clk_ctrl.v

module clk_ctrl (
    input  wire     SYSCLK,
    input  wire     NRST,
    input  wire     EXPCLK,
    input  wire     EXP_NRST,

    output wire     CSYSREQ_CD_sys,
    input  wire     CSYSACK_CD_sys,
    input  wire     CACTIVE_CD_sys,
    
    output wire     CSYSREQ_CD_exp,
    input  wire     CSYSACK_CD_exp,
    input  wire     CACTIVE_CD_exp
);

parameter  IDLE=2'b00, REQ=2'b01, ACK=2'b10, ACT=2'b11;
reg [1:0] state_sys;
reg [1:0] state_sys_next;

reg [1:0] state_exp;
reg [1:0] state_exp_next;

reg CSYSREQ_CD_sys_reg;
reg SYS_ACT;
reg CSYSREQ_CD_exp_reg;
reg EXP_ACT;


always @(posedge SYSCLK or negedge NRST) begin
    if (!NRST) begin
        state_sys <= IDLE;
        CSYSREQ_CD_sys_reg <= 0;
        SYS_ACT<=0;
    end
    else 
        state_sys <= state_sys_next;
end

always @(*) begin
    state_sys_next = state_sys;
    case(state_sys)
        IDLE : begin
            if(!SYS_ACT)
                state_sys_next = REQ;
        end
        REQ: begin
            CSYSREQ_CD_sys_reg = 1;
            state_sys_next = ACK;
        end
        ACK: begin
            if(CSYSACK_CD_sys) begin
                $display("CLK CTRL: System clock enable acknowledged");
                state_sys_next = ACT;
            end
        end
        ACT: begin
            if(CACTIVE_CD_sys) begin
                $display("CLK CTRL: System clock active");
                SYS_ACT = 1;
                state_sys_next = IDLE;
            end
        end
    endcase
end

assign CSYSREQ_CD_sys = CSYSREQ_CD_sys_reg;


always @(posedge EXPCLK or negedge EXP_NRST) begin
    if (!EXP_NRST) begin
        state_exp <= IDLE;
        CSYSREQ_CD_exp_reg <= 0;
        EXP_ACT<=0;
    end
    else 
        state_exp <= state_exp_next;
end

always @(*) begin
    state_exp_next = state_exp;
    case(state_exp)
        IDLE : begin
            if(!EXP_ACT)
                state_exp_next = REQ;
        end
        REQ: begin
            CSYSREQ_CD_exp_reg = 1;
            state_exp_next = ACK;
        end
        ACK: begin
            if(CSYSACK_CD_exp) begin
                $display("CLK CTRL: Expansion clock enable acknowledged");
                state_exp_next = ACT;
            end
        end
        ACT: begin
            if(CACTIVE_CD_exp) begin
                $display("CLK CTRL: Expansion clock active");
                SYS_ACT = 1;
                state_exp_next = IDLE;
            end
        end
    endcase
end


assign CSYSREQ_CD_exp = CSYSREQ_CD_exp_reg;



endmodule