gEDA-user: BUGS: iverilog reals

[lingwitt at bellsouth.net]

Hello again,

I've been playing around with $realtobits and $bitstoreal,
and I've found things aren't as clean as I'd hoped.

Basically, I want to simulate floating point operations in my modules.
I figured the process would be:
	(1) Convert a real to bits and pass those as an input to a module.
	(2) Convert the input to a real (without needing a variable).
	(3) Perform an operation.
	(3) Convert result of the operation to bits and output.

Here are some problems I've found.

///////////// [ 1 ] /////////////

The following compiles
(and probably shouldn't, unfortunately):

     module reals;
         wire [63:0] blah = $realtobits(6.35e25);
     endmodule

but when run produces:

     ./a.out:7: syntax error


///////////// [ 2 ] /////////////

The following compiles:

     module reals;

         SomeModule someModule
         (
             $realtobits(3.14+3.15)
         );

     endmodule

     module SomeModule
     (
         input  [63:0] in
     );

     endmodule

but when run produces:

     internal error: 13vvp_arith_sum: recv_real(3.140000) not  
implemented
     ../../src/vvp/vvp_net.cc:1386: failed assertion `0'
     Abort trap

Seems like the parse tree is a bit out of whack.
Since this doesn't work, neither does something like this:

     $realtobits($bitstoreal(arg1)+$bitstoreal(arg2))



///////////// [ 3 ] /////////////

There was some problem with realtobits/bitstoreal that
was fixed with the following change:

Index: vvp/vpi_tasks.cc
===================================================================
RCS file: /home/demon/anoncvs/verilog/vvp/vpi_tasks.cc,v
retrieving revision 1.35
diff -u -r1.35 vpi_tasks.cc
--- vvp/vpi_tasks.cc    12 Apr 2007 04:45:53 -0000      1.35
+++ vvp/vpi_tasks.cc    28 Apr 2007 03:25:34 -0000
@@ -577,7 +577,7 @@
        vpip_cur_task = (struct __vpiSysTaskCall*)ref;
        if (vpip_cur_task->defn->info.calltf) {
-           assert(vpi_mode_flag == VPI_MODE_NONE);
+           /*assert(vpi_mode_flag == VPI_MODE_NONE);*/
             vpi_mode_flag = VPI_MODE_CALLTF;
             vpip_cur_task->defn->info.calltf(vpip_cur_task->defn- 
 >info.user_data);
             vpi_mode_flag = VPI_MODE_NONE;