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21615 Discussions

What do these warning mean?(VHDL)

Altera_Forum
Honored Contributor II
‎12-09-2009 02:17 AM
1,725 Views

Warning: Synthesized away the following node(s): 

Warning: Synthesized away the following LCELL buffer node(s): 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le3a[17]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le5a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le5a[12]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le3a[17]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le5a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le5a[12]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le3a[17]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le5a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le5a[12]" 

Warning: Synthesized away the following node(s): 

Warning: Synthesized away the following LCELL buffer node(s): 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le3a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le4a[17]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le4a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le4a[15]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le4a[14]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le5a[15]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le5a[14]" 

Warning (14320): Synthesized away node "lpm_mult:Mult2|mult_v6t:auto_generated|le5a[13]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le3a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le4a[17]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le4a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le4a[15]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le4a[14]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le5a[15]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le5a[14]" 

Warning (14320): Synthesized away node "lpm_mult:Mult1|mult_v6t:auto_generated|le5a[13]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le3a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le4a[17]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le4a[16]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le4a[15]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le4a[14]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le5a[15]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le5a[14]" 

Warning (14320): Synthesized away node "lpm_mult:Mult0|mult_v6t:auto_generated|le5a[13]" 

 

Do they affect the behaviour? What should I do next?
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5 Replies
Altera_Forum
Honored Contributor II
‎12-09-2009 05:57 AM
1,005 Views

Depends on the design, if skipping of bits is intentional or not. If you e.g. cut LSB in a fixed point multiply or a similar operation, it would be intentional.

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Altera_Forum
Honored Contributor II
‎12-10-2009 06:42 AM
1,005 Views

Hi,FvM! 

Sorry,I can't follow your thoughts. What do you mean by the example "cut LSB in a fixed point multiply"? 

It seems that these dismissed intermediate signals all used to mutilply computing.In my code,I used the multiply operation in deed. I am wondering that what these lpm_mults come from and why they are synthesized away.Thanks all.
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Altera_Forum
Honored Contributor II
‎12-10-2009 07:32 AM
1,005 Views

I suggest to reproduce your arithmetic by pencil and paper method and check, if all bits are preserved in the final output of your design. In my signal processing designs, I'm cutting bits everywhere.

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Altera_Forum
Honored Contributor II
‎12-10-2009 11:05 AM
1,005 Views

Hi,FvM! 

So your mean is quartus ii may cut bits it think is not neccesary when dealing with multiply operation? And the result maybe wrong? If so,why the software remind us the result maybe wrong? Your suggestion is to check whether it is right, I think that's fussy.THanks a lot,need your reply
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Altera_Forum
Honored Contributor II
‎12-10-2009 11:12 AM
1,005 Views

No, I mean that Quartus most likely reports bits, that have been discarded intentionally, by design. E.g. you have an 16x16 multiply. According to your number format, you scale the result to 16 bit, apply saturation logic to the 8 upper and cut 8 lower bits. The latter causes a warning.

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