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Altera_Forum's avatar
Altera_Forum
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13 years ago

No paths found for timing analysis

When I compile the following code, the compilation proceeds successfully, but the classic timing analyser of quartus generates the warning "Warning: No paths found for timing analysis". The RTL view...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
13 years ago

I have conducted a few more experiments just to be sure that the problem is in the tool. Indeed, the tool calculates a worst-case tpd following some formula that takes tpd of every operation involved in calculations, e.g., tpd=(n-1)*(tpd,or+tpd,and) or the like.

For instance, if I try the following code:

PROCESS (Input_I,Read_Write) IS

BEGIN

Read:

IF (Read_Write = '0')

THEN

Read_Write <= '1';

END IF;

Result:

IF (Read_Write = '1')

THEN

Read_Write <= '0';

Result1_O <= not Input_I;

END IF;

the tool cannot process it because there is no information about tpd of bitwise not operation in a process. Since the subtraction operation is performed as an addition of two's complement (a-b=a+not(b)), the tool cannot calculate tpd for this expression. Furthermore, it does not depend on a device family as I have tried different ones and have got the same result. However, the tool works fine for other operations logical, arithmetical etc.