I don't use timescale much, so I could be just making a stupid
mistake, but I'm getting unexpected behavior. Howard reports that
he's seen this with ModelSim too, so maybe it's just us.
Anyhow, I have this at the top of a couple of files:
`timescale 1ns / 1ps
My understanding is that this means that the time precision is 1ps,
but if you do #10, for example, that still means 10ns. I'm finding
that this isn't consistent, where some parts of my code are in the ns
timescale and others are in the ps timescale.
Anyone got any ideas?
Below is some of my code. The clocks are being computed on the ns
timescale, while all the delays in the initial block at the end appear
to be in the ps timescale unless I comment out all of the timescale
directives.
module test_fifo;
parameter fifo_depth = 256;
parameter fifo_width = 256;
parameter addr_bits = 8;
reg RESET_N;
reg CLOCK_IN;
initial begin
CLOCK_IN = 0;
forever #5 CLOCK_IN = !CLOCK_IN;
end
reg CLOCK_OUT;
initial begin
CLOCK_OUT = 0;
forever #4 CLOCK_OUT = !CLOCK_OUT;
end
wire [fifo_width-1:0] DOUTi;
reg [fifo_width-1:0] DINi;
reg ENQi, DEQi;
wire VALIDi, FULLi, EMPTYi, FULLo, EMPTYo;
wire [addr_bits:0] FREEi, COUNTi, FREEo, COUNTo;
reg [fifo_width-1:0] expect_DOUT;
initial begin
$dumpfile( "test.vcd" );
$dumpvars;
expect_DOUT = 0;
ENQi = 0;
DEQi = 0;
RESET_N = 1;
#20;
RESET_N = 0;
#20;
RESET_N = 1;
#20;
DINi = 'hdeadbeef;
ENQi = 1;
#10;
ENQi = 0;
#100;
DEQi = 1;
#10;
//DEQi = 0;
#100;
//$finish;
DEQi = 1;
ENQi = 1;
for (DINi=0; DINi<1000; DINi = DINi + 1) begin
#10;
//ENQi = !ENQi;
end
ENQi = 0;
#1000;
$finish;
end
--
Timothy Normand Miller
http://www.cse.ohio-state.edu/~millerti
Open Graphics Project
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