From e44a0734ddd590daf0d2490f31c8f98caa1af2cd Mon Sep 17 00:00:00 2001
From: Steven Hugg <hugg@fasterlight.com>
Date: Sun, 27 Jan 2019 14:47:03 -0500
Subject: [PATCH] verilog-vga

---
 doc/notes.txt                          |  2 +
 presets/verilog-vga/hvsync_generator.v | 69 ++++++++++++++++++++++
 presets/verilog-vga/lfsr.v             | 31 ++++++++++
 presets/verilog-vga/ram.v              | 80 ++++++++++++++++++++++++++
 presets/verilog-vga/test_hvsync.v      | 32 +++++++++++
 src/platform/verilog.ts                | 24 ++++----
 6 files changed, 228 insertions(+), 10 deletions(-)
 create mode 100644 presets/verilog-vga/hvsync_generator.v
 create mode 100644 presets/verilog-vga/lfsr.v
 create mode 100644 presets/verilog-vga/ram.v
 create mode 100644 presets/verilog-vga/test_hvsync.v

diff --git a/doc/notes.txt b/doc/notes.txt
index 14487f51..e6576b6b 100644
--- a/doc/notes.txt
+++ b/doc/notes.txt
@@ -91,6 +91,8 @@ TODO:
 - Safari: scope doesn't show while CRT in use
 - recording video indicator
 - verilog: support VGA/multisync monitor?
+- stego shareable images (http://pico-8.wikia.com/wiki/P8PNGFileFormat)
+- https://makecode.com/language?
 
 
 WEB WORKER FORMAT
diff --git a/presets/verilog-vga/hvsync_generator.v b/presets/verilog-vga/hvsync_generator.v
new file mode 100644
index 00000000..24587616
--- /dev/null
+++ b/presets/verilog-vga/hvsync_generator.v
@@ -0,0 +1,69 @@
+
+`ifndef HVSYNC_GENERATOR_H
+`define HVSYNC_GENERATOR_H
+
+/*
+Video sync generator, used to drive a simulated CRT.
+To use:
+- Wire the hsync and vsync signals to top level outputs
+- Add a 3-bit (or more) "rgb" output to the top level
+*/
+
+module hvsync_generator(clk, reset, hsync, vsync, display_on, hpos, vpos);
+
+  input clk;
+  input reset;
+  output reg hsync, vsync;
+  output display_on;
+  output reg [8:0] hpos;
+  output reg [8:0] vpos;
+
+  // declarations for TV-simulator sync parameters
+  // horizontal constants
+  parameter H_DISPLAY       = 256; // horizontal display width
+  parameter H_BACK          =  23; // horizontal left border (back porch)
+  parameter H_FRONT         =   7; // horizontal right border (front porch)
+  parameter H_SYNC          =  23; // horizontal sync width
+  // vertical constants
+  parameter V_DISPLAY       = 240; // vertical display height
+  parameter V_TOP           =   5; // vertical top border
+  parameter V_BOTTOM        =  14; // vertical bottom border
+  parameter V_SYNC          =   3; // vertical sync # lines
+  // derived constants
+  parameter H_SYNC_START    = H_DISPLAY + H_FRONT;
+  parameter H_SYNC_END      = H_DISPLAY + H_FRONT + H_SYNC - 1;
+  parameter H_MAX           = H_DISPLAY + H_BACK + H_FRONT + H_SYNC - 1;
+  parameter V_SYNC_START    = V_DISPLAY + V_BOTTOM;
+  parameter V_SYNC_END      = V_DISPLAY + V_BOTTOM + V_SYNC - 1;
+  parameter V_MAX           = V_DISPLAY + V_TOP + V_BOTTOM + V_SYNC - 1;
+
+  wire hmaxxed = (hpos == H_MAX) || reset;	// set when hpos is maximum
+  wire vmaxxed = (vpos == V_MAX) || reset;	// set when vpos is maximum
+  
+  // horizontal position counter
+  always @(posedge clk)
+  begin
+    hsync <= (hpos>=H_SYNC_START && hpos<=H_SYNC_END);
+    if(hmaxxed)
+      hpos <= 0;
+    else
+      hpos <= hpos + 1;
+  end
+
+  // vertical position counter
+  always @(posedge clk)
+  begin
+    vsync <= (vpos>=V_SYNC_START && vpos<=V_SYNC_END);
+    if(hmaxxed)
+      if (vmaxxed)
+        vpos <= 0;
+      else
+        vpos <= vpos + 1;
+  end
+  
+  // display_on is set when beam is in "safe" visible frame
+  assign display_on = (hpos<H_DISPLAY) && (vpos<V_DISPLAY);
+
+endmodule
+
+`endif
diff --git a/presets/verilog-vga/lfsr.v b/presets/verilog-vga/lfsr.v
new file mode 100644
index 00000000..c2f97ebb
--- /dev/null
+++ b/presets/verilog-vga/lfsr.v
@@ -0,0 +1,31 @@
+
+`ifndef LFSR_V
+`define LFSR_V
+
+/*
+Configurable Linear Feedback Shift Register.
+*/
+
+module LFSR(clk, reset, enable, lfsr);
+  
+  parameter TAPS   = 8'b11101;	// bitmask for taps
+  parameter INVERT = 0;		// invert feedback bit?
+  localparam NBITS  = $size(TAPS); // bit width (derived from TAPS)
+  
+  input clk, reset;
+  input enable;			// only perform shift when enable=1
+  output reg [NBITS-1:0] lfsr;  // shift register
+
+  wire feedback = lfsr[NBITS-1] ^ INVERT;
+
+  always @(posedge clk)
+  begin
+    if (reset)
+      lfsr <= {lfsr[NBITS-2:0], 1'b1}; // reset loads with all 1s
+    else if (enable)
+      lfsr <= {lfsr[NBITS-2:0], 1'b0} ^ (feedback ? TAPS : 0);
+  end
+
+endmodule
+
+`endif
diff --git a/presets/verilog-vga/ram.v b/presets/verilog-vga/ram.v
new file mode 100644
index 00000000..26f04d24
--- /dev/null
+++ b/presets/verilog-vga/ram.v
@@ -0,0 +1,80 @@
+
+`ifndef RAM_H
+`define RAM_H
+
+/*
+RAM_sync - Synchronous RAM module.
+RAM_async - Asynchronous RAM module.
+RAM_async_tristate - Async RAM module with bidirectional data bus.
+
+Module parameters:
+
+A - number of address bits (default = 10)
+D - number of data bits (default = 8)
+*/
+
+module RAM_sync(clk, addr, din, dout, we);
+  
+  parameter A = 10; // # of address bits
+  parameter D = 8;  // # of data bits
+  
+  input  clk;		// clock
+  input  [A-1:0] addr;	// address
+  input  [D-1:0] din;	// data input
+  output [D-1:0] dout;	// data output
+  input  we;		// write enable
+  
+  reg [D-1:0] mem [0:(1<<A)-1]; // (1<<A)xD bit memory
+  
+  always @(posedge clk) begin
+    if (we)		// if write enabled
+      mem[addr] <= din;	// write memory from din
+    dout <= mem[addr];	// read memory to dout (sync)
+  end
+
+endmodule
+
+module RAM_async(clk, addr, din, dout, we);
+  
+  parameter A = 10; // # of address bits
+  parameter D = 8;  // # of data bits
+  
+  input  clk;		// clock
+  input  [A-1:0] addr;	// address
+  input  [D-1:0] din;	// data input
+  output [D-1:0] dout;	// data output
+  input  we;		// write enable
+  
+  reg [D-1:0] mem [0:(1<<A)-1]; // (1<<A)xD bit memory
+  
+  always @(posedge clk) begin
+    if (we)		// if write enabled
+      mem[addr] <= din;	// write memory from din
+  end
+
+  assign dout = mem[addr]; // read memory to dout (async)
+
+endmodule
+
+module RAM_async_tristate(clk, addr, data, we);
+  
+  parameter A = 10; // # of address bits
+  parameter D = 8;  // # of data bits
+  
+  input  clk;		// clock
+  input  [A-1:0] addr;	// address
+  inout  [D-1:0] data;	// data in/out
+  input  we;		// write enable
+  
+  reg [D-1:0] mem [0:(1<<A)-1]; // (1<<A)xD bit memory
+  
+  always @(posedge clk) begin
+    if (we)		 // if write enabled
+      mem[addr] <= data; // write memory from data
+  end
+
+  assign data = !we ? mem[addr] : {D{1'bz}}; // read memory to data (async)
+
+endmodule
+
+`endif
diff --git a/presets/verilog-vga/test_hvsync.v b/presets/verilog-vga/test_hvsync.v
new file mode 100644
index 00000000..a3445ce8
--- /dev/null
+++ b/presets/verilog-vga/test_hvsync.v
@@ -0,0 +1,32 @@
+
+`include "hvsync_generator.v"
+
+/*
+A simple test pattern using the hvsync_generator module.
+*/
+
+module test_hvsync_top(clk, reset, hsync, vsync, rgb);
+
+  input clk, reset;
+  output hsync, vsync;
+  output [2:0] rgb;
+  wire display_on;
+  wire [8:0] hpos;
+  wire [8:0] vpos;
+
+  hvsync_generator hvsync_gen(
+    .clk(clk),
+    .reset(0),
+    .hsync(hsync),
+    .vsync(vsync),
+    .display_on(display_on),
+    .hpos(hpos),
+    .vpos(vpos)
+  );
+
+  wire r = display_on && (((hpos&7)==0) || ((vpos&7)==0));
+  wire g = display_on && vpos[4];
+  wire b = display_on && hpos[4];
+  assign rgb = {b,g,r};
+
+endmodule
diff --git a/src/platform/verilog.ts b/src/platform/verilog.ts
index d233c621..b77ecd6e 100644
--- a/src/platform/verilog.ts
+++ b/src/platform/verilog.ts
@@ -295,7 +295,7 @@ var VerilogPlatform = function(mainElement, options) {
     ctx.fillText(txt, x, y);
     ctx.shadowOffsetX = 0;
   }
-
+  
   // inner Platform class
     
  class _VerilogPlatform extends BasePlatform implements WaveformProvider {
@@ -308,6 +308,13 @@ var VerilogPlatform = function(mainElement, options) {
 
   getPresets() { return VERILOG_PRESETS; }
 
+  setVideoParams(width:number, height:number, clock:number) {
+    videoWidth = width;
+    videoHeight = height;
+    cyclesPerFrame = clock;
+    maxVideoLines = height+40;
+  }
+
   start() {
     video = new RasterVideo(mainElement,videoWidth,videoHeight,{overscan:true});
     video.create();
@@ -751,24 +758,21 @@ var VerilogPlatform = function(mainElement, options) {
 
 ////////////////
 
-var VERILOG_SIM_PRESETS = [
-  {id:'clock_divider.v', name:'Clock Divider'},
-  {id:'lfsr.v', name:'Linear Feedback Shift Register'},
+var VERILOG_VGA_PRESETS = [
   {id:'hvsync_generator.v', name:'Video Sync Generator'},
   {id:'test_hvsync.v', name:'Test Pattern'},
-  {id:'starfield.v', name:'Scrolling Starfield'},
-  {id:'chardisplay.v', name:'RAM Text Display'},
-  {id:'sound_generator.v', name:'Sound Generator'},
 ];
 
 
-var VerilogSimulatorPlatform = function(mainElement, options) {
+var VerilogVGAPlatform = function(mainElement, options) {
   this.__proto__ = new (VerilogPlatform as any)(mainElement, options);
 
-  this.getPresets = function() { return VERILOG_SIM_PRESETS; }
+  this.getPresets = function() { return VERILOG_VGA_PRESETS; }
+
+  this.setVideoParams(800-64, 520, 25000000);
 }
 
 ////////////////
 
 PLATFORMS['verilog'] = VerilogPlatform;
-PLATFORMS['verilog.sim'] = VerilogSimulatorPlatform;
+PLATFORMS['verilog-vga'] = VerilogVGAPlatform;