implementation of stdin and $feof in icarus verilog
Jason Zheng
The Verilog 2001 reference defines stdin, stdout, and stderr as
pre-opened file descriptors (0x80000001- 0x80000003). However, when I
tried to use stdin in Icarus, the stdin does not seem to be opened.
In addition, although I haven't seen it in the Verilog 2001 reference,
some examples on the web have used "$feof" to test the EOF for a file
descriptor. Icarus doesn't reject it as a syntax error, but when I
tried to use $feof on stdin, it seems to think that stdin has not
reached EOF even though $fget returns FFFFFFFF.
Here's my test code:
`timescale 1ns / 100ps
module mytb;
parameter clk_per = 10;
parameter STDIN = 32'h8000_0001;
reg CLK;
integer tmp;
initial
begin
CLK = 0;
forever
#(clk_per/2) CLK = ~CLK;
end
always @ (negedge CLK)
if (!$feof(STDIN))
begin
tmp = $fgetc(STDIN);
$display("%x",tmp);
end
else
$finish;
endmodule
Any thoughts, Steve?
Stephen Williams
> Hi,
>
> The Verilog 2001 reference defines stdin, stdout, and stderr as
> pre-opened file descriptors (0x80000001- 0x80000003). However, when I
> tried to use stdin in Icarus, the stdin does not seem to be opened.
You've got the wrong numbers there. The pre-opened descriptors
are 0x80000000 - 0x80000002.
> In addition, although I haven't seen it in the Verilog 2001 reference,
> some examples on the web have used "$feof" to test the EOF for a file
> descriptor. Icarus doesn't reject it as a syntax error, but when I
> tried to use $feof on stdin, it seems to think that stdin has not
> reached EOF even though $fget returns FFFFFFFF.
It works in Icarus Verilog. I fixed your sample program and it
runs fine.
> parameter clk_per = 10;
> parameter STDIN = 32'h8000_0001;
There's your problem. Standard input is 32'h8000_0000. The value
you have there is for standard output.
--
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."
Jason Zheng
Stephen Williams <spam...@icarus.com> wrote:
>
> > parameter clk_per = 10;
> > parameter STDIN = 32'h8000_0001;
>
> There's your problem. Standard input is 32'h8000_0000. The value
> you have there is for standard output.
Doh! Thanks!