Copyright 2006 AN232B-03 Optimising D2XX Data Throughput Tab

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AN232B-03 Optimizing D2XX Data Throughput
Copyright 2006
AN232B-03 Optimising D2XX Data Throughput
Table Contents
Part D2XX Applications Optimizing Data Throughput Over
Introduction Transfer Sizes Driver Operation Optimizing Performance
Part Revision History, Disclaimer, Contact Information
Document. Revision History Disclaimer Contact Information
Index
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D2XX Applications Optimizing Data Throughput Over
D2XX Applications Optimizing Data Throughput Over
Introduction
This application note provides guidelines achieving optimal performance over from D2XX applications.
Copyright 2006
AN232B-03 Optimising D2XX Data Throughput
Transfer Sizes
maximum transfer size over setup once when device initialized. application change current transfer size value exceeding maximum transfer size. best transfer size application depends type. example, application that handles streaming data will more efficiently with large transfer size, whereas smaller transfer size more suited application that handles small amounts data.
Copyright 2006
D2XX Applications Optimizing Data Throughput Over
Driver Operation
D2XX device driver, maximum transfer size 64Kbytes. This necessary order support USB2.0 controllers: USB2.0, have found that transfer sizes greater than fail catastrophically. Current transfer size changed using function FT_SetUSBParameters. change comes into effect immediately, data that held driver time change lost. Note that, currently, FT_SetUSBParameters supports transfer size changes endpoint only, remainder this note restricted consideration read requests. When device opened, driver allocates buffers: transfer buffer maximum transfer size bytes read buffer whose size based same maximum transfer size. current transfer size default 4Kbytes, application setup current transfer size anytime after device been opened. driver performs requests size current transfer size, then copies data read buffer. actual request size determined space that currently available read buffer. read buffer becomes full (i.e. there enough space read buffer hold data returned from request), driver will stop issuing requests until space becomes available. Data removed from read buffer when application performs read request. rate which application issues read requests direct bearing driver's ability keep issuing requests. requests will continue issued long application performs enough read requests ensure that read buffer does become full.
Copyright 2006
AN232B-03 Optimising D2XX Data Throughput
Optimizing Performance
question setup application optimized data throughput complicated format data that transferred over USB. Data transferred over series byte packets. Each packets contains bytes that reserved FTDI bytes actual data. 4Kbyte transaction contains 3968 bytes actual data, 64Kbyte transaction contains 63488 bytes. general, byte transaction yields ((x/64)*2) bytes actual data. Optimized throughput occurs when maximum amount data transferred least possible number transactions. necessary condition that application's request size must matched current request size. More precisely, optimal throughput achieved when application request size multiple number actual data bytes contained current transfer size. example, using current transfer size 4Kbytes, optimal throughput achieved with application request sizes that multiples 3968 bytes. Maximum throughput achieved using current transfer size bytes, application requests that multiples 63448 bytes.
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Revision History, Disclaimer, Contact Information
Revision History, Disclaimer, Contact Information
Document Revision History
Version Release Date March 2004 February 2006 Comments Initial release. Format contact information updated.
Copyright 2006
AN232B-03 Optimising D2XX Data Throughput
Disclaimer
Copyright 2006 Future Technology Devices International Ltd. Neither whole part information contained product described this manual, adapted reproduced material electronic form without prior written consent copyright holder. This product documentation supplied as-is basis warranty their suitability particular purpose either made implied. Future Technology Devices International Ltd. will accept claim damages howsoever arising result failure this product. Your statutory rights affected. This product variant intended medical appliance, device system which failure product might reasonably expected result personal injury. This document provides preliminary information that subject change without notice.
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Revision History, Disclaimer, Contact Information
Contact Information
Head Office Glasgow, Future Technology Devices International Limited Scotland Street Glasgow United Kingdom Tel: 2777 Fax: 2758 E-Mail (Sales): sales1@ftdichip.com E-Mail (Support): support2@ftdichip.com E-Mail (General Enquiries): admin1@ftdichip.com Site URL: http://www.ftdichip.com Shop URL:
Branch Office Taiwan Future Technology Devices International Limited (Taiwan) 16-1, Sec. Mincyuan East Road Neihu District Taipei Taiwan Tel: +886 8791 3570 Fax: +886 8791 3576 E-Mail (Sales): tw.sales1@ftdichip.com E-Mail (Support): tw.support1@ftdichip.com E-Mail (General Enquiries): tw.admin1@ftdichip.com Site URL: http://www.ftdichip.com
Branch Office Hillsboro, Oregon, Future Technology Devices International Limited (USA) 5285 Elam Young Parkway Suite B800 Hillsboro, 97124-6499 Tel: (503) 547-0988 Fax: (503) 547-0987 E-Mail (Sales): us.sales@ftdichip.com E-Mail (Support): support2@ftdichip.com E-Mail (General Enquiries): admin1@ftdichip.com Site URL: http://www.ftdichip.com
Agents Sales Representatives Please visit Sales Network page FTDI site contact details distributor(s) your country.
Copyright 2006
AN232B-03 Optimising D2XX Data Throughput
Index
-BBuffers
-DD2XX Data Format
-FFT_SetUSBParameters
-IIN Endpoint
-MMaximum Transfer Size Maximum Transfer Size
-PPackets
-RRead Buffer Read Requests
-UUSB Controllers Request Request Size Transactions transfer Buffer Transfer Size
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