On Sunday 15 July 2012 10:32:13 andy pugh did opine: > On 15 July 2012 14:45, Gene Heskett <ghesk...@wdtv.com> wrote: > > But the internal calculations for velocity etc are done at the servo > > threads granularity of nominally 1 millisecond. So there is no chance > > of the figures being accurate when the count may be up to a > > millisecond old. > > The counts shouldn't be more than a thread-dither old (10uS or so). > The calculation function reads the latest count from the base thread > functions (possibly a base-thread old). > But does it timestamp that data marking the last time it changed? Thinking further about the quadrature thing, it would seem to be a Good Thing if it carried a 4 element time stamp in a rotating buffer so that the time stamps could be added as ints and right shifted 2 places in order to get the average velocity per count over a 4 count cycle. Even that seems to me it would be one heck of a noise filter for any mechanical errors by averaging the 2% or so errors over a full slot. The definition of slot being completely arbitrary as long as its 4 consecutive edges.
How that would work in the face of a direction reversal might make an interesting problem. I do believe its solvable though. By keeping a 4 element array of time stamps, with the address of the element in the array being derived by the A/B since the 2 bits of data would make the last 2 bits of the address into the array, it could then be updated every base thread by writing that timestamp to the AB address of the array, no time consuming conditionals needed. That way the average speed and instant direction could be determined in the FP servo thread using the granularity of the base thread. The servo thread math could determine the direction by looking at the time stamps (find the newest one, then which side is the next newest one on is direction) since the order will change with the direction. > The FPGA in the Pico card being discussed here ought to make an even > better job at being up-to-date. How hard is it to use this pico card with the d525mw boards? They are shall we say, slot starved. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! "A mind is a terrible thing to have leaking out your ears." -- The League of Sadistic Telepaths ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
