From: Stuart Sutherland (stuart@sutherland.com)
Date: Fri Mar 20 1998 - 15:23:31 PST
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I received the following bug from Summit (Simulation Technologies). The
bug involves both the BNF and PLI. Before we can fix the PLI side, we need
the Behavioral task force to resolve whether "null" ports in a port list
are supposed to be legal. As the example which follows shows, Verilog and
VCS both permit the null ports.
>Date: Mon, 16 Mar 1998 15:22:23 -0600
>From: scottn@simtech.com (Scott Nelson)
>To: stuart@sutherland.com
>Subject: VXL & VCS Bug?
>Cc: scottn@simtech.com
>X-Loop-Detect: 1
>
>Hello Stuart
>
>The following module has an "implicit port_reference" - which according
>to the BNF of the Verilog language is not defined. Yet both VXL 2.6 & VCS
4.1
>parse and simulate this without warning an error.
>
> module misc (nstrobe, nstrb0, );
> output nstrobe;
> input [3:0] nstrb0;
>
> assign nstrobe = !( !nstrb0[0] | !nstrb0[1] | !nstrb0[2] |
!nstrb0[3] );
>
> endmodule
>
>instantiated in another module as:
>
> misc u11 (.nstrobe(nstrobe), .nstrb0(nstrb0));
>
>
>It appears both VCS & VXL create a port for the nothing after the last ','
>but naturally with different attributes:
>
>The following are the reult of acc calls made on the 3rd port instance
>returned in:
>
> handle hPort = null;
> while (hPort = acc_next_port(scope_handle, hPort))
> ...
>VXL
>---
>acc_fetch_fullname: null
>acc_fetch_index: 2
>acc_fetch_direction: 0 // *** What is 0 in this case - just undefined?
>acc_fetch_size: 0
>acc_fetch_type: 35 accPort
>acc_fetch_fulltype: 35 accPort
>acc_fetch_loconn: null
>
>
>VCS
>---
>acc_fetch_fullname: null
>acc_fetch_index: 2
>acc_fetch_direction: 0
>acc_fetch_size: 1
>acc_fetch_type: 35 accPort
>acc_fetch_fulltype: 250 accScalarPort
>acc_fetch_loconn: null
>
>Given I am still a relative novice - have I missed something?
>Is this really a bug?
>Is there a good web site for known VXL bugs.
>
>
>
>Thanks
>
>Scott
>
>_______________________________________________________________________
>
> Scott Nelson Phone: 612-631-1858 x 226
> Summit Design, Inc. Fax: 612-631-1830
> 2299 Palmer Drive, Suite 202 E-mail: scottn@sd.com
> New Brighton, MN 55112
>
>
>
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Stuart Sutherland Sutherland HDL Inc.
stuart@sutherland.com 22805 SW 92nd Place
phone: 503-692-0898 Tualatin, OR 97062
www.sutherland.com
Specializing in Verilog HDL consulting and training. Publisher of the
popular Verilog HDL and Verilog PLI quick reference guides.
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