4-bit switch

Earl Foster · 2009-03-27 15:58

I am using a 4-bit switch·to adjust timing.· The below procedure is called with each loop of the program and it works without any problems but I wonder if there was a better way of programming it.· A more efficient way.· It is pretty straightforward with only 4 bits but if I need a 5-bit or 6-bit switch the code starts to get pretty long and would be easy to mess up the binary count.

Trying to get better at coding so I was just wondering.

Pub Get_Timing
   case ina[noparse][[/noparse]21..24]
      %0000: maxtime:= 30
      %0001: maxtime := interval * 1
      %0010: maxtime := interval * 2
      %0011: maxtime := interval * 3
      %0100: maxtime := interval * 4
      %0101: maxtime := interval * 5
      %0110: maxtime := interval * 6
      %0111: maxtime := interval * 7
      %1000: maxtime := interval * 8
      %1001: maxtime := interval * 9
      %1010: maxtime := interval * 10
      %1011: maxtime := interval * 11
      %1100: maxtime := interval * 12
      %1101: maxtime := interval * 13
      %1110: maxtime := interval * 14
      %1111: maxtime := interval * 15

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Beau Schwabe · 2009-03-27 16:05

Earl Foster,

How about something like this?

Pub Get_Timing|temp
    temp := ina[noparse][[/noparse]21..24]
    if temp <> 0
       maxtime := interval * temp
    else
       maxtime := 30

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Earl Foster · 2009-03-27 16:52

Serious improvement over my code. I did not realize you could assign inputs in that fashion. Thanks

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"Don't ask yourself what the world needs - ask yourself what makes you come alive, and then go do it." - H.T.Whitman

Phil Pilgrim (PhiPi) · 2009-03-27 16:55

Or (assuming interval > 30):

maxtime := (ina[noparse][[/noparse]21..24] * interval) #> 30

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 3/27/2009 7:16:46 PM GMT

Brian Fairchild · 2009-03-27 17:55

Depending on your definition of 'efficiency' you might want to look at losing the '*' in all the above. Since the prop doesn't have hardware multiplication you'll suffer a performance hit using it. If your routine only runs once at power up then it won't be an issue; if it runs often you may want to speed it up.

I'll happily admit to still learning SPIN but something like this may well be faster...

    maxtime := 0

    if ina[noparse][[/noparse]21..24] == 0
      maxtime := 30 
    if ina[noparse][[/noparse]21] == 1
        maxtime := interval
    if ina[noparse][[/noparse]22] == 1
        maxtime := maxtime + interval << 1
    if ina[noparse][[/noparse]23] == 1
        maxtime := maxtime + interval << 2
    if ina[noparse][[/noparse]24] == 1
        maxtime := maxtime + interval << 3

Phil Pilgrim (PhiPi) · 2009-03-27 18:19

Even in Spin, which is interpreted, multiplications are done in assembly code and add minimal overhead compared with trying to circumvent them in Spin.

-Phil

Beau Schwabe · 2009-03-27 18:50

... And the winner is.... Phil with a Spin·execution speed of 25.4 micro seconds.

See attached timing code.

Original code - 38.2us
Beau's Code· - 35.6us
Phil's Code··· -·25.4us
Brian's Code· -·78.0us

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Earl Foster · 2009-03-27 19:44

I would have to say Phil won too for speed but it did changed the way the procedure works.· So Beau wins!

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"Don't ask yourself what the world needs - ask yourself what makes you come alive, and then go do it." - H.T.Whitman

Post Edited (Earl Foster) : 3/27/2009 8:00:29 PM GMT

4-bit switch

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