HBLbits_Verilog Basic_Vectorr

 HBLbits_Verilog Basic_Vectorr

Given an 8-bit input vector [7:0], reverse its bit ordering.

module top_module (
input [7:0] in,
output [7:0] out
);

assign {out[0],out[1],out[2],out[3],out[4],out[5],out[6],out[7]} = in;

/*
// I know you're dying to know how to use a loop to do this:
// Create a combinational always block. This creates combinational logic that computes the same result
// as sequential code. for-loops describe circuit *behaviour*, not *structure*, so they can only be used 
// inside procedural blocks (e.g., always block).
// The circuit created (wires and gates) does NOT do any iteration: It only produces the same result
// AS IF the iteration occurred. In reality, a logic synthesizer will do the iteration at compile time to
// figure out what circuit to produce. (In contrast, a Verilog simulator will execute the loop sequentially
// during simulation.)
always @(*) begin
for (int i=0; i<8; i++) // int is a SystemVerilog type. Use integer for pure Verilog.
out[i] = in[8-i-1];
end

// It is also possible to do this with a generate-for loop. Generate loops look like procedural for loops,
// but are quite different in concept, and not easy to understand. Generate loops are used to make instantiations
// of "things" (Unlike procedural loops, it doesn't describe actions). These "things" are assign statements,
// module instantiations, net/variable declarations, and procedural blocks (things you can create when NOT inside 
// a procedure). Generate loops (and genvars) are evaluated entirely at compile time. You can think of generate
// blocks as a form of preprocessing to generate more code, which is then run though the logic synthesizer.
// In the example below, the generate-for loop first creates 8 assign statements at compile time, which is then
// synthesized.
// Note that because of its intended usage (generating code at compile time), there are some restrictions
// on how you use them. Examples: 1. Quartus requires a generate-for loop to have a named begin-end block
// attached (in this example, named "my_block_name"). 2. Inside the loop body, genvars are read only.
generate
genvar i;
for (i=0; i<8; i = i+1) begin: my_block_name
assign out[i] = in[8-i-1];
end
endgenerate
*/

endmodule