Re: [Iverilog-devel] VVP Performance boots

[Stephen W. <st...@ic...>]

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Cary R. wrote:
| --- On Mon, 4/21/08, Stephen Williams <st...@ic...> wrote:
|
|> WRT xnor_test: Can you instrument the of_XNOR function in
|> vthread.cc
|> and try it? Something like this:
|>
|> 	    vvp_bit4_t lb = thr_get_bit(thr, idx1);
|> 	    vvp_bit4_t rb = thr_get_bit(thr, idx2);
|> 	    cerr << "XXXX XNOR: lb=" << lb
|> << " rb=" << rb
|> 		 << " lb^rb=" << (lb ^ rb) <<
|> " ~(lb^rb)=" << ~(lb ^ rb)
|> ~                 << endl;
|>
|> ... inside the "for" loop of the of_XNOR
|> function. None of the
|> bits in the result should turn into X or Z. If the %xnor
|> instruction
|> generates X results, then the loop in xnor_test.v may go
|> infinite.
|
| The part of the test that is going into an infinite loop is the
"different sized operands (equality)" section.
|
| The small1 value is set to zero initial then increments to one, but
never goes past that. It appears that the sixteen bit xnor value is
calculated correctly. Both the vthread code and a straight print of
large2 shows all bits are set to one.

I think we are looking for some sort of uninitialized memory problem.
It appears that the %xnor opcode is fine in your case, but there is
some problem managing the index variable. Try putting a test print
in the of_ADDI function to look at the first word of the lva array
that is returned by the vector_to_array before and after the "for"
loop that does the addition. At the very least, this will confirm
that the index variable value is stuck.

Perhaps the %set/v or %load/v (if not the %addi) are not working
properly? Seeing what's going into/out of the %addi may help us pin
it down.

- --
Steve Williams                "The woods are lovely, dark and deep.
steve at icarus.com           But I have promises to keep,
http://www.icarus.com         and lines to code before I sleep,
http://www.picturel.com       And lines to code before I sleep."
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