module command(
        CLK,
        RESET_N,
        SADDR,
        NOP,
        READA,
        WRITEA,
        REFRESH,
        PRECHARGE,
        LOAD_MODE,
        REF_REQ,
		INIT_REQ,
		PM_STOP,
		PM_DONE,
        REF_ACK,
        CM_ACK,
        OE,
        SA,
        BA,
        CS_N,
        CKE,
        RAS_N,
        CAS_N,
        WE_N
        );

`include        "Sdram_Params.h"

input                           CLK;                    // System Clock
input                           RESET_N;                // System Reset
input   [`ASIZE-1:0]            SADDR;                  // Address
input                           NOP;                    // Decoded NOP command
input                           READA;                  // Decoded READA command
input                           WRITEA;                 // Decoded WRITEA command
input                           REFRESH;                // Decoded REFRESH command
input                           PRECHARGE;              // Decoded PRECHARGE command
input                           LOAD_MODE;              // Decoded LOAD_MODE command
input                           REF_REQ;                // Hidden refresh request
input							INIT_REQ;				// Hidden initial request
input							PM_STOP;				// Page mode stop
input							PM_DONE;				// Page mode done
output                          REF_ACK;                // Refresh request acknowledge
output                          CM_ACK;                 // Command acknowledge
output                          OE;                     // OE signal for data path module
output  [11:0]                  SA;                     // SDRAM address
output  [1:0]                   BA;                     // SDRAM bank address
output  [1:0]                   CS_N;                   // SDRAM chip selects
output                          CKE;                    // SDRAM clock enable
output                          RAS_N;                  // SDRAM RAS
output                          CAS_N;                  // SDRAM CAS
output                          WE_N;                   // SDRAM WE_N

            
reg                             CM_ACK;
reg                             REF_ACK;
reg                             OE;
reg     [11:0]                  SA;
reg     [1:0]                   BA;
reg     [1:0]                   CS_N;
reg                             CKE;
reg                             RAS_N;
reg                             CAS_N;
reg                             WE_N;



// Internal signals
reg                             do_reada;
reg                             do_writea;
reg                             do_refresh;
reg                             do_precharge;
reg                             do_load_mode;
reg								do_initial;
reg                             command_done;
reg     [7:0]                   command_delay;
reg     [1:0]                   rw_shift;
reg                             do_act;
reg                             rw_flag;
reg                             do_rw;
reg     [6:0]                   oe_shift;
reg                             oe1;
reg                             oe2;
reg                             oe3;
reg                             oe4;
reg     [3:0]                   rp_shift;
reg                             rp_done;
reg								ex_read;
reg								ex_write;

wire    [`ROWSIZE - 1:0]        rowaddr;
wire    [`COLSIZE - 1:0]        coladdr;
wire    [`BANKSIZE - 1:0]       bankaddr;

assign   rowaddr   = SADDR[`ROWSTART + `ROWSIZE - 1: `ROWSTART];          // assignment of the row address bits from SADDR
assign   coladdr   = SADDR[`COLSTART + `COLSIZE - 1:`COLSTART];           // assignment of the column address bits
assign   bankaddr  = SADDR[`BANKSTART + `BANKSIZE - 1:`BANKSTART];        // assignment of the bank address bits



// This always block monitors the individual command lines and issues a command
// to the next stage if there currently another command already running.
//
always @(posedge CLK or negedge RESET_N)
begin
        if (RESET_N == 0) 
        begin
                do_reada        <= 0;
                do_writea       <= 0;
                do_refresh      <= 0;
                do_precharge    <= 0;
                do_load_mode    <= 0;
				do_initial		<= 0;
                command_done    <= 0;
                command_delay   <= 0;
                rw_flag         <= 0;
                rp_shift        <= 0;
                rp_done         <= 0;
				ex_read			<= 0;
				ex_write		<= 0;
        end
        
        else
        begin

//  Issue the appropriate command if the sdram is not currently busy
			if( INIT_REQ == 1 )
			begin
                do_reada        <= 0;
                do_writea       <= 0;
                do_refresh      <= 0;
                do_precharge    <= 0;
                do_load_mode    <= 0;
				do_initial		<= 1;
                command_done    <= 0;
                command_delay   <= 0;
                rw_flag         <= 0;
                rp_shift        <= 0;
                rp_done         <= 0;
				ex_read			<= 0;
				ex_write		<= 0;
			end
			else
			begin
				do_initial		<= 0;
				
                if ((REF_REQ == 1 | REFRESH == 1) & command_done == 0 & do_refresh == 0 & rp_done == 0         // Refresh
                        & do_reada == 0 & do_writea == 0)
                        do_refresh <= 1;         
                else
                        do_refresh <= 0;

                if ((READA == 1) & (command_done == 0) & (do_reada == 0) & (rp_done == 0) & (REF_REQ == 0))    // READA
                begin
				        do_reada <= 1;
						ex_read <= 1;
				end
                else
                        do_reada <= 0;
                    
                if ((WRITEA == 1) & (command_done == 0) & (do_writea == 0) & (rp_done == 0) & (REF_REQ == 0))  // WRITEA
                begin
				        do_writea <= 1;
						ex_write <= 1;
				end
                else
                        do_writea <= 0;

                if ((PRECHARGE == 1) & (command_done == 0) & (do_precharge == 0))                              // PRECHARGE
                        do_precharge <= 1;
                else
                        do_precharge <= 0;
 
                if ((LOAD_MODE == 1) & (command_done == 0) & (do_load_mode == 0))                              // LOADMODE
                        do_load_mode <= 1;
                else
                        do_load_mode <= 0;
                                               
// set command_delay shift register and command_done flag
// The command delay shift register is a timer that is used to ensure that
// the SDRAM devices have had sufficient time to finish the last command.

                if ((do_refresh == 1) | (do_reada == 1) | (do_writea == 1) | (do_precharge == 1)
                     | (do_load_mode == 1))
                begin
                        command_delay <= 8'b11111111;
                        command_done  <= 1;
                        rw_flag <= do_reada;                                                  
                end
                
                else
                begin
                        command_done        <= command_delay[0];                // the command_delay shift operation
                        command_delay		<= (command_delay>>1);
                end 
                
 
 // start additional timer that is used for the refresh, writea, reada commands               
                if (command_delay[0] == 0 & command_done == 1)
                begin
                	rp_shift <= 4'b1111;
                	rp_done <= 1;
                end
                else
                begin						
					if(SC_PM == 0)
					begin
						rp_shift	<= (rp_shift>>1);
                    	rp_done		<= rp_shift[0];
					end
					else
					begin
						if( (ex_read == 0) && (ex_write == 0) )
						begin
							rp_shift	<= (rp_shift>>1);
        	            	rp_done		<= rp_shift[0];
						end
						else
						begin
							if( PM_STOP==1 )
							begin
								rp_shift	<= (rp_shift>>1);
        	      		      	rp_done     <= rp_shift[0];
								ex_read		<= 1'b0;
								ex_write	<= 1'b0;