Building a memory with m-file

Hello,

I have a little problem with my model when I try to create an intelligent memory to my application. The model is shown below:

The Matlab-function block called "Memory Backup" gets data packets into its port "last_data". The data is delayed with one data step, but don´t worry about it. How the Matlab function should work, is told below:

If there are packet losses (boolean 1 (=losses) or 0 (=no losses)), the Memory backup function starts to feed out the last correct data (last last_data -signal during "no losses" time) that was occured before the losses started to appear.

When the packet losses disappear (packet_loss = 0), then the Memory backup -function just feeds through the input data (last_data -signal).

What is inside the Memory backup file, is shown below:

In order to get the Memory backup- function to work, I should find a way where to declare the variable "keep_old_output". I can´t assign it to a 0 or 1 at the beginning of the script because it would affect to the functionality of the script everytime when the script would be run.

Where should I declare it without disturbing the functionality of the script?

Thank you for any kind of help!

Answer 1

[Rajiv Ghosh-Roy]

You need to declare these variables as "persistent". You can check isempty of these variables for initialization.

function y = fcn(packet_loss, last_data)
  persistent keep_old_data
  persistent another_persistent
  % Initialize
  if isempty(keep_old_data)
    keep_old_data = false;
    another_persistent = uint32(23);
  end
end

[Ion]

Thank you!

Indeed the keyword here was the 'persistent' that solved the problem.