CODEWITHSUNDEEP
verilog
Amna
Amna

Reputation: 19

Initialize an array using size defined by parameter in verilog

can we initialize arrays using parameter to define size in verilog for example I want

parameter max_neigh=8 , size = 72;
reg [0:8*max_neigh-1]neighbors = size'h010203040304050607;
//or as
reg [0:8*max_neigh-1]neighbors = (8*max_neigh-1)'h010203040304050607;

It gives error: "syntax error near 'h".
Any help will be highly appreciated!
Regards

Upvotes: 1

Views: 4905

Answers (2)

dave_59
dave_59

Reputation: 42623

There is no need to put a size on a hexadecimal(or any base) number as long as you only care that it be extended by zeros and won't be used in a bit-wise expression where the actual size matters(~'h1 is not a good idea).

Upvotes: 1

Krouitch
Krouitch

Reputation: 626

Declaring arrays with parametrized does not generate any problem.
However from what I know you cannot use a parametrized size for a value assignment. You can instead leave the 'size' field empty.

It would look like:

reg [0:8*max_neigh-1]neighbors = 'h010203040304050607;

If you absolutely want to use your size parameter you can do something like:

reg [0:8*max_neigh-1]neighbors = {size{1'b0}};

Which would duplicate the 1'b0 value size in the array, which would be equivalent to 72'h000000000000000000.

BONUS

Be aware that such assignment cannot be synthesised. This is worse than that in fact, the synthesis tool would not report an error, maybe a warning, but simply ignore that assignment. To initialize a register you should use a process.

For example a synchronous process would be with clk a clock input and nrst a reset signal that is active on low-level:

reg [0:8*max_neigh-1]neighbors;
wire [0:8*max_neigh-1]next_neighbors_value;
always@(posedge clk or negedge nrst)
    if(~nrst)
        neighbors <= {72{1'b0}};
    else
        neighbors <= next_neighbors_value;

And btw, 8*8 = 64 and not 72.

Upvotes: 2

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