Accessing Verilog genvar generated instances in simulation code - simulation

Question

This is a Verilog releated question. I am working with XILINX ISE as a dev environment.
I am trying to access variables in the simulation that are automatically generated using genvar but I am receiving the following error -> HDLCompiler:71
Problem Example:
genvar i;
generate
for(i=0; i < N; i=i+1)
begin:Sys_Modules
TypeXModule #(.width(10)) xmod(.dataY(dataY)));
end
endgenerate
When I ran synthesis or simulation I can see that Sys_Modules[0..N-1].xmod instances are created.
When I try to add a line to the simulation accessing the Sys_Modules array:
Sys_Modules[i].xmod.dataY
I get the following error:
HDLCompiler:71 dataY is not declared under prefix xmod
Is there any way to access automatically generated values in the simulation?
Thanks!

Answer 1

You cannot use cross-instance hierarchical references in synthesized Verilog.

Answer 2

It is legal to write a hierarchical reference to a generated instance. The functionality is described in sections 2.7.2 and 12.1.3 of the IEEE Verilog standard. However, the instance subscript must be a constant so that it can be resolved at compile time.

Answer 3

I think you're out of luck. Simulators don't seem to like out-of-module references (OOMRs) pointing into generated blocks as you've discovered.
I encountered a similar problem recently when making a parameterizable testbench monitor. I'd a variable number of sub-blocks instantiated depending on a parameter. Within this, I needed to have a toplevel .start() task that called the .start() tasks in each of the instantiated modules. I couldn't use a for loop to do this because of this OOMR problem.
So I ended up having to:
define a reg that the toplevel .start() task toggled
write an always # block triggered on this reg
write another generate section within this always block to call .start() on each of the sub-modules.
If you really need to peek into your generated modules, maybe you could try a workaround like above? For instance, have a bus at the toplevel, and use agenerate statement to peek inside your original generated instantiations to copy/assign interesting signals on to this toplevel bus.

Answer 4

I have found and used another solution, posting it here in case someone will find it useful. Worked for me in Vivado 2020.
Steps:
in tb: declare all data you need to print (declare wires)
ex:for Sys_Modules[0..N-1], wanting Sys_Modules[i].xmod.dataY =>
tb: wire [0:N-1][`DATA_SIZE-1:0] tb_Sys_Modules_dataY;
generate all connections using a generate block
ex: (N should be a define/parameter)
for(i = 0 ; i < N ;i = i + 1)
assign tb_Sys_Modules_dataY[i] = Sys_Modules[i].xmod.dataY;
$display wire from tb:
ex:
$display("%d",tb_Sys_Modules_dataY[i]);