Correctly handle CR followed by LF

This would previously result in an empty line, because the CR resets the
current column to zero. Now we remember the last written char and column
so that we can restore the column before finishing the line.

terminal.vhd

@@ -46,6 +46,9 @@ architecture syn of terminal is
     signal rowlen_we: std_logic;
     signal rowlen_wa: std_logic_vector(5 downto 0);
     signal rowlen_di: std_logic_vector(6 downto 0);
+
+    signal last_written_char: std_logic_vector(7 downto 0);
+    signal last_cursor_col: unsigned(6 downto 0);
 begin
 
     -- writes the next character, advances the cursor and saves the length of
@@ -83,6 +86,10 @@ begin
             end if;
 
             if write_enable = '1' then
+                -- save last written char and column for correct CR, LF handling
+                last_written_char <= write_data;
+                last_cursor_col <= cursor_col;
+
                 -- backspace
                 if write_data = x"08" then
                     cursor_col <= previous_col;
@@ -97,6 +104,12 @@ begin
                     cursor_row <= next_line;
                     rowlen_we <= '1'; -- save row length
 
+                    -- write the row length with was valid before CR reset the
+                    -- cursor (for consecutive CR, LF)
+                    if last_written_char = x"0d" then
+                        rowlen_di <= std_logic_vector(last_cursor_col);
+                    end if;
+
                 -- normal characters
                 else
                     charbuf_we <= '1'; -- write normal characters