You might find that the compiler will convert:

temp_array1[0] = array1[0];
temp_array2[0] = array2[0];
....
temp_array1[15] = array1[15];
temp_array2[15] = array2[15];

directly into 32 MOVFF instructions.

To get this to happen, you will probably  have to make temp_arrayX global or
static.

Bob Ammerman
RAm Systems



----- Original Message -----
From: "Bruce Partridge" <bgpartri@CA.INTER.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, December 21, 2003 4:23 PM
Subject: Re: [PIC:]Two low priority long tasks with several high priority
short tasks.


> This is the code I timed:
>  for (i=0; i<16; i++)
>     {
>        temp_array1[i] = array1[i];
>        temp_array2[i] = array2[i];
>     }
>
> All of the arrays are 32 bit float.
>
> I was quite surprised that it took so long.  The above C code generates
> about 70 instructions in assembler.  With a 1 Mhz instruction clock, the
> processor should execute about 15,000 instructions in 66 ms.  Even going
> through the loop 16 time shouldn't produce anywhere near that number of
> instructions.
>
> I am starting to think that I could write an inline assembler routine that
> would just move the contents without all the array addressing and stuff.
On
> an 18F4552, I should be able to expect the array contents to be
contiguous.
>
> Bruce Partridge
> http://www.rebreather.ca
>
> > It can't take 66ms just to *COPY* the arrays. You must be
> > doing something else also. Couldn't you just clear GIE during
> > the actual *copying* of the data, then re-enable GIE and go on
> > doing that other stuff that probably takes the most part of the
> > 66 ms, I guess. Just copying would at most be a number of MOVFF
> > instructions, and at 4Mhz take the double number of microseconds
> > (plus the GIE handling stuff).
> >
> > Jan-Erik.
> >
>
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