Add documentation to VGA interface

diff --git a/libraries/vga/vga_counter.vhd b/libraries/vga/vga_counter.vhd
index 907188ed1460e28a616dcdef653e106dc1921026..8f3d40005cefc0bf98a64c38bdaa5de75a88bf0c 100644 (file)
--- a/libraries/vga/vga_counter.vhd
+++ b/libraries/vga/vga_counter.vhd
@@ -1,3 +1,7 @@
+--------------------------------------------------------------------------------
+-- vga_counter - pixel counter and sync generator for VGA interfaces
+--------------------------------------------------------------------------------
+
 library ieee;
 use ieee.std_logic_1164.all;
 use ieee.numeric_std.all;

diff --git a/libraries/vga/vga_tiler.vhd b/libraries/vga/vga_tiler.vhd
index ae4516055d55d0633fb1f3d98b296dcde3dc32d0..52225c065f542b575bc6ec218977d9f112b2fceb 100644 (file)
--- a/libraries/vga/vga_tiler.vhd
+++ b/libraries/vga/vga_tiler.vhd
@@ -1,3 +1,36 @@
+--------------------------------------------------------------------------------
+-- vga_tiler - tile-based graphics controller for VGA interfaces
+--------------------------------------------------------------------------------
+-- 0x0000 - 0x2000: Screen buffer
+--                  Each byte is an index into tile memory
+--                  Byte 0 is the top-left tile
+-- 0x2000 - 0x27ff: Tile data
+--                  Each tile is 8x8 pixels and consists of 8 bytes
+--                  The first byte of a tile is the top row, one pixel per bit
+--                  At startup, a subset of the Commodore64 font is loaded into
+--                  tile memory, mapped to appropriate ASCII characters
+--------------------------------------------------------------------------------
+-- WISHBONE DATASHEET
+--
+-- Wishbone specification used: Rev B.3
+-- Interface type: device
+-- Port size: 8-bit
+-- Operand sizes: 8-bit
+-- Endianness: undefined (port size same as granularity)
+-- Data transfer sequence: undefined
+-- Clock constraints: 50 MHz expected
+-- Signals:
+-- * rst_i
+-- * clk_i
+-- * cyc_i
+-- * stb_i
+-- * we_i
+-- * ack_o
+-- * adr_i (14-bit)
+-- * dat_i (8-bit)
+-- * dat_o (8-bit)
+--------------------------------------------------------------------------------
+
 library ieee;
 use ieee.std_logic_1164.all;
 use ieee.std_logic_misc.all;