Implement basic ascii framebuffer (read only for now)

font_rom.vhd

@@ -0,0 +1,87 @@
+library ieee;
+
+use ieee.std_logic_1164.all;
+use ieee.std_logic_unsigned.all;
+use ieee.numeric_std.all;
+
+use std.textio.all;
+use ieee.std_logic_textio.all;
+
+entity font_rom is
+    generic (
+        input_clk: integer
+    );
+    port (
+        clk: in std_logic;
+        x, y: in std_logic_vector(9 downto 0);
+
+        rgb: out std_logic_vector(23 downto 0)
+    );
+end font_rom;
+
+architecture logic of font_rom is
+    type rom_type is array(0 to 127) of std_logic_vector(63 downto 0);
+    type framebuffer_type is array(0 to 59, 0 to 79) of std_logic_vector(7 downto 0);
+
+    impure function read_font(filename: in string) return rom_type is
+        file rom_file: text is in filename;
+        variable rom_line: line;
+        variable rom: rom_type;
+    begin
+        -- skip comment in first line
+        readline(rom_file, rom_line);
+
+        for i in rom_type'range loop
+            readline(rom_file, rom_line);
+            hread(rom_line, rom(i));
+        end loop;
+
+        return rom;
+    end function;
+
+    constant font: rom_type := read_font("font.hex");
+
+    constant framebuffer: framebuffer_type := (
+        0 => (x"48", x"61", x"6C", x"6c", x"6f", others => x"00"),
+        1 to 59 => (others => x"00")
+    );
+
+    signal char_x: integer range 0 to 79;
+    signal char_y: integer range 0 to 59;
+    signal current_char: std_logic_vector(7 downto 0);
+
+    signal current_glyph: std_logic_vector(63 downto 0);
+    signal current_glyph_pos: integer range 0 to 127;
+
+    signal glyph_pos_raw: std_logic_vector(5 downto 0);
+    signal glyph_pos: integer range 0 to 63;
+begin
+
+    char_x <= to_integer(unsigned(x(9 downto 3)));
+    char_y <= to_integer(unsigned(y(9 downto 3)));
+
+    process(clk) is
+    begin
+        if rising_edge(clk) then
+            current_char <= framebuffer(char_y, char_x);
+        end if;
+    end process;
+
+    current_glyph_pos <= to_integer(unsigned(current_char));
+
+    process(clk) is
+    begin
+        if rising_edge(clk) then
+            current_glyph <= font(current_glyph_pos);
+        end if;
+    end process;
+
+    glyph_pos_raw <= y(2 downto 0) & x(2 downto 0);
+    glyph_pos <= to_integer(unsigned(glyph_pos_raw));
+
+    -- actually currently BRG
+    rgb <=
+        "111111111111111111111111" when current_glyph(glyph_pos) = '1' else
+        "000000000000000000000000";
+
+end logic;