DE1-SoC FPGA密码门锁按键触发直接跳至S8问题排查求助

我正在DE1-SoC FPGA开发板上实现一款密码验证门锁系统：

• 预设有效密码为123、122、121，输入正确后门锁解锁
• 按键映射：KEY0对应数字'1'，KEY1对应数字'2'，KEY2对应数字'3'，KEY3对应数字'4'
• 复位信号RST分配至SW0，开发板按键为低电平有效
• 状态跳转逻辑参考状态图：

当前遇到异常：初始处于S0状态时，按下KEY0按键，系统会直接跳至S8状态（可通过七段显示器HEX0、HEX1的显示确认）。请问我的Verilog代码是否存在问题？

以下是我的Verilog代码：

module rewardsys(KEY0,KEY1,KEY2,KEY3,HEX0,HEX1,RST);
input KEY0,KEY1,KEY2,KEY3,RST;
output reg [6:0] HEX0,HEX1;
parameter s0=4'b0000;
parameter s1=4'b0001;
parameter s2=4'b0010;
parameter s3=4'b0011;
parameter s4=4'b0100;
parameter s5=4'b0101;
parameter s6=4'b0110;
parameter s7=4'b0111;
parameter s8=4'b1000;

reg[3:0] cstate,nstate;

always@(posedge KEY0,posedge KEY1,posedge KEY2,posedge KEY3,negedge RST) begin
  if(RST==0)
     cstate<=s0;
  else
     cstate<=nstate;
end

always @ (posedge KEY0,posedge KEY1, posedge KEY2, posedge KEY3) begin
  case(cstate)
     s0:
        begin                     //display S0
          HEX1=7'b0010010;
          HEX0=7'b1000000;
          if(KEY0==0)
             nstate=s1;
          else if ((KEY1==0) | (KEY2==0) | (KEY3==0))
             nstate=s6;
          else
             nstate=s0;
        end

     s1:
        begin                     //display S1
          HEX1=7'b0010010;
          HEX0=7'b1111001;
          if(KEY1==0)
             nstate=s2;
          else if ((KEY0==0) | (KEY2==0) | (KEY3==0))
             nstate=s7;
          else
             nstate=s1;
        end

     s2:
        begin                     //display S2
          HEX1=7'b0010010;
          HEX0=7'b0100100;            
          if(KEY2==0)
             nstate=s3;
          else if(KEY1==0)
             nstate=s4;
          else if(KEY0==0)
             nstate=s5;
          else if(KEY3==0)
             nstate=s8;
          else
             nstate=s2;
        end

     s3:
        begin                     //display S3
          HEX1=7'b0010010;
          HEX0=7'b0110000;
        end

     s4:
        begin                     // display S4
          HEX1=7'b0010010;
          HEX0=7'b0011001;
        end

     s5:
        begin                     //display S5
          HEX1=7'b0010010;
          HEX0=7'b0010010;
        end

     s6:
        begin                     //display S6
          HEX1=7'b0010010;
          HEX0=7'b0000010;
          if ((KEY0==0) | (KEY1==0) | (KEY2==0) | (KEY3==0))
             nstate=s7;
          else
             nstate=s6;
        end

     s7:
        begin                     //display S7
          HEX1=7'b0010010;
          HEX0=7'b1111000;
          if ((KEY0==0) | (KEY1==0) | (KEY2==0) | (KEY3==0))
             nstate=s8;
          else
             nstate=s7;
        end

     s8:
        begin                     //display S8
          HEX1=7'b0010010;
          HEX0=7'b0000000;
          nstate=s8;
        end
        
     default:
        nstate=s0;
  endcase
end
endmodule

感谢您的帮助！

内容的提问来源于stack exchange，提问作者IRFAN AZEEZ