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Document Reference No.: FT_000099
VNC1L Data Transfer Speeds Application Note AN_112 Version 1.00
Clearance No.: FTDI# 88
Appendix A - References
Document Reference
DS_VNC1L-1A
Description
Vinculum Embedded USB Host Controller IC Data Sheet
http://www.ftdichip.com
Copyright © 2008-2009 Future Technology Devices International Limited
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Document Reference No.: FT_000099
VNC1L Data Transfer Speeds Application Note AN_112 Version 1.00
Clearance No.: FTDI# 88
Appendix B - Revision History
Revision History
Version 1.00
Initial Release
February, 2009
Copyright © 2008-2009 Future Technology Devices International Limited
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