rotate bytes in array

[MikeWinston]

instead of a for/next shift, how about a in-place overwrite. (instead of shifting the data, shift the index variable.)

index = 0

Loop:
adResult = {...new voltage value}

arraySum = arraySum - arr[index]
arr[index] = adResult
arraySum = arraySum + adResult

if index = 29 then
index = 0
else
index = index + 1
endif

goto Loop


Mike -

[Art]

Mike, is the compile size smaller?
I can't really check in my project because it appears code is being fragmented over several pages
after I crossed the first boundary.

Robert, Didn't know you could use a STEP -1 directive,
but if it works, it's shorter, and saves a useless byte.

It appears to be working nicely, but I will shorten it if possible.
It's for my car computer I've posted about here before.
With the vehicle running, the voltage reading is live.
With the engine stopped, but accessories relay on,
the stereo amplifiers tend to cause the voltage to jump around (understandably).
The thirty second average is then displayed and acted on to turn accessories off if the average is too low.

[MikeWinston]

Art,
don't know if it's smaller. i was going for speed rather than code size.

Mike -

[languer]

Adding a new voltage reading every second to calculate a new mean voltage over thirty seconds

I was thinking along the lines of what instead of what Tachyon wrote

a for/next shift, how about a in-place overwrite. (instead of shifting the data, shift the index variable.)

But, perhaps you want to look at rolling averages...
http://www.pbpgroup.com/modules/wfse...hp?articleid=7
http://www.picbasic.co.uk/forum/showthread.php?t=12183
http://www.picbasic.co.uk/forum/showthread.php?t=8046
http://www.picbasic.co.uk/forum/showthread.php?p=41702
http://www.picbasic.co.uk/forum/cont...ith-hysteresis

[LinkMTech]

Guys,
May not be the solution for Art's project, but this post interested me because I was also stumped trying to shift bytes of data FIFO and ended up making something work for me.
I liked the FOR/NEXT approach given here and thought I would try it since it looked faster and smaller since I'm really collecting 32 bytes instead of 12 in this example.

My kludge: This scheme uses 24 words and takes 12.5us

DEFINE OSC 8

RX      VAR BYTE        ' Buffer data
XYZ_val VAR BYTE[12]    ' Accelerometer XYZ data
TC_OUT  VAR PORTC.4     ' Test point to measure loop time

Load_array:
TC_OUT = 1
    XYZ_val[0] = XYZ_val[1]     ' Oldest data
    XYZ_val[1] = XYZ_val[2]
    XYZ_val[2] = XYZ_val[3]
    XYZ_val[3] = XYZ_val[4]
    XYZ_val[4] = XYZ_val[5]
    XYZ_val[5] = XYZ_val[6]
    XYZ_val[6] = XYZ_val[7]
    XYZ_val[7] = XYZ_val[8]
    XYZ_val[8] = XYZ_val[9]
    XYZ_val[9] = XYZ_val[10]
    XYZ_val[10] = XYZ_val[11]
    XYZ_val[11] = RX            ' Newest data
TC_OUT = 0    
RETURN

Was surprised to to find that this scheme uses 43 words and takes 216us:

DEFINE OSC 8

RX      VAR BYTE        ' Buffer data
XYZ_val VAR BYTE[12]    ' Accelerometer XYZ data
TC_OUT  VAR PORTC.4     ' Test point to measure loop time


Load_array:
TC_OUT = 1
    FOR z = 0 to 10
        XYZ_val[Z] = XYZ_val[Z+1]
    NEXT z
    XYZ_val[11] = RX
TC_OUT = 0
   
RETURN

It meant more typing but saved some space and time.

[Demon]

...It meant more typing but saved some space and time.

I'm not surprised at all. We quickly forget that FOR-NEXT commands are a combination of ADDs, IFs and GOTOs in the background. The only problem is that the compiler has to make it generic to work for many circumstances; like the STEP -1 example. So now it has to include SUBTRACTs as well, that generates even more code whether you need it or not.

I'm simplifying, but that's pretty much it.

I use the simplified commands 'cause I haven't run out of space yet, and speed hasn't been an issue yet either. But if I ever reach that point, that's when I start breaking them down to their basic elements.

Robert


EDIT: Assembler class was back in '78-'83 era, yeesh...

[LinkMTech]

Thanks for the insight Robert.
The PBP simplified commands are the very reason I started "programming" especially after seeing the difference Bruce gives on his site.

My PIC16F1823 is nearing the end with 2020 words used and just happened to need the space and faster time. Plus it was just rewarding to figure this out on my own and thought I'd share a little for some other newbie out there.

[Demon]

...Robert, Didn't know you could use a STEP -1 directive,
but if it works, it's shorter, and saves a useless byte...

Yup, got off my lazy butt and got the manual, it's in there.

So far our score in PBP knowledge:
Robert 1 .... Art 56,743