请教大家一个问题，
我写了一个状态机，代码如下：
always @(posedge p0rxc or negedge rst_n)
begin
if(!rst_n)
current_state <= idle;
else
current_state <= next_state;
end
always @(current_state)
begin
case(current_state)
idle : if(read_fifo_empty)
next_state <= idle;
else if(start_read_fifo)
next_state <= first_read;
else
next_state <= idle;
first_read : if(read_fifo_cnt == 16'd7)
next_state <= judge_data_type;
else
next_state <= first_read;
judge_data_type : if(video_data_type)
next_state <= judge_video_range;
else
next_state <= judge_cardNo;
judge_video_range : next_state <= local_forward;
judge_cardNo : next_state <= local_forward;
local_forward : if(forward_video||forward_notvideo||forward_frame)
next_state <= forward;
else
next_state <= local;
local : if(read_fifo_empty)
next_state <= idle;
else
next_state <= local;
forward : if(read_fifo_empty)
next_state <= idle;
else
next_state <= forward;
default : next_state <= idle;
endcase
end
这个状态机下载到fpga是能正常工作的。
问题是在Isim仿真中，当read_fifo_empty=0而start_read_fifo=1时，curent_state为什么不跳转到first_read。如图1.
![]()
图1 状态不转变
然后我将状态机修改如下，再仿真可以看到状态机跳转了。如图2.
always @(posedge p0rxc or negedge rst_n)
begin
case(current_state)
idle : if(read_fifo_empty)
current_state <= idle;
else if(start_read_fifo)
current_state <= first_read;
else
current_state <= idle;
first_read : if(read_fifo_cnt == 16'd7)
current_state <= judge_data_type;
else
current_state <= first_read;
judge_data_type : if(video_data_type)
current_state <= judge_video_range;
else
current_state <= judge_cardNo;
judge_video_range : current_state <= local_forward;
judge_cardNo : current_state <= local_forward;
local_forward : if(forward_video||forward_notvideo||forward_frame)
current_state <= forward;
else
current_state <= local;
local : if(read_fifo_empty)
current_state <= idle;
else
current_state <= local;
forward : if(read_fifo_empty)
current_state <= idle;
else
current_state <= forward;
default : current_state <= idle;
endcase
end
![]()
图2 状态转变
请问为什么前面那个状态机仿真不正确呢？谢谢！ |
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