Re: [Iverilog-devel] vpi_put_value

[Martin W. <ic...@ma...>]

Hi Yong,

My apologies. I looked in the test suite for something to adapt to reproduce the problem, found 
that, and didn't read it carefully enough!

If the compiler detects that a system function has constant arguments, it will try to evaluate it at 
compile time, using a built-in implementation. That is why your first call works. We should fix that.

The second call fails because the compiler is using the return type for the built-in implementation 
(real) rather than the return type of the replacement (32 bits). There is supposed to be a method of 
fixing that, by suppling the compiler with a ".sft" file that provides the return types of 
user-defined system functions, but that also appears to be broken in this case. I'll look into that.

Martin


On 14/10/19 08:23, fuyong wrote:
> Hi, Martin,
> 
> Finally figure out the reason. In the original example, the 1999 version I
> have, intention of the test is to override the system defined function,
> such as $pow. In your example, you used $my_pow() instead. Guess that in
> Iverilog, system defined function calls could not be overwritten yet.
> Actually I did noticed in my test with $pow(), the first $pow() called the
> system pre-defined function, the second one goes to user defined function.
> This is why the first $pow() passed, and the second one get error.
> 
> The version I have is:
> version 11.0 (devel) (s20150603-641-ga8318db2)
> 
> Many thanks for the help!
> 
> Yong
> 
> 
> 
> On Sun, Oct 13, 2019 at 2:29 AM Martin Whitaker <
> ic...@ma...> wrote:
> 
>> I can't reproduce the failure. We have that example in the test suite
>> already - see
>>
>>     https://github.com/steveicarus/ivtest/blob/master/vpi/pr1693971.c
>>     https://github.com/steveicarus/ivtest/blob/master/vpi/pr1693971.v
>>
>> Please tell us what version of iverilog you are using, and what changes
>> you
>> have made to the example. Just changing the type of 'result' to 'int' made
>> no difference for me.
>>
>> fuyong wrote:
>>> Hi,
>>>
>>> This is a test in Stuart Sutherland's PLI handbook, and it works well
>> with
>>> commercial tools. In Iverilog, we can have compile done, but run time
>> show:
>>>
>>> $pow(2, 3) returns 8
>>> Unsupported format 6.
>>> vvp: vpi_tasks.cc:179:virtual __vpiHandle*
>>> sysfunc_real::vpi_put_value(p_vpi_value, int): Assertion `0` failed.
>>>
>>> There are two $pow() calls .First one returns correct result, second one
>>> failed. with vpi_print, we find seems like the first pow() did not even
>>> called  our defined function (might be using the $pow in build-in
>> $pow()?).
>>> Any way, "result" is defined as int, not sure why the assertion is
>> trigger
>>> in run time.
>>>
>>>
>>>
>>> === Verilog side:
>>>     initial
>>>       begin
>>>         a = 1;
>>>         b = 0;
>>>         #1 $display("$pow(2,3) returns %d", $pow(2,3));
>>>         #1 result = $pow(a,b);
>>>         #1 $display("$pow(a,b) returns %d (a=%d b=%d)", result, a, b);
>>>
>>> === C side:
>>>
>>>     tf_data.type        = vpiSysFunc;
>>>     tf_data.sysfunctype = vpiSysFuncSized;
>>>     tf_data.tfname      = "$pow";
>>>     tf_data.calltf      = PLIbook_PowCalltf;
>>>     tf_data.compiletf   = PLIbook_PowCompiletf;
>>>     tf_data.sizetf      = PLIbook_PowSizetf;
>>>     vpi_register_systf(&tf_data);
>>>
>>>
>>> int PLIbook_PowCalltf(char *user_data)
>>> {
>>>     s_vpi_value value_s;
>>>     vpiHandle   systf_handle, arg_itr, arg_handle;
>>>     int         base, exp, result;
>>>
>>>     systf_handle = vpi_handle(vpiSysTfCall, NULL);
>>>     arg_itr = vpi_iterate(vpiArgument, systf_handle);
>>>     if (arg_itr == NULL) {
>>>       vpi_printf("ERROR: $pow failed to obtain systf arg handles\n");
>>>       return(0);
>>>     }
>>>
>>>     /* read base from systf arg 1 (compiletf has already verified) */
>>>     arg_handle = vpi_scan(arg_itr);
>>>     value_s.format = vpiIntVal;
>>>     vpi_get_value(arg_handle, &value_s);
>>>     base = value_s.value.integer;
>>>
>>>     /* read exponent from systf arg 2 (compiletf has already verified) */
>>>     arg_handle = vpi_scan(arg_itr);
>>>     vpi_free_object(arg_itr); /* not calling scan until returns null */
>>>     vpi_get_value(arg_handle, &value_s);
>>>     exp = value_s.value.integer;
>>>
>>>     /* calculate result of base to power of exponent */
>>>     result = (int)pow( (double)base, (double)exp );
>>>
>>>     /* write result to simulation as return value $pow */
>>>     value_s.value.integer = result;
>>>     vpi_put_value(systf_handle, &value_s, NULL, vpiNoDelay);
>>>     return(0);
>>> }
>>>
>>>
>>>
>>>
>>>
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>>
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