Regarding a signal being trimmed

[akanksha112]

Hi All,



I have an 8 bit local signal which is used for some internal logic. Now the problem I am facing is when I am debugging using chipscope in the netlist signals , the 5th bit of the signal is trimmed and there is no warning or info regarding this.



I am sharing with you the pice of code related to this . I would be grateful if anyone of you could tell me any hint as to why this could happen. Earlier it was not giving any problem. It is a critical signal and I need to probe on it for my design so cant let go off it .



Here is the part of the code , THE SIGNAL IN QUESTION IS O_BYTE

PROCESS(CLOCK,RESET)

BEGIN

IF CLOCK'EVENT AND CLOCK = '1' THEN

IF RESET = '1' THEN

F_E <= '0' AFTER 1 NS;

F_D <= '0' AFTER 1 NS;

ELSIF ((B_SIZE = TRANS_LEN) OR (FLAG_S = '1')) THEN

F_E <= '0' AFTER 1 NS;

ELSIF ((B_SIZE_2 = TRANS_LEN) OR (FLAG_S = '1')) THEN

F_D <= '0' AFTER 1 NS;

ELSIF ((O_BYTE = X"0A") OR (O_BYTE = X"2A"))THEN

F_E <= '1' AFTER 1 NS;

ELSIF ((O_BYTE = X"28") OR (O_BYTE = X"08"))THEN

F_D <= '1' AFTER 1 NS;

END IF;

END IF;

END PROCESS;

 

[TrickyDicky]

first of all, you realise that "after" values are ignored for synthesis?

secondly, its been removed because of reduction rules. basically what you are askin is:

if o_byte(5) = '1' or o_byte(5) = '0' then
--do something

this is always true, therefore bit 5 wont be checked, and hence removed,