verilog中always双边触发

### Verilog Always Block Edge-Triggered on Both Rising and Falling Edges In Verilog, an `always` block can be configured to trigger on both the rising (`posedge`) and falling (`negedge`) edges of a signal such as a clock. This dual-edge triggering mechanism allows for more efficient use of clock cycles in certain applications where processing needs occur not only during one phase but also another. To implement this functionality correctly without introducing potential glitches or hazards mentioned elsewhere[^2], consider using separate sensitivity lists for each edge within nested blocks: ```verilog module dual_edge_triggered ( input wire clk, input wire reset_n, output reg q ); always @(posedge clk or negedge reset_n) begin : pos_block if (!reset_n) q <= 0; else // Actions triggered by positive edge go here. q <= ~q; // Example action end always @(negedge clk or negedge reset_n) begin : neg_block if (!reset_n) q <= 0; else // Actions triggered by negative edge go here. q <= ~q; // Same example action for demonstration purposes end endmodule ``` Alternatively, combining conditions inside a single `always` block with appropriate logic ensures that actions are taken based on either edge transition while maintaining clarity about which transitions cause what effects: ```verilog module dual_edge_triggered_combined ( input wire clk, input wire reset_n, output reg q ); always @(*) begin if (!reset_n) q <= 0; else if (clk != prev_clk) begin unique case ({prev_clk, clk}) 2'b01: /* Action for posedge */ ; 2'b10: /* Action for negedge */ ; endcase prev_clk = clk; end end reg prev_clk; initial prev_clk = clk; endmodule ``` However, note that directly writing `always @(posedge clk or negedge clk)` is syntactically incorrect because it would imply simultaneous occurrence of mutually exclusive events unless handled through combinational logic checks like shown above. For practical implementation aiming at synthesis tools understanding, prefer separating into distinct processes handling their respective edges explicitly rather than relying solely upon detecting changes via combinational means due to possible timing issues introduced when inferring flip-flops from non-standard constructs. --related questions-- 1. How does adding asynchronous resets affect designs utilizing dual-edge detection? 2. What considerations should designers take regarding power consumption when implementing dual-edge triggered circuits? 3. Can you explain how metastability might impact systems employing multiple clock domains especially concerning edge-sensitive components? 4. Are there specific FPGA architectures better suited for supporting dual-edge triggered operations efficiently?