blocking and nonblocking assignment

• continous assignment data flow model outside of always blocks 有 assign keyword 一旦右边有变化 左边立刻更新
• procdural assignment within a always block 没有 assign keyword 只有当always triggerd 左边才会更新 两种方式
  • blocking(immedia): =
  • nonblocking(deferred): ⇐

module comb_block_nonblock{
	input a,b,c,
	output reg x
};
	always @(a,b,c)
	begin
		x=a; //block the execution of the next statement 执行这一条语句
		x=x^b;
		x=x|c;
	end
	
endmodule
 

module comb_block_nonblock{
	input a,b,c,
	output reg x
};
	always @(a,b,c)
	begin
		x<=a; //block the execution of the next statement 执行这一条语句
		x<=x^b;
		x<=x|c;
	end
	
endmodule

unblocking assignment should not be used with combinational circuit 阻塞语句是有顺序的

module ff_block_nonblock{
	input D,clk,
	output reg  Q1,Q2
};
 
always @(posedge clk)
begin
	Q1=D;
	Q2=Q1;
end
 
 
endmodule
 

这样写 vivado会知道 q1 和q2都是用的d的值 最后的图像就不会是两个d latch 了 。 改变顺序

begin
	Q2=Q1;
	Q1=D;
end

nonblock

//顺序不重要
	Q2<=Q1;
	Q1<=D;
 

takeaway: using blocking assignment when you use combination of circuits using nonblocking assignment when you use sequential sircuits