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how to read this code

how to read this code

how to read this code

I am a beginner in vhdl, struggling with vhdl programming. I am currently reading books and trying to understand code by other authors. i have to understand a code structure like this:


entity declaration

architecture behavioral of entity is

signal declarations:

signal(0) <= '1' when signal_1(0)='0' and signal_2(0)='1' else '0';
signal(1) <= '1' when signal_1(1)='0' and signal_2(1)='1' else '0';
signal(2) <= '1' when signal_1(2)='0' and signal_2(2)='1' else '0';
signal(3) <= '1' when signal_1(3)='0' and signal_2(3)='1' else '0';

inport <=  data_in and not signal;

signal_4(0) <= '1' when signal(0)='0' and signal_2(0)='1' else '0';
signal_4(1) <= '1' when signal(1)='0' and signal_2(1)='1' else '0';
signal_4(2) <= '1' when signal(2)='0' and signal_2(2)='1' else '0';
signal_4(3) <= '1' when signal(3)='0' and signal_2(3)='1' else '0';

inport_1 <= signal or signal_4;

do something here
end  process

end behavioral 

my questions are:

  • how this code will work, for behavioral part all statements execute concurrently, but signal_4 depends on signal so will second when-else would wait for signal computation?
  • how inport would be computed, concurrently or sequentially?
  • are all when else for signal computed simultaneously?
  • if i want to count how many bits of signal are turning to '1' after all 4 bits are computed is the 1's counter after when else for signal is the only way to do it? can i somehow count 1's within the when else?
  • if i want the same number of bits to go high for signal and signal_4, how can i do it?
  • if there are more than one processes in a code will they execute concurrently as well, i understand that process executes seuqentially and is executed when sentivity list signals change?
I appreciate any help.

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