Charles Turner

I noticed the following. If I have a 2-input, 1-output MSP external, 

and I access the vector array inside the DSP loop like so:

Everything is fine. But if I access the second input out of order like 

tmp seems to never take the values of the second input signal, it's 

Anyone else noticed this, or am I crazy/mistaken? Can anyone amplify on 

I noticed the following. If I have a 2-input, 1-output MSP external, 
and I access the vector array inside the DSP loop like so:

   buf[r_indx] = *++in1;
   tmp = *++in2;
   [...]
   *++out = buf[w_indx];

Everything is fine. But if I access the second input out of order like 
so:

   buf[r_indx] = *++in1;
   [...]
   *++out = buf[w_indx];
   tmp = *++in2;

tmp seems to never take the values of the second input signal, it's 
always zero.

Anyone else noticed this, or am I crazy/mistaken? Can anyone amplify on 
the situation?

order-of-access-to-dsp-signals-important

On 2008 Aug 13, at 7:23 AM, Charles Turner wrote:

> I noticed the following. If I have a 2-input, 1-output MSP external,

> and I access the vector array inside the DSP loop like so:

> Everything is fine. But if I access the second input out of order like

> tmp seems to never take the values of the second input signal, it's

> Anyone else noticed this, or am I crazy/mistaken? Can anyone amplify 

There is an optimization in MSP to share and re-use signal vectors, 

and it sounds like this is causing your trouble. Try setting the 

Z_NO_INPLACE flag to turn the optimization off. Something like this 

> Hey all-
>
> I noticed the following. If I have a 2-input, 1-output MSP external,
> and I access the vector array inside the DSP loop like so:
>
>   buf[r_indx] = *++in1;
>   tmp = *++in2;
>   [...]
>   *++out = buf[w_indx];
>
> Everything is fine. But if I access the second input out of order like
> so:
>
>   buf[r_indx] = *++in1;
>   [...]
>   *++out = buf[w_indx];
>   tmp = *++in2;
>
> tmp seems to never take the values of the second input signal, it's
> always zero.
>
> Anyone else noticed this, or am I crazy/mistaken? Can anyone amplify  
> on
> the situation?

There is an optimization in MSP to share and re-use signal vectors,  
and it sounds like this is causing your trouble.  Try setting the  
Z_NO_INPLACE flag to turn the optimization off.  Something like this  
in your new method:
	x->x_ob.z_misc = Z_NO_INPLACE;

On Wed, 13 Aug 2008 08:50:42 -0500, Timothy Place wrote:

> There is an optimization in MSP to share and re-use signal vectors, 

> and it sounds like this is causing your trouble. Try setting the 

> Z_NO_INPLACE flag to turn the optimization off. Something like this 

Thanks for the info, Tim. The order isn't critical for me, so it was 

easily addressed. Did a few hours of head scratching before I figured 

On Wed, 13 Aug 2008 08:50:42 -0500, Timothy Place wrote:
> There is an optimization in MSP to share and re-use signal vectors, 
> and it sounds like this is causing your trouble.  Try setting the 
> Z_NO_INPLACE flag to turn the optimization off.  Something like this 
> in your new method:
> 	x->x_ob.z_misc = Z_NO_INPLACE;

Thanks for the info, Tim. The order isn't critical for me, so it was 
easily addressed. Did a few hours of head scratching before I figured 
out what I was doing wrong, though!

Order of access to DSP signals important?