[HDL] Add digitial I/O with protection circuitry

HDL/common/digital_io_behavorial.v

@@ -0,0 +1,46 @@
+//-----------------------------------------------------
+// This file includes behavorial modeling 
+// for digital I/O cells
+// These cells may not be directly used for physical design
+// Synthesis tools may be needed
+//-----------------------------------------------------
+`timescale 1ns/1ps
+
+//-----------------------------------------------------
+// Function    : A minimum input pad
+//-----------------------------------------------------
+module GPIN (
+  inout A, // External PAD signal
+  output Y // Data input
+);
+  assign Y = A;
+endmodule
+
+//-----------------------------------------------------
+// Function    : A minimum output pad
+//-----------------------------------------------------
+module GPOUT (
+  inout Y, // External PAD signal
+  input A // Data output
+);
+  assign Y = A;
+endmodule
+
+//-----------------------------------------------------
+// Function    : A minimum embedded I/O
+//               just an overlay to interface other components
+//-----------------------------------------------------
+module EMBEDDED_IO (
+  input SOC_IN, // Input to drive the inpad signal
+  output SOC_OUT, // Output the outpad signal
+  output SOC_DIR, // Output the directionality
+  output FPGA_IN, // Input data to FPGA
+  input FPGA_OUT, // Output data from FPGA
+  input FPGA_DIR // direction control 
+);
+
+  assign FPGA_IN = SOC_IN;
+  assign SOC_OUT = FPGA_OUT;
+  assign SOC_DIR = FPGA_DIR;
+endmodule
+

HDL/common/digital_io_hd.v

@@ -1,57 +1,52 @@
 `timescale 1ns/1ps
 
-module GPIO (A, IE, OE, Y, in, out, mem_out);
-    output A;
-    output IE;
-    output OE;
-    output Y;
-    input in;
-    output out;
-    input mem_out;
-
-    assign A = in;
-    assign out = Y;
-    assign IE = mem_out;
-    sky130_fd_sc_hd__inv_1 ie_oe_inv (
-        .A	(mem_out),
-        .Y	(OE) );
-endmodule
-
 //-----------------------------------------------------
-// Function    : A minimum input pad
+// Function    : An embedded I/O with
+//               - An I/O isolation signal to set 
+//                 the I/O in input mode. This is to avoid
+//                 any unexpected output signals to damage
+//                 circuits outside the FPGA due to configurable
+//                 memories are not properly initialized
+//                 This feature may not be needed if the configurable
+//                 memory cell has a built-in set/reset functionality
+//               - Internal protection circuitry to ensure
+//                 clean signals at all the SOC I/O ports
+//                 This is to avoid 
+//                   - output any random signal
+//                     when the I/O is in input mode, also avoid
+//                   - driven by any random signal
+//                     when the I/O is output mode
+//
+// Note: This cell is built with Standard Cells from HD library
+//       It is already technology mapped and can be directly used
+//       for physical design
 //-----------------------------------------------------
-module GPIN (
-  inout A, // External PAD signal
-  output Y // Data input
-);
-  assign Y = A;
-endmodule
-
-//-----------------------------------------------------
-// Function    : A minimum output pad
-//-----------------------------------------------------
-module GPOUT (
-  inout Y, // External PAD signal
-  input A // Data output
-);
-  assign Y = A;
-endmodule
-
-//-----------------------------------------------------
-// Function    : A minimum embedded I/O
-//               just an overlay to interface other components
-//-----------------------------------------------------
-module EMBEDDED_IO (
-  input SOC_IN, // Input to drive the inpad signal
+module EMBEDDED_IO_HD (
+  input SOC_IN,   // Input to drive the inpad signal
   output SOC_OUT, // Output the outpad signal
   output SOC_DIR, // Output the directionality
   output FPGA_IN, // Input data to FPGA
   input FPGA_OUT, // Output data from FPGA
-  input FPGA_DIR // direction control 
+  input FPGA_DIR, // direction control 
+  input ISOL_N    // Isolation enable signal
 );
 
-  assign FPGA_IN = SOC_IN;
-  assign SOC_OUT = FPGA_OUT;
-  assign SOC_DIR = FPGA_DIR;
+  sky130_fd_sc_hd__and2_0 ISOL_EN_GATE (.A(ISOL_N),
+                                        .B(FPGA_DIR),
+                                        .X(SOC_DIR)
+                                       );
+  
+  // Use drive-strength 2 for a high fan-out from global routing architecture
+  sky130_fd_sc_hd__and2_2 IN_PROTECT_GATE (.A(SOC_DIR),
+                                           .B(SOC_IN),
+                                           .X(FPGA_IN)
+                                          );
+
+  // Use drive-strength 1 for a potential high fan-out from SoC components
+  sky130_fd_sc_hd__and2b_1 OUT_PROTECT_GATE (.A(SOC_DIR),
+                                             .B(FPGA_OUT),
+                                             .X(SOC_OUT)
+                                            );
+
 endmodule