Multiple copies of the same embedded subfunction in simulink

Hello, I would like to use multiple instances of a line_buffer (from the eml design patterns) in the same function in order to build a muti-channel buffer. This is intended for hdl gen. A sketch of the code is something like (I provided this code as an example but may not work as is):

function out_vect = multichannel_buffer(u_vect,N)
for ch=1:8
  out_vect(ch) = line_buffer(u_vect(ch), N);
end
end
function y = line_buffer(u, N)
persistent buffer ctr;
if isempty(buffer)
buffer = fi(zeros(1,N), numerictype(u), fimath(u));
ctr = uint8(1);
end
y = buffer(ctr);
buffer(ctr) = u;
if ctr == N
ctr = uint8(1);
else
ctr = ctr + 1;
end
end

The problem here is that both persistent variables (buffer and ctr) are the same on all the calls. Is there any way I can write just one line_buffer function and use it multiple times ( in a channel per channel basis), having a separate variable stack (buffer and ctr) for each channel?

Thanks in advance for any clue, Regards A

[Kiran Kintali]

short of using system object for representing the delay, i do not know if there is a best way to model this using persistent variables in MATLAB. thanks.

function out_vect = multichannel_buffer(u_vect,N)

persistent h1 h2 h3 h4 h5 h6 h7 h8

if isempty(h1)

h1 = dsp.Delay(N);

h2 = dsp.Delay(N);

h3 = dsp.Delay(N);

h4 = dsp.Delay(N);

h5 = dsp.Delay(N);

h6 = dsp.Delay(N);

h7 = dsp.Delay(N);

h8 = dsp.Delay(N);

end

out_vect = u_vect; % Initialize

out_vect(1) = step(h1, u_vect(1));

out_vect(2) = step(h2, u_vect(2));

out_vect(3) = step(h3, u_vect(3));

out_vect(4) = step(h4, u_vect(4));

out_vect(5) = step(h5, u_vect(5));

out_vect(6) = step(h6, u_vect(6));

out_vect(7) = step(h7, u_vect(7));

out_vect(8) = step(h8, u_vect(8));

end

Answer 1

[Kaustubha Govind]

It seems writing line_buffer as a class with 'buffer' and 'ctr' as its members might be the right way to solve this problem. However, MATLAB Coder started supporting code generation for MATLAB classes only in R2012a. I believe you need to write the class as a System Object. Also see Code Generation for MATLAB Classes for more information.

[Andres]

Hi Kaustubha,

Thanks for your kindly answer. Unfortunately I don't have access to the R2012. I have seen the System object you have mentioned but seems it can generate only C/C++ code but hdl. Could you please confirm this?

As a workaround I copied the sub-function multiple times but it is not an elegant solution

Thx!

[Kaustubha Govind]

Oops, it does look like only a limited set of shipping System objects are supported for HDL Code Generation: http://www.mathworks.com/help/toolbox/hdlcoder/ug/bs4rkua-2.html#bteb6n_

Sorry, I don't know what might be a better solution at this point. Perhaps you can wait and see if someone else has a better idea or contact Tech Support if you're on maintenance.

Answer 2

[TAB]

One way is to pass the buffer & ctr on each function call and also return their updated values each time. Something like this

function out_vect = multichannel_buffer(u_vect,N)
 buffer = Initialize;
 ctr = Initialize;
 for ch=1:8
  [out_vect(ch) buffer ctr] = line_buffer(u_vect(ch), N, buffer, ctr);
 end
end

This will remove the need of persistent variable. You can manage buffer & ctr variables for your each channel using arrays.