problem with value 'X' in VHDL - Page 2

Altera_Forum · ‎02-09-2011

Dear my best friends

I used vhdl to calculate SVPWM algorithm. I used LPM library for divider. I'd already initial value for all of signal, but It still has "X" value.

This is LPM library

m0 : lpm_divide----------divide component
GENERIC MAP (LPM_WIDTHN=>32, LPM_WIDTHD =>32, LPM_PIPELINE=>1,LPM_NREPRESENTATION =>"SIGNED", LPM_DREPRESENTATION =>"SIGNED")
port map (numer=>A,denom=>B,clock=>clk_120n,quotient=>sat);

these are initial value:

signal TTA,TTB,T_sum	: STD_LOGIC_VECTOR(31 downto 0):=(others =>'0');
signal A,B,sat			: STD_LOGIC_VECTOR(31 downto 0):=(others =>'0');
signal T1,T2			: STD_LOGIC_VECTOR(15 downto 0):=(others =>'0');
signal TAA,TBB          : STD_LOGIC_VECTOR(15 downto 0):=(others =>'0');

these are my code:

if clk_120n'event and clk_120n='1' then
	CNT<=CNT+1;
if CNT=x"00" then 
	SECT  <= not (Vref3(11) & Vref2(11) & Vref1(11) );
elsif CNT=x"01" then
	TX<=Vref1;
	TY<=-Vref2;
	TZ<=-Vref3;
ELSIF CNT=x"02" THEN
case SECT is
when "011" =>    
	T1  <=  -TZ;
	T2  <=  TX;
when "001" =>    
	T1  <=  TZ;
	T2  <=  TY;
when others =>
	T1  <=  T1;  
	T2  <=  T2;  
end case;
elsif CNT=x"03" then
	T_sum <=x"0000"& (T1+T2); 
	if T_sum>= x"410" then --X"410"      
		TTA <=T1*x"0410";
		TTB <=T2*x"0410";
	else
		TAA <=T1;
		TBB <=T2;
	end if;
elsif CNT=x"04" then 
	if T_sum>=x"410" then        
		A <=TTA;
		B <=T_sum;
	end if;   
elsif CNT=x"05" then
	if T_sum>=x"410" then 
		TAA <= sat(15 downto 0);
	end if;   
elsif CNT=x"06" then
	if T_sum>=x"410" then 
		A <=TTB;
		B <=T_sum;
	end if;   
elsif CNT=x"07" then
	if T_sum>=x"410" then 
		TBB <= sat (15 downto 0);
	end if;   
elsif CNT=x"08" then
	TAM  <= x"410" -TAA -TBB;    
elsif CNT=x"09" then
	TAO  <= '0' & TAM(15 downto 1);  
elsif CNT=x"0A" then
	TBO  <= TAO + TAA;
elsif CNT=x"0B" then
	TCO  <= TBO + TBB;        
end if;
end if;

The value get "X" value is SAT (result of divider command). I attached the waveforms in this message. I spent a lot of time for it but I still had not found the error.

Please could you help me?

Thank you very much.

Altera_Forum · ‎02-11-2011

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The code you have posted has nothing to do with mine.

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It's mean that, What is difference between:

1. Use add, sub, multiply, divide command directly in code

2. Use lpm library.

Altera_Forum · ‎02-11-2011

The synthesisor will place add/dub/multiply for you, from the LPM library if you write things like

c <= a + b;

c <= a * b;

etc.

And it will probably do a better job at minimising the logic.

The only area where you really have to be careful is dividers because you cannot control the internal pipelining very easily without using the lpm_divide megafunction.

Altera_Forum · ‎02-13-2011

I think your professor just wants you to use structural description for now, instead of designing it using behavioural code (c<=a*b). Probably he just wants you to have a deeper understanding of how you should connect multipliers, dividers, adders, subtractors, etc. in your design, rather than just describing everything behaviourally.

However, in the industry, it is always easier to do a behavioural description.