Data Sheet

USBProtocolSuiteUserManual 253
RecordingOptions‐Misc.USB2.0 TeledyneLeCroyCorporation
5.4.1 Analyzer Trace Speed
ThisoptionsetsthespeedofthetrafficrecordedbytheAnalyzer.Thedefaultsettingis
Auto‐detect.ThissettingtellstheAnalyzertodiscoverwhatspeedtrafficisrunningand
tolabelpacketsaccordingly.Auto‐Detectwillfindaspeedandlockonitpermanentlyfor
thedurationofthetrace.Iftrafficspeedchanges,itwillnotbeseenbytheanalyzer.Ifyou
arehavingproblemswithyourrecordings,youmighttrysettingthetrafficspeedtoone
ofthefixedvalues‐‐Low,Full,andHispeed.Thesesettingsareusedwhenyouwantto
manuallysetthetrafficspeed.Itcantake~6msfortheHighSpeeddetectiontooccurin
Auto‐Detectmode,soitispossibletomisssomepacketswiththismethod.
Insomerarecases,auto‐detectioncircuitrycausesFullSpeeddevicestofailtoenumerate
onplug‐in.ChangingtheAnalyzerspeedtoFullSpeedcansometimessolvethisproblem.
Settingthespeedtooneofthefixedvaluesissometimesusefulfordebuggingpurposes.
Forexample,ifadevicethatisproducingnumerouserrorsataparticularspeed,youmay
wishtosettherecordingtothatspeedinordertoensurethattheAnalyzerdoesnot
misreadtheerrorpacketsandlabelthemthewrongspeed.Whileitisunlikelythatthe
Analyzerwillmislabelpacketsinthisway,manuallysettingtherecordingspeed
guaranteesthattheAnalyzeralwaysrecordspacketsatthecorrectspeed.
Whenselectingafixedspeed,theanalyzerwillstayonthatspeedregardlessoftraffic.To
capturemorethanonespeedrequiresloopingthroughmultiple2.0ports(USBTraceror2
daisychainedanalyzerssuchasVoyagerorAdvisorT3)
Notes on Hi-Speed Recordings
ErroneouschirpblockscanberecordedonanidlebuswhentheDevicehasitsFS
terminationsonwhiletheHosthasHSterminationsconnected.Thiscausesasmall
differentialvoltage(“tiny‐J”)ontheUSBbusthatcausesfalseChirpdetection.
Thisconditionoccursduringspeednegotiation:
 OnaHSbus,theconditionismomentaryjustbeforethedevicechirps.
 OnaCSbus,theconditionoccursbothbeforeandafterthedevicechirp(until
theendofReset).TheuserisdiscouragedfromusingSpeed=HIGHtorecordsig‐
nalsonaclassicspeedbus.
 TheAnalyzerstopsrecordinganythingfor2.5millisecondsfollowingaFS_Kstate
(whichisatleast2microsecondslong).Thisistoavoidpresenting“garbage”
whichisaby‐productofthehigh‐speedprobesettlingdown.