From novak Fri Jul 10 13:04:02 1998 To: cdd@socrates.patnet.caltech.edu Subject: Re: Yerk Darren, Thanks for your reply and offer to help get Vax code. I have a few 'general' questions about the nature of the communications between Yerk and Vax programs. (1) 'Polling' vs. 'ask and wait': Concerning the interaction that takes place when the Mac requests a telescope move: Does the Mac send a command and then keep 'polling' the Vax until it gets there, or does the Mac 'move' command get followed by a period of time during which the Mac waits for the Vax to send a command back saying "I've arrived". Bob L. says the KAO code worked in the "polling" method, but I don't know if Steve (or you?) changed this to conform to CSO scheme. (2) Mac 'always' initiates an interaction between Mac and VAX. ...right? You said that it is the Vax that is listening for commands to move. Is there ever an unsolicited communication sent from the Vax to the Mac (i.e. "ERROR: I'm no longer pointed at the source") ? Or would any such error only be reported to the Mac when the next command from the Mac arrives? (3) No 'checking', right? Does the Mac ever 'check' to see that the telescope is still on target? Or does it just assume that once the telescope has successfully completed the move (and reports this to the Mac) then it will successfully remain pointed at that postion until commanded to move again ? Bob said that the KAO program did no checking. It did not learn about any loss of track that occured during an integration unitl the end of the integration when it attempted to move again and did not meet with success. (4) Vax does absolute moves, Mac does relative moves. ...right? My recollection is that the command to move to a new source was entered into the VAX. But the Mac issues the commands to move to 'right beam' and 'left beam', and also to update the pointing corrections. Is this the general idea: you input into the Vax the target coordinates and then the Mac tells the Vax to modify the 'offsets' to these coordinates? If this is correct then I assume that the only way the Mac knows what source we are looking at (i.e. what exact coordinates) is that it requests that information at the beginning of a file and puts it in the header. Is this correct? (5) Does the beamswitch command look like this: 'right beam now' or like this: 'go over to az-offset 789.2 arcsec' Thanks again for your willingness to help me out. Giles From cdd@socrates.patnet.caltech.edu Fri Jul 10 17:08:27 1998 To: novak@clark.phys.nwu.edu Subject: Re: Yerk Giles, Your guesses are mostly correct: (1) 'Polling' vs. 'ask and wait': Polling is what we do at the CSO. All commands to the telescope receive in principle an immediate response. To check that the telescope is acquired, a separate command is sent (repeatedly -- hence polling). (2) Mac 'always' initiates an interaction between Mac and VAX. ...right? Yes. For Hertz, there is a not an error connection initiated by the VAX. SHARC does have such a connection, though. For active observing at the CSO, we don't really need the errors sent to the Mac since they pop up on the VAX display, but for something like your remote observing at the Pole, that might be a good idea. Either in the form of frequent error status requests from the Mac to the Telescope, or a link where the Telescope sends error signals to the Mac unsolicited. (3) No 'checking', right? Not a lot of checking. I think the only way data acquisition would stop at the CSO is a lost TCP/IP connection, telescope never entering acquired state, or a garbage response to a TCP command. (4) Vax does absolute moves, Mac does relative moves. ...right? Maybe I wouldn't divide it that way, but the positioning of the telescope is done half by the VAX and half by the Mac. Do to pre-existing capability, poiting at sources in a catalog, precession, focusing, and the possibility of some fixed offsets (like RA offset) are done by the VAX. Things specific to Hertz are done on the Mac, like beam switching and figuring out pointing corrections for different pixels and different instrument rotations. All of the positioning commands are absolute (although they may be offset commands). For example, we say "Change the azimuth offset to +200 arcsec" and not "Change the aximuth offset by an additional 10 arcsec". (5) Does the beamswitch command look like this: 'right beam now' or like this: 'go over to az-offset 789.2 arcsec' The command is 'go over to az-offset 789.2 arcsec' Darren