Vivado synthesis supports some block statements, as follows:
•Block statements group statements together. They are designated by begin and end keywords. Block statements execute the statements in the order listed within the block.
•Vivado synthesis supports sequential blocks only.
•Vivado synthesis does not support parallel blocks.
•All procedural statements occur in blocks that are defined inside modules.
•The two kinds of procedural blocks are initial block and always block
•Verilog uses begin and end keywords within each block to enclose the statements. Because initial blocks are ignored during synthesis, only always blocks are described.
•always blocks usually take the following format. Each statement is a procedural assignment line terminated by a semicolon.
always
begin
statement
.... end