initial verilog

.gitignore

@@ -2,3 +2,5 @@
 *.o
 *.bin
 build/*
+*.vcd
+*.out

Makefile

@@ -1,4 +1,9 @@
 
-NEXTPNR_FLAGS= --45k --package CABGA381 --speed 6 --freq 65
+
-YOSYS_FLAGS=
+
+
+.PHONY all clean test
+
+
+
 

groovylight/hub75.py

@@ -28,15 +28,11 @@ class Hub75Driver(Module):
         if base_freq // 2 > 30e6:
             raise RuntimeError("hi")
 
-        self.phase = Signal() # divider/counter
         self.addr = Signal(5)
         self.latch = Signal()
         self.output_en = Signal()
-        self.rgb = Signal(6, reset=0b111010)
+        color = Signal(24, reset=0xA0FF00)
-
+        self.rgb = Signal(6)
-
-        # clk-en acts as a gate.
-        clock_en = Signal()
  
         self.clock_out = Signal()
 
@@ -46,21 +42,34 @@ class Hub75Driver(Module):
 
         counter = Signal(32)
 
+        should_expose = (counter < (16 << bcm_value)) & (bcm_value != 0)
+
+
+        # this state both sets the OE low to drive the display with the previous frame
+        # while also loading the next row
+        # FIXME: there's a bug on the starting conditions right now, we are losing the lowest bit.
         fsm.act("WRITEROW",
-                self.output_en.eq(1),
+                self.output_en.eq(~should_expose),
-                If(counter < 256,
+                self.rgb[0].eq((color >> bcm_value) & 1),
+                self.rgb[3].eq((color >> bcm_value) & 1),
+                self.rgb[1].eq((color >> (bcm_value + 8)) & 1),
+                self.rgb[4].eq((color >> (bcm_value + 8)) & 1),
+                self.rgb[2].eq((color >> (bcm_value + 16)) & 1),
+                self.rgb[5].eq((color >> (bcm_value + 16)) & 1),
+
+                NextValue(counter, counter + 1),
+                If(counter < linedepth * 2,
                     self.clock_out.eq(counter[0]),
-                    NextValue(counter, counter + 1),
+                ),
-                    If(counter[0], NextValue(self.rgb, self.rgb + 3)),
+                If(~(counter < linedepth * 2) & ~should_expose,
-                ).Else(
                     NextValue(counter, 0),
-                    NextState("EXPOSE"),
+                    NextState("LATCH"),
                 ),
         )
 
         fsm.act("EXPOSE",
                 self.output_en.eq(0),
-                If(counter < (1000 << bcm_value),
+                If(counter < (16 << bcm_value),
                    NextValue(counter, counter + 1),
                 ).Else(
                     NextValue(counter, 0),
@@ -70,52 +79,14 @@ class Hub75Driver(Module):
 
         fsm.act("LATCH",
                 self.latch.eq(1),
+                self.output_en.eq(1),
                 NextValue(counter, 0),
                 If(bcm_value == 7,
                     NextValue(bcm_value, 0),
                     NextValue(self.addr, self.addr + 1),
-                ).Else(NextValue(bcm_value, 1)),
+                ).Else(
+                    NextValue(bcm_value, bcm_value + 1),
+                ),
                 
                 NextState("WRITEROW"),
         )
-
-
-        # fsm.act("ready",
-        #         NextValue(self.output_en, 1),
-        #         NextValue(self.pixnum, linedepth - 1),
-        #         NextValue(self.latch, 0),
-        #         If(self.phase == 1,
-        #            NextValue(self.addr, self.addr + 1),
-        #            NextValue(clock_en, 1),
-        #            NextState("transmit"),
-        #         ),
-        #         # If((self.state_count == 7), NextValue(clock_en, ~clock_en)),
-        # )
-        # fsm.act("transmit",
-        #     If(self.phase == 1,
-        #         NextValue(self.pixnum, self.pixnum - 1),
-        #         If(self.pixnum == 0,
-        #            NextState("latch_delay"),
-        #         )
-        #     )
-        # )
-        # fsm.act("latch_delay",
-        #     NextValue(clock_en, 0),
-        #         If(self.phase == 1,
-        #            NextState("latchout")
-        #            )
-        #         )
-        # fsm.act("latchout",
-        #     If(self.phase == 1,
-        #        NextValue(self.latch, 1),
-        #        NextValue(counter, 0),
-        #        NextState("done")
-        #     )
-        # )
-        # fsm.act("done",
-        #     NextValue(self.output_en, 0),
-        #     NextValue(self.latch, 0),
-        #     NextValue(counter, counter + 1),
-        #     If(counter == 255, NextState("ready"))
-        # )
-        #

verilog/hub75e.sv

@@ -0,0 +1,125 @@
+module hub75e (
+    input clk,
+    input write_trig,
+    input [1:0][BIT_DEPTH - 1:0] rgb_row[ROW_DEPTH],
+    output reg [4:0] addr,
+    output reg [2:0] panel_rgb0,
+    output reg [2:0] panel_rgb1,
+    output reg display_clk = 0,
+    output reg out_enable = 1,
+    output reg latch = 0,
+    output reg done = 0
+);
+
+  parameter integer ROW_DEPTH = 128, BIT_DEPTH = 8;
+
+  reg [31:0] counter = 0;
+  reg [ 3:0] bcm_shift = 7;  // which bit of the colors are we currently exposing.
+
+  localparam integer StateInit = 0;
+  localparam integer StateWriteRow = 1;
+  localparam integer StateLatchout = 2;
+  // the last data that we clock out for the row won't be exposed
+  // in the next writerow state because we'll change addresses.
+  localparam integer StateFinishExpose = 3;
+
+  reg [7:0] state = StateInit;  // our state
+
+
+  assign addr = 5'b10101;
+  assign panel_rgb0 = 3'b101;
+  assign panel_rgb1 = 3'b010;
+
+  // initial begin
+  //   state <= StateInit;
+  //   counter <= 0;
+  //   bcm_shift <= 7;
+  // end
+
+  // The FSM is a bit confusing since it's optimized for *speed*
+  // We can basically display the previous line of data while we write the
+  // next one. So instead of having WRITEROW -> LATCH -> EXPOSE
+  // like most modules do, we can instead do (WRITEROW + EXPOSE_PREV) -> LATCH
+  // There is an edge case for the first/last bits of the color depth.
+  // When we start writing a line, we can't flash anything since there's no
+  // previous. Likewise, when we end a line, we have to have an extra expose
+  // period since there is no next writerow for this address. As a result,
+  // we want to go MSB to LSB for our BCM so that the trailing expose time is
+  // short!
+
+  wire should_clock, should_expose;
+  assign should_clock  = counter < ROW_DEPTH * 2;
+  assign should_expose = (counter < (16 << bcm_shift + 1)) && (bcm_shift != 7);
+
+  always_ff @(posedge clk) begin
+    counter <= counter + 1;
+    case (state)
+      StateInit: begin
+        // wait for the signal to write out our lines.
+        if (write_trig) begin
+          bcm_shift <= 7;
+          counter <= 0;
+          done <= 0;
+          state <= StateWriteRow;
+        end
+      end
+
+      StateWriteRow: begin
+        if (should_clock) begin
+          // we have data to  clock
+          display_clk <= counter[0];
+          if (counter[0]) begin
+            // load the next pixel data. this is the falling edge since the
+            // previous value is 1.
+          end
+        end
+        if (should_expose) begin
+          // we are still in our expose state, and our bcm shift is not the
+          // first one, so we should expose.
+          out_enable <= 0;
+        end else begin
+          out_enable <= 1;
+        end
+        // if we're done with our data clock out and also done with exposing
+        // the previous frame, go next.
+        if (~should_clock && ~should_expose) begin
+          counter <= 0;
+          state   <= StateLatchout;
+        end
+      end
+
+      StateLatchout: begin
+        // raise latch high; compute next bcm.
+        latch <= 1;
+        out_enable <= 1;
+        counter <= counter + 1;
+        if (counter > 3) begin
+          if (bcm_shift == 0) begin
+            // done with the line. do the last (short) expose
+            state <= StateFinishExpose;
+            latch <= 0;
+          end else begin
+            bcm_shift <= bcm_shift - 1;
+            state <= StateWriteRow;
+            latch <= 0;
+          end
+        end
+      end
+
+      StateFinishExpose: begin
+        assert (bcm_shift == 0);
+        if (counter < (16 << bcm_shift)) begin
+          out_enable <= 0;
+        end else begin
+          out_enable <= 1;
+          state <= StateInit;
+          done <= 1;
+          // we are done!
+        end
+      end
+      default: begin
+      end
+    endcase
+  end
+
+endmodule

verilog/tb/hub75e_tb.sv

@@ -0,0 +1,48 @@
+`timescale 1ns / 100ps  // 1 ns time unit, 100 ps resolution
+module hub75e_tb;
+
+  reg clk;
+  reg write_trig;
+
+  reg [1:0][7:0] rgb_row[128];
+
+  wire [4:0] addr_out;
+  wire [2:0] rgb0;
+  wire [2:0] rgb1;
+  wire display_clk;
+  wire out_enable;
+  wire latch;
+  wire done;
+
+
+  hub75e dut (
+      .clk(clk),
+      .write_trig(write_trig),
+      .rgb_row(rgb_row),
+      .addr(addr_out),
+      .panel_rgb0(rgb0),
+      .panel_rgb1(rgb1),
+      .display_clk(display_clk),
+      .out_enable(out_enable),
+      .latch(latch),
+      .done(done)
+  );
+
+  always #5 clk = !clk;
+  initial begin
+    $dumpfile("wave.vcd");
+    $dumpvars(0, hub75e_tb);
+    clk = 0;
+    write_trig = 1;
+    repeat (2) @(posedge clk);
+    write_trig = 0;
+
+    @(done);
+    repeat (20) @(posedge clk);
+    $finish();
+  end
+  initial begin
+    repeat (100000) @(posedge clk);
+    $finish();
+  end
+endmodule