Packet-Master Data Sheet 2.3
Contents
1. NE Event 14533 Start of RESET Duration End of RESET IDLE Field Value Meaning 6 911 034 5 10 682 us FULL SPEED LINK 1 000 us g bLength valid Length S Control Transfer Addr Endp Data 18 bytes Status bDescriptorType DEVICE Precise 6 973 409 s Get Device Descriptor 0x00 00 12 01 00 02 02 00 00 40 bedUSB 0x0200 Spec Version timina for gt Event 15063 Start of RESET Duration End of RESET IDLE bDeviceClass Ox02__ Comms and CDC Iming To ok 110 922 us FULL SPEED LINK 1 000 us bDeviceSubClass ox0O at cnn every event ay Control Transfer Addr Endp Data 0 bytes Status aD ere IEEE 0x00 Set addres maloo oO Tok bMaxPacketSize0 64 Max EPO Packet Size Max Custom Control Transfer Addr Endp Data 18 bytes Status Get Device Descriptor O02 0x0 12 01 00 02 02 00 00 40 OK z filter o idProduct 0xD039 Unknown Vv Control Transfer Addr Endp Data 9 bytes Status bedDevice 0x0000 Device Release No r Set Configuration Descriptor 002 00 0902 4F 010A 0208 80 OK TETT EEEE Strin Bookmarks o Control Transfer Addr Endp Data 4 bytes Status Product 2 J d Product Stri for fast event Get String Descriptor O 002 00 0403 0904 OK ee Adil EOR SUNE Ea location C seTuP 002 oo e006 00 03 00 00 FF oof ACK POTA OTIORNIE 12 01 00 02 02 OO OO Event 21007 SETUP Adar Enap cRCS EOP 20 BENE so bo oo oc 7103 207 z aoooooa od 002 oo oas oz o ee L 1 UZ Ls LJ Bandwidth 109 C HO2. View By Control Transfers less significant events filtered re 2618 HS Control Transter Addr Endp Data 18 bytes Status 55952 3815 42 Get Device Descriptor 0x00 0x0 12 01 00 02 00 00 00 40 Event 2621 Har da LL 55953 0595 A T 3 4100 us 2522 4072 HS ee 5 A Succeeded O 4945 4351 GE Control Transfer Addr Endp Data 0 bytes Status 56 129 44 5 F Set Addres 00n oon oof 0k Fo2O0G SSG HS Control Transter Addr Endp Data 18 bytes Status S6 174 119 5 4 Get Device Descriptor 001 00 14204 0002 00 000040 Ok robo 4705 Control Transter Addr Endp Data 39 bytes 5 56 172 158 s 42 Get Configuration Descriptor Ox04 0x0 09 02 27 00 04 041 00 80 ror 10 5994 i Control Transter Addr Endp Data 34 bytes Z 56 173 132 s 1 cet Sting Descriptor 3 001 00 22 03 34100 36 00 4400 By clicking on the filter buttons for less significant events the sequence of top level control transfer header rows may be viewed in isolation This ability to view information at an appropriate level of complexity makes GraphicUSB an invaluable tool for getting straight to the heart of the subject Packet Master Data Sheet 2 3 T Copyright 2006 2009 MQP Electronics Ltd m Pack ELECTRONICS Full Analysis and Data Panes By clicking on an event row in the event pane a complete analysis of the event is displayed in the analysis pane and the data content is shown in its entirety in the data pane Whe
3. In a similar fashion it is theoretically possible to use the same host computer for the Packet Master Analyser and for the Host Under Test We do not recommend this but if it is absolutely unavoidable then you must at least use a separate USB host controller for the device under test If your computer does not have two host controllers then you will need to buy a plug in USB host controller card Packet Master USB480 and USB500 AG must be connected to a High Speed host Packet Master Data Sheet 2 3 14 Data Sheet Generator The USB500 AG when used as a generator should be connected as shown below can be same computer Pie PE Host for Hast for Generator Analyser WISBS500 AG Used As Analyser r USB500 AG sed As Generator Recommended for Voltage f current measurement Generator Ernulates Hast Device Under In this example a second USB500 AG is used as an analyser to capture the resulting traffic The device under test could be replaced by a host under test with the generator emulating a device It could also be replaced by an OTG A or B device Copyright 2006 2009 MQP Electronics Ltd q P ELECTRONICS Specifications Minimum System Requirements for Packet Master Host e Pentium 3 600MHz e PC with High Speed USB port should be dedicated to the capturing Actual target device should be connected to a different Host Computer to ensure reliable capture
4. bandwidth e Windows Vista or XP Service Pack 1 or better 32 bit or 64 bit e CD ROM DVD Drive e 1GB RAM 100MB space on Hard Disk Note A good performance machine is recommended for good capture rate Physical Specification P USB480 USB500 AG Weight 155g 360 g 400 g Dim 129 x 100 x 190 x 140 x 190 x 140 x l 31 mm 32 mm 52 mm 20 80 20 80 20 80 non non non condensing condensing condensing Safety etc CE compliant Electrical Requirements The Packet Master analyser normally derives its power from the Host computer s USB connection 150mA from USB host Power USB12 Optionally zero mA from USB if powered externally 225mA from USB host Optionally zero mA from USB if powered externally 350mA from USB host Optionally zero mA from USB if al USB500 powered externally Power USB480 External powering mandatory when used as generator Packet Master Data Sheet 2 3 Data Sheet Signals Available on Feature Connector USB480 USB500 AG RXVALID RXACTIVE 60 MHz Clock Decoded Data Decoded Clock Packet Sync Detected Standard Accessories Packet Master Analysers come complete with the following e GraphicUSB control software on CD e USB 2 0 cable x 2 e Manual on CD e External Power Supply USB500 AG only Optional Accessories e External Power Supply Software Options e Various class analysis options GraphicUSB Devkit A comprehensive User Manu
5. to the starting out developer The Packet Master analyser will allow you to examine the sequences for any Operating System Host Controller combination of your choice This will allow you to reveal any false assumptions you may be making that a particular enumeration sequence is standardised As a device developer just remember that the device should make no assumptions about enumeration sequences but simply respond correctly to any request it receives Packet Master Data Sheet 2 3 Data Sheet Examine Working Devices A great benefit available from the Packet Master analyser is that it allows you to examine exactly what transactions occur in a working device perhaps manufactured by a third party This may reveal your own bad assumptions about how a protocol works or may show you how many devices on the market do not obey the rules Some operating systems have work arounds for certain common protocol errors and you may discover some of these first hand Specifications often contain ambiguities For example without seeing it for yourself you might not have realised that there have been two different ways of encoding the version number bcdUSB for USB 1 1 Operating systems appear to take the pragmatic approach of accepting either Fine tune Performance Much of the effort in developing a new device will go into achieving the throughput required There is no substitute for seeing the transactions attempted by the h
6. Start Button Manual e BNC Socket Input On Condition e BNC Socket Input Off Condition e Any of four specified Token Packets e Any of four specified Data Packets e Any of four specified Split Packets e ACK Packet e NAK Packet e STALL Packet e NYET Packet e Not Handshake Packet any event other than ACK NAK STALL or NYET packet e ERR Packet e PRE Packet e Specified SOF Packet e Reserved PID Packet e Bus Reset e Suspend e Resume e HS Handshake OK e HS Handshake Fail e Chirp e Keep Alive e Data Line High e Data Line Low e Vbus On Packet Master Data Sheet 2 3 12 Data Sheet e Vbus Off e Specified Error Condition e Any of four sequences of up to four of the above events occurring consecutively e A counted quantity up to of any of 65535 of any of the above e A set of up to four of any of the above which occur in a particular order though not necessarily consecutively Triggering Presets In order to allow fast trigger setup a number of presets are provided to cover common triggering requirements to act as a starting point for more complex settings or simply to demonstrate how typical triggering requirements can be set up e Triggering OFF e Manual Triggering e Trigger on any Transaction e Trigger on any Data Packet e Trigger on Bus Reset e Trigger on Preamble with Setup Transaction e Trigger on Isochronous In Transaction e Trigger on isochronous Out Transaction e Trigger on In
7. be printed e Standard software and firmware up grades are free of charge from our web site e Software can be freely used as a viewer in the absence of the Analyser Hardware e A multi document interface allows comparison between captures e Capture size only limited by host computer RAM size e Export any range of events to text file with a chosen level of filtering e Export all or chosen descriptors as annotated source code e Export data from a selected event or a range of events e Custom event filter e Captures can be controlled from another application e Optional Class Analysis modules Packet Master Data Sheet 2 3 6 Copyright 2006 2009 MQP Electronics Ltd mMm Data Sheet ELECTRONICS Mixed Speed On Single Link Poe 3125 7 101955 eS ef IN E ont Td Event 3122 Syne PREJ Hub suf LS Syne IN Addr Ende CROCS EOP IDLE 71019555 00000001 Ox3C 0 69 us 4 00000001 069 003 01 01C 1 33 us Event 3123 fe Se IDLE 7 104 984 5 oo000004 O54 1 417 us This view of part of a screen shot from Graphic USB shows a representation of data being transferred at two different speeds on the same link Each packet is preceded by a coloured marker indicating Full Speed or Low Speed This makes the function of the PREAMBLE packet very clear Each Event has a precise timestamp left Notice also the detailed timing information for Hub Setup time End Of Packet duration and IDLE state time
8. or Out Transaction e Trigger on Ping Transaction e Trigger on Split Setup Transaction e Trigger on Split Bulk In or Out Transaction e Trigger on Split Interrupt In or Out Transaction e Trigger on Split lsochronous In or Out Transaction e Trigger on Specified Data Pattern e Trigger on Chirp e Trigger on Suspend or Resume e Trigger on Error Condition Copyright 2006 2009 MQP Electronics Ltd L P ELECTRONICS Data Sheet G3 GraphicUSB OTG_A_device mgen E File Edit View Operations Window Help Hin AEM EHESS a J IERI i tel FF 3 EB py Sy ay ay gat Vous m Generator Seceript File LECH HETATHETEE OTG A DEVICE ttt eee a es FileType MOPGEN 1 EmulationMode ADEVICE STANDARD ControlMode HOST POUERR UP ESTABLISH Fa LINE Retries SAMEFRAME or NONE or NESTE Vhuson WaitPullupoOn FULLSPEED suspend 116 Reset 20000 Idle 9303 SOFOn 7 SOFS 65 ttt Get Device Descriptor from adc Idle 7500 sendPacketFs SETUP Ab EP C500 OO Idle 10 sendPacketFs DATAO 0x50 0x06 OxOO0 OxOL1 OxO0 OxOO0 OXx4C CRC1i6L CRC16H WaitPacketFs ACK Packet Master Data Sheet 2 3 Generator Software Features e Generator can emulate standard USB or an On the Go A device or B device e Generator can emulate a device or a host and can switch between them for On the Go e Generation controlled from Packet Master unit or from GraphicUSB screen e Generator
9. programs can be up to 64MB in size e Generator Script language uses intuitive commands e Generator scripts can be directly exported from any Packet Master analyser capture file e Pre defined common script sequences can be directly inserted into script A single button click can save and compile the script download it to the generator and start it running Intelligent transaction retry modes If you have a Packet Master generator and a Packet Master analyser you can control them both from the same GraphicUSB screen e Standard software and firmware up grades are free of charge from our web site e A multi document interface allows scripts and captures to be open at the same time 13 Copyright 2006 2009 MQP Electronics Ltd q P ELECTRONICS Test Set up Connections Analyser To achieve a good capture rate it is important to provide a suitable test environment The Packet Master Analyser should be hosted by a good performance PC with a high speed USB connection This USB host controller should not be shared by any other USB device while doing the testing PC Host for Analyser High Speed USB Link Packet Master Analyser r Device Under Tast Hast Under tes USB Link Under Test The Packet Master USB12 will function correctly when connected to a Full Speed link but the capacity will be severely reduced and only low rates of USB traffic may be captured from the device under test
10. C T10 Project 1240 D e SFF 8020i MMC 2 ATAPI e QIC 157 e USB Floppy Interface UFI e SFF 8070i e SCSI transparent command set e Bulk Data Transfers e Notification Interrupt Transfers Printer Class e Class Requests e Bulk Data Transfers Vendor Class user definable analysis e Class Requests e Data Transfers Test and Measurement Class e USBTMC e USB488 e Class Requests e Bulk Data Transfers e Notification Interrupt Transfers Video Class V1 0 e Video Control e Video Streaming e Class Descriptors e Class Requests e lsochronous Streaming Data Transfers e Bulk Streaming Data transfers e Notification Interrupt Transfers Video Class V1 1 e Video Control e Video Streaming e Class Descriptors e Class Requests e lsochronous Streaming Data Transfers e Bulk Streaming Data transfers e Notification Interrupt Transfers 11 Copyright 2006 2009 MQP Electronics Ltd L P ELECTRONICS Advanced Triggering The Packet Master USB480 and USB500 AG are provided with an advanced trigger capability Capturing can be triggered by a wide range of possible events or sequences of events as listed below The Pre trigger Buffer can be set to a range of sizes up to 4Mbytes and can capture events which occurred before the trigger point This allows analysis of events which lead up to a particular situation which needs to be investigated Events Available For Triggering e Any Event e
11. Class Descriptors e Class Requests e lsochronous Streaming Data Transfers e MIDI bulk transfers Audio Class V2 0 e Audio Control e Audio Streaming e MIDI Streaming e Class Descriptors e Class Requests e lsochronous Streaming Data Transfers e MIDI bulk transfers e Notification Interrupt Transfers Comms and CDC e CDC Data e Direct Line Control Model e Abstract Control Model e Telephone Control Model e Multi channel Control Model e CAPI Control Model e Ethernet Networking Control Model e ATM Networking Control Model e Wireless Handset Control Model e Device Management Model e Mobile Direct Line Model e OBEX Model e Class Descriptors e Class Requests e Ethernet Link Layer encapsulation ARP RARP IP Datagrams TCP UDP and IGMP headers etc e Obex V1 3 protocol Packet Master Data Sheet 2 3 Human Interface Device HID Class e Class Descriptors Report Physical e Class Requests e Report Interrupt Transfers Hub Class e Hub Class Descriptor e Class Requests e Notification Interrupt Transfers Image Class and Media Transfer protocol MTP e Class Requests e Bulk Data Transfers e PIMA 15740 Operation Interpretation e PIMA 15740 Data Interpretation e PIMA 15740 Response Interpretation e MTP Extensions e MTP Enhanced Extensions e Event Interrupt Transfers Mass Storage e Class Requests e Bulk Transport Only e Control Bulk Interrupt CBI Transport e RB
12. L P ELECTRONICS Data Sheet Packet Master USB12 and USB480 Bus Analysers Packet Master USB500 AG Bus Analyser Generator The Packet Master USB12 is a Hardware USB Bus Analyser intended for development of Low and Full Speed USB devices and hubs etc The Packet Master USB480 adds High Speed capability together with On The Go analysis and Advanced Hardware Triggering The Packet Master USB500 AG adds USB Generator Capability and a Vgus Monitor function All come complete with our Windows application GraphicUSB for capturing and displaying every detail of the data interactions on a USB link Packet Master USB12 USB480 and USB500 AG Packet Master Data Sheet 2 3 Take Control of your USB Development Chapter 9 of the USB Specification details some seventeen Standard Device Requests which must be correctly implemented in any USB device in order for the device to be successfully enumerated by the host controller When developing a USB based device it is a major undertaking to implement the basic Chapter 9 Framework correctly as enumeration will simply fail for any number of reasons involving incorrect responses to the requests There is no substitute for a USB bus analyser for revealing the smallest details of the packet transfer taking place on the bus Software based analysers can only ever give you a partial picture of what is going on usually not reporting at all the packets with the errors The Packet Ma
13. MQP Electronics Ltd mMm qj J Data Sheet ELECTRONICS Comparison Chart Packet Master ia ae Chart usB4so USB500 AG Analyser Generator High Speed Start Stop Controllable From Unit S Full Speed NINS Chirp Analysis INR FIFO Buffer 4 Mbyte 4 Mbyte Class Analysis Options Available BNC Trigger NS S RRNA External Power Supply Provided Packet Master Data Sheet 2 3 4 Copyright 2006 2009 MQP Electronics Ltd mMm Data Sheet ELECTRONICS Software Overview The Packet Master Analyser owes a large part of its functionality to the GraphicUSB application supplied with the unit A simple yet information rich display allows you to view every detail of a capture The latest version is always available free of charge from our website This shows the organisation of the screen after a typical capture Event pane reveals every detail of Any selected event is data and timing which occurs on thoroughly analysed in the bus You see exactly what the details pane happened in graphic detail Highlighting an item VBUS monitor display locates its data in the data pane below amp 4 GraphicUSB k800i_2 mqu Sele Filt er out ess File Edit View Operations Window Help or X La significant eeu S in AARAA D G vbus 4 96v 0 000ua events in 14489 14531 Control Transfer Addr Endp Data 0 bytes Status configurations A USB device has only one device gt E E descriptor
14. Sheet 2 3 Copyright 2006 2009 MQP Electronics Ltd q P ELECTRONICS Optional Class Analysis Modules A number of Class Analysis Options are available These include e Human Interface Devices HID Class e Hub Class e CDC and Comms Class e Mass Storage Class e Audio Class e Image Class and Media Transfer Protocol MTP e Printer Class e Smart Card Class e Video Class e Test and Measurement Class e Wireless Controller Class e Vendor Class Each option is available individually Registering an option allows Graphic USB to display a full analysis of the specific Class transfer The screen shot to the right shows the analysis of a HID Report Descriptor Packet Master Data Sheet 2 3 Data Sheet amp Control Transfer Get HID Report Descriptor Meaning Usage Page Generic Desktop Controls cm Pe D Bia co La co he Collection Application Usage Pointer Collection Physical Usage Page Button Usage Minirmurm 14 Usage Maximum 5 Logical Minimum 0 Logical Maximum 1 Report Count i5 Report Size 14 Input Data Variable Absolute Bit Field Report counti Report Size 3 input constant Array Absolute Bit Field Usage Page Generic Desktop Controls Usage tai Usage vi Usage Vvheell Logical Minimum 12r Logical Maximum 127 Report Size 8 Report Count 3 input Data Variable Relative BitField 181 End Collection End Collection i I gt a j cy
15. UT MIN NAKs Filtered usage at z z i any point in i E ae ee anf ile time Bandwidth Utilisation 200 000 000 s lt For Help press F1 622608 events Timeline view Zoom in to a single packet Packet Master Data Sheet 2 3 5 Copyright 2006 2009 MQP Electronics Ltd mMm qj J Data Sheet ELECTRONICS Analyser Software Features e Capture controlled from Packet Master unit or from GraphicUSB screen e Triggering on user definable event sequences including BNC connector input not USB12 e Adjustable Pre Trigger Buffer size allows capture of up to 32 Mbytes of event data prior to trigger point not USB12 e Captured document shows every detail of data transactions graphically for a fuller understanding of the USB protocol This includes a detailed visual analysis of each packet e Transactions are grouped and summarised with a header row in the event pane Transfers are summarised with a special header row e Filters allow less significant information to be removed from the display to allow you to concentrate on the critical data e Each event is analysed in detail with any significant features explained and possible errors or warnings highlighted e Data pane shows the data content of any packet e Detailed timeline and bus bandwidth usage pane e Bookmarks can be set on events of interest to allow them to be quickly located e Comprehensive search functions e Events display detail analysis or data can
16. al is available for download from our website The GraphicUSB application together with some sample captures can also be downloaded For further information contact MQP Electronics Park Road Centre Malmesbury Wilts SN16 OBX UK Tel 44 0 1666 825 666 Fax 44 0 1666 825 141 email sales mqp com web site http www mqp com Copyright 2006 2009 MQP Electronics Ltd
17. co _ _ I 2 j co n o f oo on gt co oy co Cp i i co he i co g oo q co 1p Pony on a a a a a E n j 2n J i p Cc hu g 0 i T oo DJ m co oc DJ m imn DI co ha myn Jj OO q LT L mo oo in co DJ co Oy Usage Mouse Wi D j co 9 Copyright 2006 2009 MQP Electronics Ltd L P ELECTRONICS Input Report Usage Bits With the HID Class Analysis enabled each HID report is identified and the contents analysed Examining the analysis of existing devices is an excellent way to learn how a class works and it has never been easier to reveal the building blocks than with Graphic USB Packet Master Data Sheet 2 3 10 Data Sheet The shot to the left shows the results of the built in HID Report Descriptor parser Each report defined by the Report Descriptor is identified and displayed il Interrupt Transfer Device To Host This is a HID IN report An analysis of the report contents appears below In Report Value Butona 0 Butona 0 ene a Buttons J0 Wheel do Data Content OO FE FF OO Copyright 2006 2009 MQP Electronics Ltd q P ELECTRONICS Data Sheet Class Analysis options currently supported by all Packet Master Analysers Audio Class V1 0 e Audio Control e Audio Streaming e MIDI Streaming e
18. ecise conditions A pre trigger buffer can capture up to 32MB of events before the trigger point A BNC Trigger socket on the rear panel can be used as input or output in conjunction with the triggering under software control Packet Master Data Sheet 2 3 Data Sheet Packet Master USB500 AG In addition to the capabilities of the USB480 the USB500 AG analyser can also be configured as a USB generator In host mode it provides the Vgus supply applies bus states and sends packets and waits for responses all under control of your script In device mode it emulates plug in waits for the appropriate bus states and packets and responds with the required data all exactly as you specify To see the detailed interactions on the bus use any USB analyser The advantage of using a Packet Master unit for the analyser is that the powerful GraphicUSB application is able to control both the analyser and the generator simultaneously Veus Monitor Whether configured as an analyser or as a generator the USB500 AG continuously displays the Vegus voltage and current G3 GraphicUSB _ mouse_ls mqu File Edit View Operations Window Help o sho B e lt gt F vbus 4 617 52 08mA al Min 5 24 SF 6 2 045 0416 s gt Led 24 36 da 2 oo E Copyright 2006 2009
19. ost together with the device s response to them Armed with this valuable information you will be in the best position to be able to fine tune your device s performance Packet Master Generator Benefits Emulate any host or device sequence With a Packet Master Generator you no longer have to persuade your host computer to produce a rare situation for testing your device Write a simple script and the generator will do the rest If you want to Know what happens when a transaction occurs which your host never seems to send simply write a script and find out Copyright 2006 2009 MQP Electronics Ltd q P ELECTRONICS Packet Master USB12 The USB12 provides the most economical solution to Low Speed and Full Speed USB bus analysis An ideal introduction to USB development it is USB Bus Powered for convenience of use via a High Speed USB 480 Mb s connection to a host PC Integral Capture Start and Stop buttons and Capture Indicator allow captures to be controlled from the unit or from the GraphicUSB application The link under test connects passively through the front panel USB connectors A rear panel feature connector provides signals for oscilloscope or logic analyser Packet Master USB480 KEV Ba The USB480 adds the capability of High Speed USB analysis In addition a 64 MB FIFO prevents loss of data Advanced triggering capability allows captures to be automatically started by a selected set of pr
20. re relevant any information selected in the analysis pane is highlighted in the data pane for easy identification All standard requests and descriptors are analysed in detail Discrepancies are described Timeline and Bandwidth Pane il Control Transfer Data Sheet Get Device Descriptor 4 device descriptor describes general information about a USB device It includes information that applies globally to the device and all of the device s configurations A USB device has only one device descriptor Field Value Meaning bLength Valid Length bDescriptorType DEVICE Interface Descriptor Interface Descriptor Interface Descriptor idPraduct 02168 Transcend JetFlash 2 07 Astane JSE Orive Ox0200 Device Release Mo iManufacturer 1 Index to Wanutacturer String Index ta Product String iSerialbMumber 3 Index to Serial Mumber String bNum onfigurations 1 Number of Possible Configurations Data Content i Ol loo oz oo oof oOo 40 AO OF 66 21 00 z O1 Oe 03 O1 Timeline view zooms in to reveal individual packets within the frames Bus usage is indicated by bandwidth utilisation histogram 100 M OUT We IN 0 TT el l l 1 l l ot 34 491 000 lt 12 8 bytes OUT 16 bytes IN Bandwidth Utilization EE RE a O OE E E I l O ee ee Il oe en D 34 492 000 5 34 493 000 Z 1 oe ee 34 495 000 1 rt tu 34 454 000 For Help press Fl et Master Data
21. ster Analyser connects passively between a host computer and the USB device and captures all USB activity without influencing the link Copyright 2006 2009 MQP Electronics Ltd q P ELECTRONICS Packet Master Analyser Benefits Save Development Time The Packet Master analyser will provide you with exact information showing you at which point a device under development is failing It will save you weeks of wasted development time In many cases you will find that the error you are looking for is highlighted on the GraphicUSB display in a distinctive colour Simple Connection The Packet Master analyser connects passively between a host computer and the USB device and captures all USB activity without influencing the link So you can be sure that you are seeing exactly what really happens All the important timings are displayed Understand USB When it comes to the USB protocol a picture is worth a thousand words The graphical display of GraphicUSB immediately provides deeper understanding of the data transfers and their related timings By examining a working device you will learn more in a few minutes than from hours of reading the specifications Specifications are essential too but easier to understand when you have a picture in your mind Understand Host Command Sequences There is no specification as to the sequence of commands which a device may expect from a host Some command sequences can be very surprising
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