read_master.v

altera 的示例ip

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module read_master
	(
		//Global Avalon interface siganals    
		gls_clk,
		gls_reset_n,
		//Signals for Avalon-MM master port
		avm_m1_address,
		//address,		  // debug - full address output
		avm_m1_byteenable,  // for future byte lane control  
		avm_m1_read_n,
		avm_m1_readdata,
		avm_m1_waitrequest,
		// Signals from slave registers
		addr_reg,
		len_reg,
		go,
		
		avm_m1_byteenable_mask,  // debug - for byteenable mask values
		
		read_busy,
		data_in_ready,
		count,		// debug - check count value and for future enhancement
		data_to_process
		
	);

		input gls_clk;
		input gls_reset_n;

		output [31:0]avm_m1_address;
		//output [31:0]address;		  // debug - full address output
		output [3:0]avm_m1_byteenable;  //for future byte lane control  
		output avm_m1_read_n;
		input [31:0] avm_m1_readdata;
		input avm_m1_waitrequest;

		input [31:0]addr_reg;
		input [15:0]len_reg;
		input go;
		
		output [3:0]avm_m1_byteenable_mask;  // debug - for byteenable mask values
		
		output read_busy;
		output data_in_ready;
		output [15:0]count;  // debug - check count value and  for future enhancement
		output [31:0]data_to_process;


wire [31:0] avm_m1_address = { addr[31:2], 2'b0 }; // Lower address bits are not used assume world aligned addresses

//wire [31:0] address = addr;

// Check for valid read data on the master port by looking for waitrequest with each read
wire data_in_ready = ( (avm_m1_read_n == 1'b0) && !avm_m1_waitrequest) ? 1'b1 : 1'b0;

// passing readdata to task logic
// mask data to process based on byteenable mask

assign data_to_process[31:0] = 	(avm_m1_byteenable_mask == 4'b0001) ? ( 32'h000000FF & avm_m1_readdata[31:0]) :
						(avm_m1_byteenable_mask == 4'b0011) ? ( 32'h0000FFFF & avm_m1_readdata[31:0]) :
						(avm_m1_byteenable_mask == 4'b0111) ? ( 32'h00FFFFFF & avm_m1_readdata[31:0]) :
															 avm_m1_readdata[31:0];
reg [31:0] addr;
reg avm_m1_read_n;
reg [15:0] count_tmp;
wire [3:0] avm_m1_byteenable = 4'b1111;  // drive byteenables high
reg [3:0] avm_m1_byteenable_mask;
reg read_busy;

//Statemachine block for controlling read master signals 

	always @(posedge gls_clk or negedge gls_reset_n)
	begin
		if (gls_reset_n == 1'b0)
			begin
			count_tmp <= 'b0;
			read_busy <= 1'b0;
			addr <= 'b0;
			avm_m1_byteenable_mask <= 4'b0000;
			avm_m1_read_n <= 1'b1;			
			read_busy <= 1'b0;
			end
		else if (go)					// loads count and start read master statemachine
			begin
			count_tmp <= len_reg - 3'h4; 		// decrement count for this initial load/read state
			addr <= addr_reg ;			// loads address - must be 32-bit word aligned addess
			avm_m1_byteenable_mask <= 4'b1111;
			avm_m1_read_n <= 1'b1;   
			read_busy <= 1'b1;
			end
		else if (count > 3 && data_in_ready)  	// Main loop for read master statemachine
			begin
			count_tmp <= count_tmp - 3'h4;
			addr <= addr + 3'h4;
			avm_m1_byteenable_mask <= 4'b1111;		// assert byteenable mask byte lane(s) 3,2,1,0
			avm_m1_read_n <= 1'b0;
			read_busy <= 1'b1;
			end
		else if (count == 3 && data_in_ready) 	// Last read for un-aligned word lengths - 3 bytes
			begin
			count_tmp <= count_tmp - 3'h3;
			addr <= addr + 3'h4;
			avm_m1_byteenable_mask <= 4'b0111;		// assert byteenable mask byte lane(s) 2,1,0
			avm_m1_read_n <= 1'b0;
			read_busy <= 1'b1;
			end	
		else if (count == 2 && data_in_ready) 	// Last read for un-aligned word lengths - 2 bytes	
			begin
			count_tmp <= count_tmp - 3'h2;
			addr <= addr + 3'h4;
			avm_m1_byteenable_mask <= 4'b0011;		// assert byteenable mask byte lane(s) 1,0
			avm_m1_read_n <= 1'b0;
			read_busy <= 1'b1;
			end				
		else if (count == 1 && data_in_ready)	// Last read for un-aligned word lengths - 1 bytes
			begin
			count_tmp <= count_tmp - 3'h1;
			addr <= addr + 3'h4;
			avm_m1_byteenable_mask <= 4'b0001;		// assert byteenable mask byte lane(s) 0
			avm_m1_read_n <= 1'b0;
			read_busy <= 1'b1;
			end			
		else if (count ==0 && !data_in_ready) 	// Hold outputs if waitrequest asserted during last read cycle
			begin
			count_tmp <= count_tmp;
			addr <= addr ;
			avm_m1_byteenable_mask <= avm_m1_byteenable_mask;
			avm_m1_read_n <= avm_m1_read_n;  
			read_busy <= read_busy;	
			end
				
		else if (count ==0)				// byte count is zero and the exit condition for read master statemachine
			begin
			addr <= 'b0;						// clear address
			avm_m1_byteenable_mask <= 4'b0000;		// clear byteenables
			avm_m1_read_n <= 1'b1; 				// stop reading
			read_busy <= 1'b0;					// deassert busy bit	
			end
		else   // Starts the read cycle after a load or holds master outputs static when waitrequest asserted
			begin
			count_tmp <= count_tmp;
			addr <= addr ;
			avm_m1_byteenable_mask <= avm_m1_byteenable_mask;
			avm_m1_read_n <= 1'b0;   		// starts the read cycle
			read_busy <= 1'b1;				

			end
       
	end

assign count = count_tmp;

endmodule