FOMU: UART over USB

[BrunoLevy]

Add a UART to the FOMU (needs a USB core + UART over USB)

[Mecrisp]

Hi Bruno,

I have an USB-Serial core adapted from a mix of USB logic by Luke Valenty, Lawrie Griffiths and David Williams in Mecrisp-Ice.

https://github.com/tinyfpga/TinyFPGA-Bootloader
https://github.com/lawrie/tiny_usb_examples
https://github.com/davidthings/tinyfpga_bx_usbserial

See mecrisp-ice-1.9/common-verilog/usb. It's a drop-in UART core with the usual interface:

module usb_uart (
  input clk_48mhz,
  input resetq,
  output host_presence,

  // USB pins
  inout  pin_usb_p,
  inout  pin_usb_n,

  // UART interface
  input  uart_wr,
  input  uart_rd,
  input  [7:0] uart_tx_data,
  output [7:0] uart_rx_data,
  output uart_busy,
  output uart_valid
);

Matthias

[BrunoLevy]

Hi Matthias,
Awesome ! I'll try it asap !

[Mecrisp]

We are working on it:
ulixxe/usb_cdc#1

[Mecrisp]

Hi Bruno,
this one works perfectly now: https://github.com/ulixxe/usb_cdc
I already have ported Mecrisp-Ice (my Swapforth/J1a descendant) to the FOMU using the @ulixxe code for terminal, and I can recommend it.
Matthias

[Mecrisp]

Bonus points for allowing different clocks for USB and for the rest of the logic. Furthermore, it is very compact and it does not need any BRAM blocks.

[Mecrisp]

See https://github.com/ulixxe/usb_cdc, included here for a complete example:

https://sourceforge.net/projects/mecrisp/files/mecrisp-ice-2.2.tar.gz/download

mecrisp-ice-2.2/fomu/icestorm/j1a.v
mecrisp-ice-2.2/common-verilog/usb_cdc/

Done :-)

[Mecrisp]

  // ######   USB-CDC terminal   ##############################

  assign usb_dp_pu = resetq;

  wire usb_p_tx;
  wire usb_n_tx;
  wire usb_p_rx;
  wire usb_n_rx;
  wire usb_tx_en;

   SB_IO #(
       .PIN_TYPE(6'b 1010_01), // PIN_OUTPUT_TRISTATE - PIN_INPUT
       .PULLUP(1'b 0)
   ) iobuf_usbp (
       .PACKAGE_PIN(usb_dp),
       .OUTPUT_ENABLE(usb_tx_en),
       .D_OUT_0(usb_p_tx),
       .D_IN_0(usb_p_rx)
   );

   SB_IO #(
       .PIN_TYPE(6'b 1010_01), // PIN_OUTPUT_TRISTATE - PIN_INPUT
       .PULLUP(1'b 0)
   ) iobuf_usbn (
       .PACKAGE_PIN(usb_dn),
       .OUTPUT_ENABLE(usb_tx_en),
       .D_OUT_0(usb_n_tx),
       .D_IN_0(usb_n_rx)
   );

  usb_cdc #(.VENDORID(16'h0483), .PRODUCTID(16'h5740), .BIT_SAMPLES(4), .USE_APP_CLK(1), .APP_CLK_RATIO(4)) _terminal
  (
    // Part running on 48 MHz:

    .clk_i(clk_usb),
    .tx_en_o(usb_tx_en),
    .tx_dp_o(usb_p_tx),
    .tx_dn_o(usb_n_tx),
    .rx_dp_i(usb_p_rx),
    .rx_dn_i(usb_n_rx),

    // Part running on 12 MHz:

    .app_clk_i(clk),
    .rstn_i(resetq),

    .out_data_o(terminal_data),
    .out_valid_o(terminal_valid),
    .out_ready_i(terminal_rd),

    .in_data_i(io_dout[7:0]),
    .in_ready_o(terminal_ready),
    .in_valid_i(terminal_wr)
  );

  wire terminal_valid, terminal_ready;
  wire [7:0] terminal_data;
  wire terminal_wr = io_wr & io_addr[12];
  wire terminal_rd = io_rd & io_addr[12];