From 227dce66e968e7580b5540f8556ca27ee0e349bc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Klemens=20Sch=C3=B6lhorn?= <klemens@schoelhorn.eu>
Date: Mon, 4 Jun 2018 15:47:58 +0200
Subject: [PATCH] Implement backspace control character

---
 terminal.vhd | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/terminal.vhd b/terminal.vhd
index 745dcf8..854ad20 100644
--- a/terminal.vhd
+++ b/terminal.vhd
@@ -52,6 +52,7 @@ begin
     -- the current row before jumping to the next one
     process(sys_clk)
         variable next_line: unsigned(5 downto 0);
+        variable previous_col: unsigned(6 downto 0);
     begin
         if rising_edge(sys_clk) then
             -- we write to the current cursor position and simply pass the data
@@ -74,9 +75,20 @@ begin
                 next_line := cursor_row + 1;
             end if;
 
+            -- calculate previous column (saturating)
+            if cursor_col = 0  then
+                previous_col := (others => '0');
+            else
+                previous_col := cursor_col - 1;
+            end if;
+
             if write_enable = '1' then
+                -- backspace
+                if write_data = x"08" then
+                    cursor_col <= previous_col;
+
                 -- carriage return
-                if write_data = x"0d" then
+                elsif write_data = x"0d" then
                     cursor_col <= (others => '0');
 
                 -- line feed (implicit CR)