--- Quote Start ---
square brackets mean execute the command and return the value:
> set sum [expr 3.0 + 4.0 + 5.0]
> 12.0
Curly brackets mean everything inside should be take literally:
> set sum {expr 3.0 + 4.0 +5.0}
returns:
> expr 3.0 + 4.0 + 5.0
(i.e. sum is a list, where the first member is expr, the second member is 3.0, etc.
Quotation marks are used for a list also, but not as literal:
>set sum "a [expr 3.0 + 4.0] b"
sum is now a list, with the first member a, the second member 7.0, and the last member b
The big problem is that Quartus(and most tools) use square brackets for node indices. So if you want a simple node:
get_ports data
get_ports "data"
get_ports {data}
all three of these are the same thing. But if grabbing a member of a bus:
get_ports data[3]
get_ports "data[3]"
get_ports "data\[3\]"
get_ports {data[3]"
The first two will fail since it will try to execute the command 3. The second two will work with what you want. But if you're passing in a variable, you need to use quotes:
get_ports "data\[$i\]"
It takes a little getting used to, but all languages tend to be confusing in this area. (Or they're too strict and severely limited if they don't have lots of options.)
--- Quote End ---
Thanks very much for the detailed explaination.
Is there any book about FPGA you have written? I think you are qualified for a writer.
Honored Contributor
