add support for in/out GPIO pins on ULX3S

The ULX3S has 2x28 IO pins that can be used either individually or as
differential pairs. Currently we're going to assume an individual setup (you can
configure their behaviour in the .lpf file).

The convention is to see them as gp[27] (GPIO positive) and gn[28] (GPIO
negative) arrays. This is how they're numbered on the board itself. To work with
this convention, we split out the GPIO address space into 0x00XX and 0x02XX for
setting in/output values of gp and gn pins respectively, and use 0x01XX and
0x3XX for setting the direction of the gn and gp pins.

We define pinModeGp and pinModeGn to set the pin direction. pinMode becomes an
alias for pinModeGn.

j1b/ulx3s/README.md

@@ -20,24 +20,53 @@ low-hanging fruit like GPIOs should follow shortly.
 
 PWR button resets the board
 
+
 memory map:
 
+0x00XX: gp GPIOs
+read/write
+either write bit to or read bit from address corresponding to the gp pin numbers
+on the board
+
+0x01XX: gp GPIO in/out direction
+read/write
+set direction of corresponding gp pin; 0 = input (default), 1 = output
+
+example:
+  $001b io@         \ read gn[27]
+  OUTPUT $011b io!  \ set direction of gn[27] to output
+  1 $001b io!       \ set gn[27] to high
+
+
+0x02XX: gn GPIOs
+read/write
+either write bit to or read bit from address corresponding to the gn pin numbers
+on the board
+
+0x03XX: gn GPIO in/out direction
+read/write
+set direction of corresponding gn pin; 0 = input (default), 1 = output
+
+example:
+  $021b io@         \ read gn[27]
+  OUTPUT $031b io!  \ set direction of gn[27] to output
+  1 $021b io!       \ set gn[27] to high
+
+
 0x0400: buttons (excluding PWR)
-direction: in
+read
 each button occupies one bit in the bottom 6 bits
 
 as per silkscreen labels on the board:
 |  32 - 6  |  5  |  4  |  3  |  2  |  1  |  0  |
  unused     RIGHT LEFT  DOWN  UP    F2    F1
 
 example:
-
   $0400 io@ .
 
 
-
 0x0404: leds
-direction: out
+write
 each led occupies one bit in the bottom 8 bits
 
 as per silkscreen labels on the board:
@@ -53,4 +82,3 @@ example:
     again
   ;
   led-counter
-

j1b/verilog/ulx3s_top.v

@@ -5,6 +5,8 @@ module ulx3s_top(
 
            input wire [6:0]  btn,
            output wire [7:0] led,
+           output wire [3:0] audio_l, audio_r, audio_v,
+           inout wire [27:0] gp, gn,
 
            input wire        ftdi_txd,
            output wire       ftdi_rxd,
@@ -95,6 +97,11 @@ module ulx3s_top(
     {io_wr_, io_rd_, mem_addr_, dout_} <= {io_wr, io_rd, mem_addr, dout};
 
   /*      READ            WRITE
+    00xx  GP rd           GP wr
+    01xx  GP direction    GP direction
+    02xx  GN rd           GN wr
+    03xx  GP direction    GN direction
+
     0400  buttons rd
     0404                  LEDs wr
 
@@ -111,31 +118,57 @@ module ulx3s_top(
 
   reg [63:0] counter_;
 
+  reg [27:0] gp_o;
+  wire [27:0] gp_i;
+  reg [27:0] gp_dir;   // 1:output, 0:input
+  reg [27:0] gn_o;
+  wire [27:0] gn_i;
+  reg [27:0] gn_dir;   // 1:output, 0:input
+
   always @(posedge fclk) begin
     casez (mem_addr)
-    16'h0400: din <= {27'd0, btn[6:1]};
+      16'h00??: din <= gp_i[mem_addr[6:0]];
+      16'h01??: din <= gp_dir[mem_addr[6:0]];
+      16'h02??: din <= gn_i[mem_addr[6:0]];
+      16'h03??: din <= gn_dir[mem_addr[6:0]];
 
-    16'h1000: din <= {24'd0, uart0_data};
-    16'h1008: din <= uart_baud;
-    16'h2000: din <= {30'd0, uart0_valid, !uart0_busy};
+      16'h0400: din <= {27'd0, btn[6:1]};
 
-    16'h1010: din <= MHZ * 1000000;
-    16'h1014: din <= counter_[31:0];
-    16'h1018: din <= counter_[63:32];
-    16'h101c: din <= ms;
+      16'h1000: din <= {24'd0, uart0_data};
+      16'h1008: din <= uart_baud;
+      16'h2000: din <= {30'd0, uart0_valid, !uart0_busy};
 
-    default:  din <= 32'bx;
+      16'h1010: din <= MHZ * 1000000;
+      16'h1014: din <= counter_[31:0];
+      16'h1018: din <= counter_[63:32];
+      16'h101c: din <= ms;
+
+      default:  din <= 32'bx;
     endcase
 
     if (io_wr_) begin
       casez (mem_addr_)
+        16'h00??: gp_o[mem_addr_[6:0]] <= dout_[0];
+        16'h01??: gp_dir[mem_addr_[6:0]] <= dout_[0];
+        16'h02??: gn_o[mem_addr_[6:0]] <= dout_[0];
+        16'h03??: gn_dir[mem_addr_[6:0]] <= dout_[0];
+
         16'h0404: led <= dout_;
+
         16'h1008: uart_baud <= dout_;
         16'h1010: counter_ <= counter;
       endcase
     end
   end
 
+  genvar i;
+  for (i = 0; i <= 27; i = i + 1) begin
+    assign gp[i] = gp_dir[i] ? gp_o[i] : 1'bz;
+    assign gp_i[i] = gp[i];
+    assign gn[i] = gn_dir[i] ? gn_o[i] : 1'bz;
+    assign gn_i[i] = gn[i];
+  end
+
   assign uart0_wr = io_wr_ & (mem_addr_ == 16'h1000);
   assign uart0_rd = io_rd_ & (mem_addr_ == 16'h1000);