Add LTC frame format

Author: sam210723

sim/ltc/top.v

@@ -3,9 +3,41 @@ module top(
     output wire ltc
 );
 
-    parameter FPS = 25;
-    reg [79:0] frame;   // LTC frame
-    reg        out;     // Output buffer
+    /*
+     *  SMPTE 12M Linear Timecode (LTC) Frame Format
+     *  https://en.wikipedia.org/wiki/Linear_timecode#Longitudinal_timecode_data_format
+     *  
+     *  OFFSET  LEN  USE
+     *  0x00    4    Frame (units)
+     *  0x04    4    User Field 1
+     *  0x08    2    Frame (tens)
+     *  0x0A    1    Drop Frame Flag
+     *  0x0B    1    Color Frame Flag
+     *  0x0C    4    User Field 2
+     *  0x10    4    Seconds (units)
+     *  0x14    4    User Field 3
+     *  0x18    3    Seconds (tens)
+     *  0x1B    1    FLAG
+     *  0x1C    4    User Field 4
+     *  0x20    4    Minutes (units)
+     *  0x24    4    User Field 5
+     *  0x28    3    Minutes (tens)
+     *  0x2B    1    FLAG
+     *  0x2C    4    User Field 6
+     *  0x30    4    Hours (units)
+     *  0x34    4    User Field 7
+     *  0x38    2    Hours (tens)
+     *  0x3A    1    Binary Group Flag 1 (External Sync Source Flag)
+     *  0x3B    1    FLAG
+     *  0x3C    4    User Field 8
+     */
+
+    parameter FPS = 25;     // Frames per second
+    parameter CLK = 25e6;   // Clock frequency in Hz
+
+    reg [15:0] sync = 16'b0011111111111101;     // SMPTE 12M Sync Word
+    reg [79:0] frame;
+    reg        out;
 
     wire rst_n;
     crg reset(clk, rst_n);