How can I read button presses through the Avalon bus?

Gabe · ‎06-07-2019

Hello,

I have been trying to create a simple Avalon-MM Master to read from a PIO slave (push buttons), however I am reading only 0's on the readdata line.

Relevant code:

        wire [31:0] master_0_master_address;
	wire             master_0_master_read;  
	wire [31:0] master_0_master_readdata;
	
	reg [1:0]currentState;
	reg [1:0]nextState;
	reg [31:0] data;
	
	reg [31:0] address;
	reg read;
	
	assign master_0_master_address = address;
	assign master_0_master_read = read;
	
	assign led11[3:0] = ((reset_reset_n == 0)) ? 4'b1111 : (data[3:0]);
	
	
	always @ (*) begin
	if(~reset_reset_n)
	begin
		data <= 32'b0;
		nextState <= 2'b0;
	end
	else begin
		case (currentState) 
		2'b0: begin
			
			address <= 32'b100000;
			read <= 1;
			
			if(master_0_master_waitrequest)
				nextState <= 2'b10;
			else
				nextState <= 2'b1;
			end
			
		2'b1: begin
			
			read <= 0;
			data <= master_0_master_readdata;
			nextState <= 2'b0;
			
			end
			
		2'b10: begin
			if(master_0_master_waitrequest)
				nextState <= 2'b10;
			else
				nextState <= 2'b1;
		
		end
		
		endcase
		end
	end
		
	
	always @ (posedge clk_clk or negedge reset_reset_n)
	begin
	if(~reset_reset_n)
		currentState <= 0;
	else
		currentState <= nextState;
	end

And the Qsys system:

sstrell · ‎06-07-2019

I'm guessing that the signal names preceded by "master_" are your interface signals because I don't see a port list for your component. Is that correct?

Have you tried just leaving read enabled all the time and just do reads on waitrequest going low?

#iwork4intel

Gabe · ‎06-10-2019

Yes, the signals preceded by "master_" are my interface signals. I have somehow managed to get it working. However, I have noticed some weird behavior: No matter the address I place on the master_0_address line, the state machine reads the pushbuttons' data register just fine. But if I add another PIO slave (LEDs) to the project, assign addresses, and then generate the files, then my code does not work anymore - I get 0's again. Seems like the issue is with slave addressing.

When I add the second PIO slave, Qsys assigns 0x0000_0000 to the pushbuttons, and 0x0000_0010 to the LEDs. To read from the pushbuttons' data register, I do master_0_address <= 32'b0. I am not sure if I need to add an offset to the address shown in Qsys or.. According to this document, the data register comes first, so there is a 0 offset to the address shown in Qsys.

Thanks for your help.