SMT servo.c Program. Tom Sargent

Transcription

1 SMT servo.c Program Tom Sarget Itroductio: The servo.c program resides o the "smtots" Liux-hosted computer. This machie has PC104 iterfaces to the Traquair (Hut) HEPC2104 DSP processor which i tur has the A/D iterfaces which read the outputs of the SMT shaft ecoders. Every 10ms (omially) the DSP processor seds a positio report to the smtots computer which the servo.c program reads. The smtots machie also has ISA bus parallel I/O ports ad other A/D ad D/A iterfaces which iterface to the Krupp rack ad other SMT cotrol elemets. The servo program also receives positio commads from the tracker program (which also rus o smtots). These describe where the telescope should be poitig as a fuctio of time. With all this iput, the servo program is able to read 1- the actual telescope positio, 2- telescope status, ad 3- the desired telescope positio. The differece of the actual ad desired positio is the istataeous trackig error. Kowig the sig ad magitude of this error, it ca compute a correctio sigal to the telescope drive to make it follow the desired track. The oly output to the telescope cotrollig its positio from momet to momet is a velocity sigal for each axis, so this system is a "velocity loop" servo. The program costatly adjusts the azimuth ad elevatio velocities to keep the telescope poited at a desired object as it moves across the sky. The velocities are expressed to the hardware as a +-10v sigal which servo geerates by usig a ISA bus module which has two 16-bit D/A coverters. While cotrollig the telescope positio, the servo program at the same time moitors its iputs for commads from the operator or other programs, ad for sigals idicatig various failures or usafe coditios, such as limit switches beig closed, excessive electrical currets, etc. It ca alert the operator or stop the telescope if a serious problem is detected. Ultimately all commads that move the telescope, regardless of where they origiate, ed up beig performed by servo. The HEPC2104 DSP processor. See a separate documet for a detailed descriptio of the DSP-residet program. The Liux system uses a driver from Traquair/Hut which is called hep2e. It is able to ru the ISA bus iterface which coects to the DSP processor card s comport 4. The DSP is a Texas Istrumets 320c44 chip. The servo program ca talk to the hep2e driver directly by doig reads ad writes to the driver, or it ca use the Hut Applicatio Program Iterface (API) software to do the reads & writes to the DSP. The API software i tur calls that same hep2e driver. It was foud that the Hut API uses asychroous I/O ad this has the side effect of spawig hudreds of tasks per secod. Apparetly it Page 1 servo.c rev. 1.06

2 does oe for each I/O read or write. So, it is recommeded to NOT use the Hut API. The use of the Hut API is cotrolled through coditioal compilatio. Defie USE_HUNT_API i servo.c ad recompile it, if you wat the program to use the Hut API software. This is ot recommeded. Compilig the servo program The servo program is compiled from 6 C files (servo.c, geomet.c, shell.c, servoutil.c, servoshow.c, ad checksu.c) which are i the cactus/tracker/ directory. See the Makefile i that directory. So, simply typig "make servo" will do the ecessary compilatio ad likig to produce a executable "servo" file. There is oe further step required, though. This step chages the owership of the servo executable file so that the program starts up as root. It eeds to do this so that it ca do the ecessary system calls to chage its Liux scheduler so that it rus with priority schedulig (SCHED_FIFO) rather tha the default Liux schedulig. This gives servo higher priority ad allows it to have cotrol of the processor a larger fractio of the time. It makes it more real-time. The servo program will ru if this step is skipped, but it will evetually (o a time scale of a day or so) eglect the flow of data from the DSP processor for so log (2 sec.) that the program will halt. To adjust the privileges o servo so that it ca chage its scheduler successfully, after the ew servo file is created (by "make servo"), the programmer has to become root. The ru a script i the tracker/ directory called "servopriority". This script will have o effect if the user who ivokes it is ot root. Remember to do a ^D afterwards to stop beig root. Issuig commads to the servo program The servo program ca be cotrolled by the operator maually either from a socket message or from a xterm widow. It ca be cotrolled from other programs via socket messages which they ca sed to it. The program icorporates a simple commad parser ad it keeps lookig for lies of ASCII text iput for the parser to process. There are aroud 50 differet commads. The program ow (after july 2002) watches both sources of iput (stdi ad sockets) at all times. The commad parser uses reverse polish sytax. A iput lie cosists of commad ames ad/or umeric argumets delimited by blaks. It starts at the left ed of the lie ad parses out "words". A word is either a literal iteger umber, a predefied commad ame, or a mistake. Those are the oly 3 possibilities. If the word is iterpretable as a iteger umber, the equivalet biary umber is computed from the ASCII text ad that value is pushed o the parser s parameter stack. If the word is a commad ame matchig oe of those i the commad ame list, the the associated commad fuctio is executed. All commads that take argumets, expect to take those argumets off the parameter stack. This is what eforces the reverse polish sytax, that is, the argumets must precede the commad ame o the lie. Oe feature that devolves from this is that multiple commads ca be typed i the same lie. It s a especially simple way to parse commads. For example, the commad to prit out some diagostic status iformatio is called st. To ivoke it, just type those two characters followed by a carriage retur. st takes o argumets. 0-> st Page 2 servo.c rev. 1.06

3 The "0->" is the prompt prited by the servo program. The digit, 0 i this case, is a cout of the umber of umbers o the stack at the momet. The prompt is visible oly from the shell. Programs or users commuicatig with it via sockets will ever see a prompt. As aother example, the track commad takes 2 argumets. They are flags for azimuth ad elevatio drives. The commad 0-> 1 1 track tells it to start trackig i both azimuth ad altitude. 0 0 track would halt trackig i both axes. The first argumet is the flag for azimuth ad the secod is for elevatio. So 0 1 track would disable trackig for azimuth ad eable it for elevatio. Note the blaks separatig the literal umbers. The commads are listed i a array i shell.c called commads. They are summarized i appedix 1 of this documet. Report processig Normally the servo program is hug i a fuctio called getreport() pedig o a read from the DSP. The DSP seds a positio report every 10ms (omially, this ca be chaged dyamically). This is a log time compared to the time it takes servo to remove a report from the hardware FIFO ad act o it, so usually the hardware FIFO betwee the DSP ad Liux is empty. Whe servo does a read from the hep2e driver (via a call to api_read()) ad the FIFO is empty, the call hags util the DSP writes some report to its comport. That should ot be more tha 10ms. servo always sets a alarm prior to each read from the hep2e driver so that if the read hags for more tha 2 secods without receivig a report from the DSP, Liux calls servo s timeout() fuctio which executes a shutdow routie to stop the telescope. Whe the tracker task wats to sed a ew polyomial to servo, it does so by doig a special ioctl call to the IRIG driver. I this call it supplies the two 2d order polyomials which specify the azimuth ad elevatio track as a fuctio of time which the telescope should follow for the ext 10 secods. The driver saves this iformatio i its local memory. The ext time the IRIG driver receives a read commad specifyig a read legth equal to that of the struct COEF_CMD (as opposed to the usual struct TS_TIME), it icludes the latest polyomials i that COEF_CMD structure alog with the curret time. Reads of this type happe at least every 10 ms. If the read is the first oe after a ew polyomial has bee specified by tracker, tracker will have set the ew flag i that structure to 1 idicatig that it has a updated polyomial. If it is also for a ew positio (i.e., chage of object or beam switch) the the ew flag is set to 2 (this is doe i sedservo() i traksub.c). This is true for oly that oe read; o very ext read (10ms later) with that same legth, the IRIG driver will have the ew flag set to 0 agai. This scheme is a hold over from the 12 meter telescope s cotrol system (except for servo.c most of the SMT cotrol software is take from the 12 meter telescope). Note that because of this behavior of the IRIG driver, o other process should do IRIG reads with legth equal to that of the COEF_CMD structure. That would cause servo to sometimes fail to recogize ew, updated polyomials. All other calls to read the IRIG clock should use the TS_TIME structure defied i irigsmt.h. As soo as getreport() has a ew report from the DSP it does a read to the IRIG device driver to get the Uiversal Time (UT). It stores this i the global variable uttime. (The uits of time are always millisecods.) So, uttime is always the arrival time of the last received report of ay kid. Whe getreport does this call to the IRIG driver, it uses a data legth equal to that of the structure COEF_CMD as described above. If getreport() sees that the "ew" flag i the structure is ozero, it copies the whole irigtimecoef structure to the "commaded" structure. So, ormally, the commaded Page 3 servo.c rev. 1.06

4 structure always cotais a copy of the curret positio polyomials. If it sees that ew is = 2, the it also sets the ewpositio flags i the azspeed ad elspeed structures. This alerts the servo logic i the zeroi() fuctio that a move to a ew object is required, so it should switch from trackig to slewig. Whe servo receives ay ew report from the DSP it uses a large switch statemet (i the mailoop() fuctio) to test the report type code i the first 32-bit word of the report. Each type of commad has its ow case i the switch statemet. By far most of the reports received from the DSP are positio reports. Additioally about 20 "time reports" per secod are throw i. The time report is a o-op that just says what UT time the DSP thiks it is. It is used as sort of a software watchdog. If servo sees the positio reports stop comig ad the time reports do t stop, the servo stops the telescope. This ca happe, for istace, if the DSP processor stops gettig timer iterrupts. The DSP s iterrupt clock is derived from the IRIG time iterface, so a failure i that or the cable coectig the 2KHz sigal from the IRIG to the DSP couter/timer ca cause this to happe. Most of the other types of reports that ca come from the DSP are ot set by the DSP uless servo specifically asks for them. For istace, servo will receive a correctios report (describig the ellipse fit parameters) oly if it seds a commad to the DSP askig for oe. (It does ask for them every 10 secods so it ca report if ay of the correctio coefficiets start lookig wrog. See extcorrcheck ad checkcorrectios().) The oly other types of reports that the DSP seds usolicited are referece pulse reports. Those are set wheever a referece pulse is see o ay of the ecoders. The referece pulse is ot actually used to alter the DSP s cycle cout uless the DSP has previously bee "armed" to do so o the ext ref. pulse AND the pulse is see while the telescope is goig i the forward directio. But, regardless of whether the DSP uses the referece pulse evet or ot, or i which directio the telescope is movig, all referece pulse evets are reported to servo by the DSP. The referece pulse report idicates if the cycle couter was actually used or ot. See the sectio below about the reset-ecoder operatio which is the pricipal use of the referece pulse. There are a umber of diagostic reports which ca be set by the DSP code. These are ot used i ormal operatio. While debuggig the DSP code, they were iserted ito the code at various places to see what the DSP was doig. The DIAGNOSTIC4 report, for istace, just seds 4 32-bit umbers to the Liux host, with a timestamp. Whe servo receives a diagostic report, it just prits out its cotets. Except for the timestamp, the cotets of the diagostic reports have o predefied meaig. They are ot used i the ormal operatio of the program. Processig positio reports Whe servo receives a valid positio report, it calls a fuctio called positioservo(). This does all the processig ecessary to decode the positio ad to update the velocity sigals that go out to the Krupp rack to adjust the telescope positio to keep it o track. It closes the loop. It has bee measured takig 23 microsecods to do this, each time it receives a ew positio report from the DSP. Compilig servo with differet optimizatio optios will probably affect the performace. The 23 microsec. figure was obtaied with optimizatio set to level 2. The stadard makefile i tracker/ compiles for the Gu debugger which will probably degrade performace a little. positioservo() will stop the telescope if the positio polyomials that it is usig get to be more tha 60 secods old. They should ormally get updated every 10 secods. If they start flowig agai, the telescope will resume trackig. (If it has to move a large distace to catch up, it probably wo t do so very gracefully, but subsequet motios should be ormal.) Page 4 servo.c rev. 1.06

5 positioservo() also icremets a cout every time it receives a positio report. It outputs bit 5 (=64) of this cout to the Krupp rack as the watchdog sigal. That oscillates at about 1.5 Hz. If this ever stops chagig for as log as 2 secods, the Krupp rack stops the telescope regardless of what the computer is tellig it. The SMT has oly oe Azimuth ecoder, but it has 2 elevatio ecoders. The servo program is dyamically cofigurable to use either or both of the elevatio ecoders. Normally it uses both ad takes as the elevatio positio the average of the readigs from the 2 ecoders. If the differece betwee the 2 ecoders gets to be too large (< 0 or > 55 arcsec.), it outputs a error message ad picks oe of the 2 ecoders to use ad igores the other. The ecoder that it uses is determied by the global variable elevfailsafe. It is set equal to ecoder 1 by default. It ca be chaged to ecoder 0, by editig servo.c ad recompilig. Note that servo refers to the two elevatio ecoders as 0 ad 1. Much of the SMT egieerig documetatio refers to them as 1 ad 2. You ca maually eable or disable the use of either ecoder by usig the el0 ad el1 commads. Each takes a argumet of 0 or 1 to disable or eable the associated ecoder. See appedix 1. positioservo() does a few error checks ad computes the azimuth ad elevatio as a floatig poit umber of arcsecods.. It the calls closeloop(). closeloop() evaluates the curret positio polyomials to calculate the desired azimuth ad elevatio ad a desired speed at the curret UT. These are checked to make sure they are withi rage ad the passed to the zeroi() fuctio. If the system is trackig (i.e., ot acquirig a ew object or positio) zeroi() will just i tur call the voltage() fuctio which hadles trackig. If a ew object has bee selected though, zeroi() takes over ad hadles the slew to the ew positio. Whe the telescope gets to the target positio, zeroi() reverts to it s ormal trackig behavior which is to just call voltage() to have it do the fie trackig. The voltage() fuctio has the logic for the basic servo trackig respose of the system. The expressios ad costats used i voltage() are exactly the same as those used i the origial VAXbased cotrol system for the SMT. voltage() computes the curret poitig error agle by subtractig the curret positio (from the DSP) from the target positio (from the polyomial give the curret UT). The it uses the servo trasfer fuctio to compute the velocity which the telescope should have at the curret time. It the calls commadvelocity() with the desired velocity i arcsec/sec. commadvelocity() coverts that to a equivalet usiged iteger value to be writte to the 16-bit D/A coverters (oe for azimuth ad oe for elevatio). This returs the value to voltage() ad also outputs it to the cotrol system via the 16-bit D/A coverters. Voltage() also ca hadle slewig, but ot very gracefully - it has a tedecy to overshoot a bit. That s why zeroi() ormally itercepts big positio chages before voltage() ever sees them ad hadles them first. Should voltage() ever be called with large positio errors (=may arc miutes or degrees), it will do its best ad get there evetually. Fially, after all that computatio, voltage() checks two global flags for each axis called driverequest ad driveeable. The driverequest flag is set whe the track commad (see appedix 1) is used to commad the program to attempt to drive the telescope i oe or both axes. They flag that the operator is requestig servo to drive the telescope. The driveeable flags are validated by a fuctio called checkeables() which is executed every time ay report is received from the DSP processor. checkeables() examies all of the 48 iput bits coected to parallel ports 2 ad 3. These cotai sigals from the Krupp rack which idicate usafe coditios ad system status, ad also whether the Krupp rack is acceptig computer cotrol commads. If these status bits idicate all is well, Page 5 servo.c rev. 1.06

6 checkeables() sets the driveeable flag for oe or both ecoders. If there is ay problem, oe or both driveeable flags will be zeroed. If either of the driveeable ad driverequest flags is zero, the voltage() fuctio the forces the desired velocity sigal to 0, ad stops the telescope from movig. (This actually starts a cotrolled deceleratio to 0 velocity which may take several secods if the telescope is movig fast.) So, if, for istace, the elevatio cabi door is opeed, the telescope will stop. However, servo will cotiue to compute the desired positio as a fuctio of time ad cotiue watchig the telescope s actual positio. As soo as the ihibitig coditio goes away - some oe closes the door - it resumes trackig. Sice the positio error will, i geeral, be large by that time, the servo trasfer fuctio will compute a large error correctio sigal. That is, the telescope will attempt to get back o track as quickly as possible by acceleratig the telescope to the proper positio ad the resumig ormal trackig. Each time a ew velocity is computed, the correspodig voltage sigal is compared to the last commaded voltage. The ew commaded voltage is ot allowed to chage by more tha MAX_VOLT16_CHANGE from the last oe. Nomially this is couts of the D/A iterface - eough to accelerate at 0.1 deg/sec/sec. This is fast eough to brig the telescope from max. speed (omially 4000 arcsec/sec) to a stop i a few secods. Ay ad all fuctios that stop or drive the telescope usig this same voltage() fuctio, so all speed chages are subject to this MAX_VOLT16_CHANGE acceleratio/deceleratio limit. Resettig the Ecoders The shaft ecoders are relative ecoders, producig oe full sie/cosie wave output for every 36 arsecods of shaft rotatio. But they also produce a referece pulse sigal as the shaft turs through a particular absolute agle positio. The referece is a sigal that marks a particular sie wave. The elevatio ecoders seem to have oly oe referece pulse at about 23 deg., but the azimuth ecoder has a ref. pulse every 45 deg. of rotatio. Ufortuately, most are ot clea lookig sigle pulses, but multipeaked, wide, ad geerally very irregular. Their irregularity is quite repeatable, though. We have chose to use the referece pulse at 90 degrees azimuth for that axis. Observatios with the telescope have fixed absolute agle values to the sie waves that are marked with the referece pulse. For the 3 ecoders these fiducial positios are: elev. 0: 2295 waves arcsec = arcsec = 22deg. 57 mi. 10sec. elev. 1: 2394 waves arcsec = 23deg. 56mi 28.5 sec. Azimuth: 8903 waves arcsec = 89 deg. 2 mi. 6 sec. So, for example, whe the azimuth ref. pulse is detected, the system ca reset the azimuth wave couter to 8903 plus 18 arsecods. All subsequet agle motio is measured relative to that positio. Of course the ecoder readig is ot exactly the telescope poitig directio. Because of various sources of flexure ad/or axis misaligmet, small correctios still eed to be applied to the ecoder readigs to determie the true telescope positio. The telescope "poitig model" is used to do that. It is determied empirically by poitig the telescope at various kow objects distributed across the sky ad otig the small deviatios betwee the ecoder readigs ad the actual positio o the sky. These deviatios are the least squares fit to a fuctioal form which is chose to represet telescope flexure ad atmospheric refractio. This documet does ot cocer itself with aythig beyod the absolute ecoder readigs, however. Page 6 servo.c rev. 1.06

7 The process of locatig the ecoder referece pulses ad settig the absolute ecoder readig is called "resettig the ecoders." It is doe by movig the telescope to a positio just before the positio of the referece pulse ad movig the telescope forward (towards icreasig agle) slowly util the referece pulse is see by the DSP. The DSP (if it has bee "armed" to do so) sets its cycle couter to the a priori value listed above as soo as it sees the referece pulse. It also seds a referece pulse report to the Liux host. I priciple the positios output by the DSP thereafter are absolute ad accurate to about 1 arsecod (provided the poitig model correctios metioed above are performed). Util the DSP has see the referece pulse (or otherwise bee commaded by servo to set its cycle couters to a specific value), the positio data that it seds to the Liux processor is completely iaccurate. The telescope also has "coarse ecoders" o each axis. These are just electrical potetiometers whose resistace is liearly related to shaft positio, so they ca be used as absolute shaft ecoders, albeit ot very accurate oes. Withi a few secods of startig the first motio of the telescope (as soo as the DSP idicates it s doe a ellipse fit), servo reads the coarse shaft ecoders (via a 12-bit A/D iterface) ad that positio data is set to the DSP so it ca set its cycle couters. These coarse positios are oly accurate to a degree or so. They are sufficiet to be able to positio the telescope to a poit before the referece pulses ad the do the procedure described above to reset the ecoders. Ay time the DSP sees a referece pulse sigal, it reports it to servo which logs it to the Moitor task. A referece pulse report tells which ecoder geerated the pulse, whether the telescope was movig i the positive or egative goig directio o that axis whe the pulse happeed ad whether the referece pulse was used to alter the ecoder s cycle cout. The cycle couter will ot be altered uless servo has previously "armed" the DSP s ref. pulse logic to do so. If it was armed, the logic disarms itself automatically after the cycle couter is chaged, so that a subsequet ref. pulse evet, while it will be reported, will ot chage the cycle couter. The ref. pulse report also shows the value of the cycle couter whe the pulse was sesed regardless of whether it was chaged. After the ecoders have bee reset, the every time the referece pulse is passed i the positive goig directio, it should always prit out the value of the a priori cycle cout listed above. If, after he ecoder is reset, that umber does ot repeat, the somehow the DSP lost cout of the ecoder cycles, or the ecoder it self has malfuctioed. The referece pulse report does t prit the value that the couter is chaged to (if it was chaged), because that is always the same. Resettig the Ecoders Maually The ecoders ca be reset maually or automatically. To do it maually, just sed the servo program a commad to arm the referece pulse logic for each axis. This is doe with the commads "azrefmode" ad "elrefmode". They take o argumets. After these are executed, the ext time the DSP sees the referece pulse whe it is movig i a positive directio (toward icreasig agle), it will reset its cycle couter for the armed axis. It does t matter if the servo program is drivig the telescope whe this happes or if the operator is movig it i maual mode. You ca do this before servo has bee told to start drivig (via the track commad). So, after givig servo the armig commad, maually move the telescope to a positio before the referece pulse fiducial ad slowly drive it forward util it reports seeig the referece pulse. You ca the back up over the ref. pulse ad, without re-armig it, ru the telescope forward over the fiducial agai. Ay time this is doe after the first armed ecouter of the ref. pulse, the ref. pulse report should show the same cycle cout. Page 7 servo.c rev. 1.06

8 Resettig the Ecoders Automatically The automatic ecoder reset operatio uses the servo program to do all ecessary armig ad telescope motio automatically. The telescope must first be movig uder computer cotrol, of course. The ecoders are reset automatically by sedig the servo program the commads "resetaz", "resetel", or "resetboth". Each axis ca be doe separately or both ca be doe simultaeously. It moves the telescope to a positio before the referece pulse, arms the ref. pulse logic, ad the moves it forward at 1/10 slew speed util it sees the referece. It will report the referece pulse wheever it is see. It the automatically backs up over the referece positio ad rus through it twice more without armig it so the observer ca see if the results, that is, the cycle couts are repeatable. Note that sice the SMT has such a large solar avoidace zoe, there may be log periods (hours) whe the poit o the sky which represets the fiducial idexes for both axes is withi the zoe of avoidace. (That s the poit at az=90deg, el=23 deg.) I that case, usig the resetboth commad will drive the telescope too close to the su, so it will reject the commad. Whe this happes, you have to use the resetaz ads resetel commads separately. Move the telescope to a poit above or below the solar avoidace zoe ad execute resetaz. Whe it has fiished that, the move it to a poit left or right of the avoidace zoe ad execute resetel. Hidig from the Su The SMT s 10 meter dish is capable of cocetratig destructive levels of solar eergy o the receiver, the secodary, or its supports if it is poited too close to the su. For this reaso the telescope has always bee operated with a 30 degree solar avoidace zoe. The software will igore a commad to acquire a object that is withi 30 deg. of the su. (That will i fact cause it to pause, so it will require the operator to upause it to get thigs goig agai.) If it should ever fid itself withi the solar avoidace zoe, the software attempts to move the telescope out of it as quickly as possible. The mailoop() fuctio ormally checks for solar proximity every few secods. The software will tolerate a "grazig" icursio ito the solar avoidace zoe uder some circumstaces. If it detects the telescope is less tha oe degree withi the zoe it does t automatically start a hide-from-su operatio. It shriks it s su checkig time period to about 1/10 sec. ad keeps watchig it. If the telescope stays withi the outer 1 degree of the zoe for more tha about 10 sec., the software takes over ad hides from the su. If the icursio ever exceeds 1 degree (i.e., < 29 deg. from the su) it will hide from the su immediately. This behavior is to allow a mior, brief icursio to be tolerated. Whe the software decides to hide from the su, it first computes the locatio that poit which is just outside the solar avoidace zoe which it ca reach the fastest, give its preset positio ad velocity. It the goes to that positio usig the "direct" slew method described below. This is desiged to miimize the time the telescope speds iside the avoidace zoe. Oce it is at this earby safe poit, it computes a more distat safe poit which is 20 or 30 degrees away ad goes to that poit ad stops. Geerally this will be at a umerically lower azimuth tha the su so that the su will the be movig away from the telescope. If oe axis is disabled, the program does the best it ca to get to a safe spot. It is possible i this case for the program to get caught i a "pich poit". For example, if the telescope is very low i elevatio ad the solar avoidace zoe is just above it ad movig lower ad the azimuth axis is disabled, it ca get stuck. It could move above the avoidace zoe i elevatio, but ot without passig through the avoidace zoe just above it. I this case the program looks at how close it would get to the su if it Page 8 servo.c rev. 1.06

9 were to ru up to a high elevatio. If that distace is greater tha 19 degrees (see TOAST_LIMIT i servo.h to chage this), it will go ayway. It requires the azimuth speed to be < 100 arcsec/sec before it will chace this. If the > 19 deg. coditio ca t be met, or the azimuth axis is movig faster tha 100 arcsec/sec, it will move dow to elevatio = 2 deg. ad just keep watchig the situatio. Similar logic is used for the case where the elevatio axis is disabled ad the azimuth is drivable. Su avoidace: Slewig aroud the su There are 2 slew algorithms which the servo program uses to go from the curret positio to a ew positio. If the operator clicks o the "Force Direct" butto i the servo cotrol pael, the "direct" algorithm is used for the ext slew oly. Otherwise it uses a more complex "su avoidace" algorithm which computes a path that is guarateed to keep the telescope at least 30 deg. from the su at all times. If a straight lie path betwee the start ad ed positio does ot ecroach o the su avoidace zoe, that straight lie path is followed. If it does cross the avoidace zoe. the a path that curves aroud the zoe is used istead. The direct algorithm rus the azimuth ad elevatio axes completely idepedetly. It computes the total chage i AZ ad EL eeded to reach the target locatio ad at arrive there at approximately the right target velocity. Each axis is ramped up i speed to the maximum (omially 4000 arcsec/sec, although it ca actually go as fast as 5400 arcsec/sec), held at that maximum for a precalculated period, ad the ramped dow so that it reaches the target value at the desired velocity. If the distace is short eough, it may ot be able to reach termial velocity before havig to start deceleratig. So, a graph of velocity as a fuctio of time for oe axis is either goig to look like a triagle for smaller movemets or a trapezoid for log oes. Movemets greater tha about 11 deg. produce the trapezoidal case. The axis that has the smaller distace to go will fiish slewig first ad start trackig while the other axis is still slewig. There is o coordiatio of movemet betwee the 2 axes. The su avoidace path algorithm computes a list of AZ EL positios, at roughly 1 degree icremets ( 1 deg. o the sky), which defie a path from the start poit to the target. The path is guarateed to always stay at least 30 degrees from the su. First the program tests a "straight" lie i AZ-EL space (which is ot a straight lie o the sky) from the start poit to the fiish poit. It checks this lie at oe degree itervals to see if it stays clear of the su. (Computig the distace to the su is just the dot product of the uit vector to the su ad the uit vector to the poit o the path, so it is computatioally cheap - o trig fuctios ivolved except for the very first poit.) If all poits are far eough from the su, the straight path is used. If the straight lie i AZ_EL space crosses the solar avoidace zoe, it uses a "stretched strig" algorithm to compute a path aroud the su. First the 30 degree radius circle o the celestial sphere cetered o the su is expressed as a list of about 200 AZ-EL poits. I the AZ-EL coordiate system it is a distorted circle. From this poit o, the problem is two dimesioal i AZ-EL space. The path is what you would get if you stretched a strig from the start poit to the ed poit, but deflected it aroud the su avoidace zoe, as though it were a physical barrier. This is accomplished by computig a straight lie from the start poit to a poit taget to a slightly expaded su avoidace zoe ad the other taget lie from the destiatio poit to aother taget poit to the su avoidace zoe. Betwee the 2 taget poits, the (slightly expaded) su avoidace zoe perimeter is take as the path to be followed. By piecig these 3 segmets together, a list of poits from the start to the destiatio is compiled at about 1 degree itervals. Page 9 servo.c rev. 1.06

10 The program the computes times, velocities ad acceleratios for the start of each iterval i the list. The servo loop does its best to keep the telescope o this schedule to get it to the destiatio. It always accelerates alog the arc of the path at 360 arcsec/sec to a maximum of 4000 arcsec/sec. (i oe coordiate - see below). Whe it gets to just the right spot ear the ed of the track it decelerates at 360 arcsec/sec alog the arc so that it eds up at 0 arcsec/sec. at the target. Whe followig a su avoidace path, velocities are chose so that oe of the axes is always beig drive at maximum speed (assumig the path is log eough to allow reachig maximum speed) of 4000 arcsec/sec. As the path curves aroud, that may switch seamlessly from oe axis to the other, but oe of them will always be ruig at 4000 arcsec/sec. If the operator gives servo a ew target positio (or a "halt" commad) before it fiishes the slew path it is o, it computes a ew series of acceleratios ad velocities alog the same path it is followig that will brig it to a halt. This ormally takes about 5 or 6 itervals (5 or 6 degrees). Oce stopped it the computes a ew path to the ew object ad takes off for that ew target. (I the case of a halt commad, it actually back tracks a bit to the positio it had whe the halt commad was give ad stops there.) The cable wrap The SMT ca rotate a total of 540 degrees i azimuth. Azimuth is measured from -90 degrees at due West aroud clockwise to 450 degrees (due East). I reality the program de-rates these limits by 2 degrees, so the usable rage is from -88 to The servo cotrol logic defies the "positive wrap" as the AZ values i the rage 272 to 448 degrees. The "egative wrap" is the AZ values i the rage +88 to -88 degrees. The these regios overlap. So a object at AZ=10 degrees ca also be accessed at AZ = = 370 degrees. The servo logic ormally takes the shortest path whe movig from its preset positio to a ew source. If it is at AZ = 10 deg. ad is commaded to a source at AZ = 355, the shortest path is to go to AZ = -5 deg., so it will move couterclockwise to that positio. However, the operator may wat to force it to wid aroud the log way. You ca force it to use oe wrap or aother by usig the "usewrap" commad. "usewrap" takes oe argumet which is 1, 0 or -1. A 1 tells the program to always use the positive wrap, 0 tells it to go the shortest way (this is the default) ad -1 tells it to use the egative wrap. So, if a object is at AZ = 10 degrees ad you have previously executed "1 usewrap", servo will fid this object to be at 370 because that is i the positive wrap. After you call usewrap, the wrap that you specify remais i force util you specify otherwise by aother call to usewrap. The default is 0, that is to use botyh wraps, whichever is closer. Exceedig the Lower Elevatio Limit The ormal lower elevatio limit is 2.0 deg. (see EL_MIN_LIMIT_DEG_DEFAULT i servo.h). Normally the computer will chose paths that are always above this value. If a object moves below this limit, the telescope will ot follow it, although it cotiues trackig i azimuth. Two degrees is the elevatio at which the "Elev. Pre-limit dow" sigal from the Krupp rack turs o. Whe this happes the Krupp servos automatically limit the elevatio speed to 10% of maximum. If the telescope is to move below the 2.0 deg. limit, the computer has to set its ow Elevatio speed limit to 10% if it is to be able drive the telescope properly i this regio. They both have to use the same rules. Page 10 servo.c rev. 1.06

11 To exceed the 2.0 deg limit the operator has to do 2 thigs. First he has to set a ew miimum elevatio limit. This is doe with the "elmisec" commad. It takes a argumet which is a iteger umber of arcsecods. So, "3600 elmisec" sets it to 1 degree. "0 elmisec" sets it to zero degrees. Next the operator has to set the maximum velocity allowed i this regio. This is doe with the "maxvelsec" commad. Its iteger argumet is i uits of arcsec/sec, so "400 maxvelsec" would set it to the 10% value that the the Krupp rack eforces below the 2.0 degree pre-limit. (Note that this ca also be used to set the velocity limit to values higher tha the 4000 default value. Not recommeded, though.) After both of these steps have bee doe, the program will respod to commads to move to positios with elevatio < 2.0 deg. There is a hard limit at 0 degrees. Below this, the Krupp rack igores the computer s velocity sigal. Whe you are ready to move the telescope back above elevatio 2 degrees, you ca commad it to a positio at or just above 2 degrees (it s ruig at oly 10% of max speed, so do t tell it to go a log way), or just move it maually above 2 degrees ad the use the 2 commads described above to set it back to its ormal coditio. Page 11 servo.c rev. 1.06

12 Appedix 1 servo commads The servo program has a simple commad parser ad looks for text iput from either the keyboard or a socket at ay time. The sytax for the ASCII commads is the same regardless of how they are trasmitted to the program. After each commad is executed, a respose is set back to the user. It starts with the ASCII characters "OK:" or "FAIL:" followed by some text which is peculiar to each commad which cofirms what happeed. May commads ca oly retur the "OK:" respose. See the idividual commads i servo.c to see what is retured as a respose for each commad. Note that most of the commads below are for diagostic use ad wo t make much sese to the telescope operator. All commads are documeted, but oly a small portio of them are useful to the operator. I the lies below showig the call sequece for each commad, the (usually) right most word prited i bold is the commad ame. The words to the left of it (if ay) are the argumets that it takes. They are to be specified as umeric literals. Ay words that may be show after it are umbers the commad leaves o the parameter stack. More tha oe commad ca be placed i oe lie of text. Blaks are delimiters. For example i the example below the commad FOO takes 2 argumets, "a" ad "b" ad leaves a result "c". a b FOO c A example of a fuctio that does this is "+". It takes 2 argumets, adds them ad leaves the result o the stack. so "1 5 +" leaves a 6 o the stack. Hardly ay of the commads leave a result. Note that the ames are case sesitive! abort: Aborts a resetboth, resetaz or resetel commad that is i progress. abort Ay reset ecoder operatio that was started by a resetaz resetel or resetboth commad is immediately aborted by this commad. AZ: specify a particular chael to be oe of the Azimuth sigals group cha sig AZ Assig oe of the azimuth ecoder sigals to a particular chael umber o a particular eight chael A/D. "group" idetifies the A/D board - either 1 or 5 for the oe coected to comport 1 or comport 5. "cha" is the chael umber, 0-7. "sig" is the sigal, SIN, COS or REF. Normally this is ivoked from the servocfg.txt file whe it is loaded to declare the chael assigmet. A example would be "1 0 SIN AZ" which declares the Azimuth ecoder sie sigal to be coected to group oe, chael 0. This chage will ot take effect util sedcha is executed. See EL0, sedcha ad showcha. group group umber = 1 or 5 to idetify the A/D cha chael o that A/D. Always 0-7. sig Sigal idetifier. Must be SIN, COS, or REF. azrefmode: Arm DSP to use the Azimuth referece pulse. azrefmode Page 1 servo.c rev. 1.06

13 This "arms" the azimuth referece pulse logic i the DSP computer. After executig this, the ext time the DSP sees the azimuth ecoder referece pulse whe the telescope is movig i the directio of icreasig azimuth ("positive-goig"), it will reset the azimuth cycle couter to the stadard a priori value for that axis. This ca be u-doe, that is, u-armed, by usig the mode0 commad. That value is fixed i the geeral.h file. See elrefmode. Normally the ecoder cycle cout is reset i a more automatic way by usig the "resetaz" or "resetboth" commads. c: Request a correctio report ad prit it c This takes o argumets. It seds a commad to the DSP that tells it to sed back the curret correctio costats. The report specifies the offsets, amplitude ad phase correctios for all 3 ecoders. Whe ay correctio report is received, the correctio umbers are checked to see that they are reasoable. If they are too far off, servo prits a warig message. co: Force read of coarse ecoders ad set az ad EL cycle couters. co Forces a read of the coarse ecoders ad the does a setcyclectr commad to have the DSP set its cycle couters to the values just read i. This is largely diagostic. It was used at a time whe the coarse ecoder readig was failig ofte due to high oise levels. Note that executig this after a resetecoders operatio will de-iitialize the positio, that is, reduce the positio accuracy to that of the coarse ecoders. It will be ecessary to do aother ecoder reset to do accurate poitig agai. coarse: Sythesize coarse elevatio voltage coarse This is a diagostic fuctio which takes a argumet from 0 to 45. It uses a uused DAC chael to geerate a voltage iput to the A/D chael which ormally carries the coarse elevatio positio. A short jumper cable coects the DAC to the A/D. This allows oe to maually (before executig track ) set a voltage o the coarse elevatio iput correspodig to a agle of 0 to 45 degrees. It ca t do more tha that because the DAC output is +-5v ad the A/D iput is +-10v. This was used to test the coarse ecoder iputs. It also saves some time gettig the test set up to the desired elevatio positio. Number of degrees correspodig to the desired coarse elev. iput. Must be betwee 0 ad 45. COS: pushes a code umber o the stack that idetifies a ecoder cosie sigal. COS COS is a "costat" fuctio. It pushes a sigal code umber o the stack. See SIN ad REF. the code umber for a cossie sigal. dacset: Sed a specified data value to a specified DAC chael. ch d dacset Seds a specified 12-bit data value to oe of the 6 DAC chaels. A data value of 0 produces -5v o the DAC output. A value of 4095 produces +5v o the DAC output. ch The DAC chael umber. Must be betwee 0 ad 5. d The 12-bit data value produces -5v to +5v gives 0v. Page 2 servo.c rev. 1.06

14 dasread: read all 16 chaels of A/D ad prit raw readigs dasread reads all 16 chaels of the 12-bit A/D coverter ad prits out the raw data values. This is a passive operatio. It has o effect o the telescope. dsperrors: prits a summary of DSP errors dsperrors Takes o argumets. This prits oe lie for each possible dsp error code ad a cout of how may times it has received each error message from the DSP. elrefmode: Arm DSP to use the Elevatio referece pulse. elrefmode This is just like azrefmode, except it works for the elevatio ecoders. Affects both ecoders. See azrefmode. EL0: specify a particular chael to be oe of the Elevatio 0 ecoder sigals group cha sig EL0 Assig oe of the elev. 0 ecoder sigals to a particular chael umber o a particular eight chael A/D. "group" idetifies the A/D board - either 1 or 5 for the oe coected to comport 1 or comport 5. "cha" is the chael umber, 0-7. "sig" is the sigal, SIN, COS or REF. Normally this is ivoked from the servocfg.txt file whe it is loaded to declare the chael assigmet. A example would be "5 0 SIN EL0" which declares the elev. 0 ecoder sie sigal to be coected to group five, chael 0. This chage will ot take effect util sedcha is executed. See EL1, sedcha ad showcha. group group umber = 1 or 5 to idetify the A/D cha chael o that A/D. Always 0-7. sig Sigal idetifier. Must be SIN, COS, or REF. el0: Eable or disable the use of elevatio ecoder 0. el0 Takes a flag which idicates if elevatio ecoder 0 should be used or ot. If is 0, elevatio ecoder 0 is igored. If it is ozero, it is used. See el1. Flag idicatig if elevatio ecoder 0 should be used. 0=igore el0. ozero = use el0. EL1: specify a particular chael to be oe of the Elevatio 1 ecoder sigals group cha sig EL1 Assig oe of the elev. 1 ecoder sigals to a particular chael umber o a particular eight chael A/D. "group" idetifies the A/D board - either 1 or 5 for the oe coected to comport 1 or comport 5. "cha" is the chael umber, 0-7. "sig" is the sigal, SIN, COS or REF. Normally this is ivoked from the servocfg.txt file whe it is loaded to declare the chael assigmet. A example would be "5 0 SIN EL1" which declares the elev. 1 ecoder sie sigal to be coected to group five, chael 0. This chage will ot take effect util sedcha is executed. See EL1, sedcha ad showcha. group group umber = 1 or 5 to idetify the A/D cha chael o that A/D. Always 0-7. sig Sigal idetifier. Must be SIN, COS, or REF. Page 3 servo.c rev. 1.06

15 el1: Eable or disable the use of elevatio ecoder 1. el1 Does the same fuctio as el0 except it does it for elevatio ecoder 1. See el0. Flag idicatig if elevatio ecoder 1 should be used. 0=igore el1. ozero = use el1 go: Sed a "go code" to the DSP go This seds a go code to the DSP. Whe the DSP first starts up, the DSP processor hags waitig for the go code before it does aythig else. The DSP always respods to a go code commad with a "iitializatio report". This cotais the DSP s value of UT, the report period it was last commaded to use ad some iformatio o comport 5 which is used for the A/D data. halt: Stop a slew ad reset the slew state variables. halt This commad is also available as the "HALT" butto i the tracker/servo cotrol pael. "halt"assumes the slew path-followig software has gotte cofused, so it does t use it (as susped does). It forces the path-followig state variables ito their iitial coditio ad stops both axes as fast as possible. It the commads the telescope to go to a positio which is equal to the positio it had whe the halt commad was give. If the telescope was sleewig whe halt was executed, this meas it will backtrack a few degrees to get to the halt positio. It will the stay there. It is still trackig, it s just trackig a object that is t movig. So, if you commad it to a ew positio, it should be able to move to it ormally. The real purpose of the halt commad is to re-iitialize the path-followig software. So, if you see it havig trouble executig a slew properly (sometimes it gets hug), use halt. hatches: Move the telescope to the hatches positio hatches This commad is also available as a butto i the "Service Positios" cotrol pael. This moves the telescope to the hatches positio at AZ = 265 degrees. The preferred elevatio for the hatches positio is 88 degrees. (See MAX_ELEV_SLEW_DEG i geeral.h.) However, whe the su is up, the system may be forced to choose a lower elevatio to avoid the su. It will always take a positio above the su if it ca. If it ca t it will choose a positio about 10 degrees ahead of the su. If it has picked a positio that will evetually be ovverru by the su avoidace zoe, it will prit a warig message to that effect. help: Prits the ames of all commads ad summary of their argumets. help Prits out the cotets of the commad list alog with summaries of the argumets each commad takes (if ay). keep: Force mai while loop variable keep Sets the keep variable cotrollig the mai while loop i servo to the value. This is a diagostic commad ad should ot be used durig ormal operatio. The loop rus oly as log as keep == 1. Value to which the keep variable is set. Page 4 servo.c rev. 1.06

16 malog: Make a maual log etry malog <strig> Allows you to eter 1 lie of text ito the servo.log file. If there is a servo related problem you ca type (i the servo xterm widow) the word malog followed by whatever text. It takes all the text after malog up to the carriage retur ad places it i the servo.log file with a time stamp. So it might look like this: malog telescope wot move whe a ew object is selected mode0: Commad DSP to set its mode variable to 0 mode0 The DSP has a mode variable which basically tells it whether it is supposed to sed reports or ot ad if it is armed to use the ext positive goig referece pulse that it ecouters. A value of 0 is the "ormal" value which has it doig reports ad ot armed for referece pulses. This is a maual way of forcig it to have a zero value. It allows oe to udo a "arm" commad. See azrefmode ad elrefmode. report: Chage the DSP s positio report period report Specifies to the DSP processor how frequetly it should sed a positio report. The default is 10 ms. This ca be chaged at ay time. It should t be ay faster tha 6ms. The desired report period i uits of millisecods. pritpos: start/stop pritig positio report pritpos If is ozero, servo begis pritig positio reports every 2 secods. If it is 0 it stops pritig reports. The delay period is cotrolled by PRINT_PERIOD i servo.h. : Logical flag (0 or 1) to idicate if pritig should be started or stopped. readcfg: Reads i the servocfg.txt file. readcfg Looks for a file called servocfg.txt ad loads it. That is, that file cotais executable shell commads. This reads the file ad executes those commads. If the file caot be foud, it looks for a file called servocfg.master ad copies it to servocfg.txt. This file cotais declarative commads that defie the assigmet of ecoder output sigals to A/D iput sigals. rec: To record raw ecoder data cha ecodernum time rec Starts recordig 2 chaels of raw ecoder data from the specified ecoders i files o the liux system. cha 0 meas record sie & cosie. 1 meas record cosie ad ref. pulse ecodernum the logicl OR of 1, 2, ad/or 4. 1 meas to record Azimuth, 2 meas record elevatio ecoder 0 ad 4 meas record elev. ecoder 1. So 7 will record all ecoders. time legth of time that data should be recorded i uits of millisecods. So 1000 = 1 secod. recpos: Record all positio reports for a time period recpos Page 5 servo.c rev. 1.06

17 This commad causes servo to start recordig all positio reports to a disk file startig immediately ad cotiuig for the specified umber of positio reports. The positios are recorded i a ASCII text file called positios.txt. Each lie is oe report. A argumet of 100 would record the ext 100 positio reports. At the omial rate of 100/sec. that would take 1 secod of time. Oe record cosists of 13 colums of iformatio. The fields are: 1- The time from the IRIG clock (i secods) whe the positio report was recieved. 2- The UT that was put ito the positio report by the DSP. This is a iteger umber of millisecods. 3- The Azimuth expressed as a floatig pt. umber of arcseods. 4- Elevatio ecoder 0 expressed as a foatig pt. umber of arcsecods. 5- Elevatio ecoder 1 expressed as a foatig pt. umber of arcsecods. 6- Observed Azimuth speed i arcsecods/sec. i expoetial format. 7- Observed Elevatio 0 ecoder speed i arcsecods/sec. i expoetial format. 8- Observed Elevatio 1 ecoder speed i arcsecods/sec. i expoetial format. 9- Projected (computed) azimuth speed i arcsec/sec. 10- Projected (computed) elevatio speed i arsec/sec. 11- RMS deviatio for AZ ecoder. This is the RMS of 1-(si**2 + cos**2), so it should be < RMS deviatio for Elevatio 0 ecoder. 13- RMS deviatio for Elevatio 1 ecoder. Number of positio reports which are to be recorded to disk. REF: pushes a code umber o the stack that idetifies a ecoder referece pulse sigal. REF REF is a "costat" fuctio. It pushes a sigal code umber o the stack. See COS ad SIN. the code umber for a referece pulse sigal. resetaz: Reset the Azimuth ecoder oly. resetaz This is the same as resetboth except that it resets oly the azimuth ecoder. resetboth: Reset both Azimuth ad Elevatio ecoders. resetboth This commads servo to start a sequece of automatic telescope motios to calibrate, or reset, both azimuth ad elevatio ecoders. It automatically moves both axes (usig the coarse positio ifo) to a couple degrees before the fiducial idex poits. It the arms both azimuth ad elevatio ad rus the telescope forward i both axes util the referece pusle is see. It the backs up over it ad backs up for 10 more secods ad repeats the process twice. After this is doe, the DSP kows the absolute positio of the telescope (assumig it repeated OK). This is cotrolled by state drive logic ad is fairly robust i dealig with problems. It prits out the cycle couters at the time the referece pulses were ecoutered so that the operator ca see if it is repeatable. The resetabort commad will stop a reset ecoder operatioi that is i progress. resetel: Reset the Elevatio ecoder oly. resetel This is the same as resetboth except that it affects oly the elevatio ecoders. Page 6 servo.c rev. 1.06