[How to exchange data between PL and PS?]

@zygot Sorry for the late reply. I've been trying a bunch of things to try to get anything to work. I'm trying to go with the UART1 through EMIO method, but I can't figure out how to connect my code to it. I've included my test code, a screenshot of the block diagram, and a ZIP of my project folder. I don't expect you to help, but if you or anyone else can I would appreciate it a ton. :)

When I try to generate the bitstream I get an "Unconstrained Logical Port" error for LED, which I don't understand. I know I must be doing something wrong but I don't know what...

 

module top(
    output LED,
    input clk    
    );
	 
integer counter;
reg state;

always @ (posedge clk) begin
    counter <= counter + 1;
	 if(counter >= 50000000 )begin
		counter <= 0;
		state <= !state;
	 end
end
	 
assign LED = state;	 

endmodule

uart.zip

[How to exchange data between PL and PS?]

I have an Arty Z7-20 and I'm trying to figure out how to get arbitrary data from HDL in the PL to the PS, to be printed over USB UART. I've followed this tutorial and I understand how to connect GPIO to the PS and to print to a serial terminal, but I can't figure out how to send data from the PL to the PS.

Say I want to implement a simple CPU in the PL, that I can interact with through a serial terminal. How could I send, for example, the output of a program (like printing "hello world") run on the CPU in PL to the PS to then be output to a serial terminal, and vice versa (typing in the serial terminal to send data to the CPU in the PL)?

I want to do o this because I am interested in architectures, compilers, emulators and the like and would like to learn FPGAs by eventually implementing a CPU on the FPGA side. I've been stuck for so long by the USB UART being accessible only through the PS. I essentially just need a bridge on the PS to exchange data from the PL to the PC's serial terminal.

Thank you to anyone that can help!