vivado综合时，状态机状态变量出现问题，如何解决？

vivado 2018上行为仿真已经通过了，但是综合后功能仿真出现高阻态，发现是system verilog代码状态机部分next_state变量出现问题，综合信息显示：

[Synth 8-5544] ROM "next_state" won't be mapped to Block RAM because address size (1) smaller than threshold (5)

我非常不理解为什么vivado尝试将我的状态机FSM映射到内存，导致该问题，请问如何解决？
部分代码如下：

localparam STATE_WIDTH=5;
localparam ILLEGAL_STATE=5'd0;
localparam IDLE_STATE=5'd1;
localparam WAIT_CONDITION0_STATE=5'd2;
localparam WAIT_CONDITION1_STATE=5'd4;
localparam LLR_START_READ_CAL_STORE_STATE=5'd8;
localparam LLR_READ_CAL_STORE_STATE=5'd16;

reg [STATE_WIDTH-1:0] current_state;
reg [STATE_WIDTH-1:0] next_state;
always_ff@(posedge clk or posedge reset)
    begin
        if(reset)
        begin
            current_state<=IDLE_STATE;
        end
        else
        begin
            current_state<=next_state;
        end
    end
//state judge
always_comb
begin
    if(reset)
    begin
        next_state=IDLE_STATE; 
    end
    else
    begin
        case(current_state)
            IDLE_STATE:
            begin
                if(...)
                begin
                    next_state=LLR_START_READ_CAL_STORE_STATE; 
                end
                else if(...)
                begin
                    next_state=WAIT_CONDITION1_STATE;
                end
                else if(...)
                begin
                    next_state=WAIT_CONDITION0_STATE;
                end
                else
                begin
                    next_state=IDLE_STATE; 
                end  
            end
          WAIT_CONDITION1_STATE:
          begin
              if(...)
              begin
                 next_state=LLR_START_READ_CAL_STORE_STATE;
              end
              else
              begin
                 next_state=WAIT_CONDITION1_STATE;
              end  
          end
          WAIT_CONDITION0_STATE:
          begin
              if(...)
              begin
                 next_state=LLR_START_READ_CAL_STORE_STATE;
              end
              else
              begin
                 next_state=WAIT_CONDITION0_STATE;
              end                  
          end
         LLR_START_READ_CAL_STORE_STATE:
          begin
          if(...)
            begin
                next_state=IDLE_STATE;
            end
            else if(...)
            begin
                next_state=LLR_READ_CAL_STORE_STATE;
            end
            else
            begin
                next_state=LLR_START_READ_CAL_STORE_STATE;
            end
          end
          LLR_READ_CAL_STORE_STATE:
          begin
            if(...)
            begin
                next_state=IDLE_STATE;
            end
            else
            begin
                next_state=LLR_READ_CAL_STORE_STATE;
            end
          end
          default:
            begin
                 next_state=ILLEGAL_STATE;
            end         
        endcase       
    end
end