while(cond) blockexecutes block as long as the condition cond is true. If cond is false, it falls through to the next statement in exactly zero time. The last statement of block must be a wait statement. As an example,
reg [1:0] x; initial x = 0; always begin while(x < 3) begin x = x + 1; wait(1); end x = 0; endresults in the sequence 0,1,2,3,0,1,...for x.
A for loop, on the other hand, must have static upper and lower bounds, and is unrolled at compile time. Thus, for example,
for(i = 0; i < 4; i = i + 1) block(i)is exactly equivalent to
block(0); block(1); block(2); block(3);The block in this case need not contain a wait statement.