Implemented failsafe options at boot and inside menus for enabling/disabling serial, spkmodem and gfxterm

config/grub/config/grub.cfg

@@ -14,17 +14,36 @@ terminal_input --append at_keyboard
 terminal_input --append usb_keyboard
 terminal_output --append cbmemc
 
-gfxpayload=keep
-terminal_output --append gfxterm
+# User interface overrides wherever "keystatus" is supported
+# Keep SHIFT key pressed before powering on to disable graphics
+if keystatus --shift; then
+	terminal_output --append vga_text
+else
+	gfxpayload=keep
+	terminal_output --append gfxterm
 
-if [ -f (cbfsdisk)/background.png ]; then
-	insmod png
-	background_image (cbfsdisk)/background.png
-elif [ -f (cbfsdisk)/background.jpg ]; then
-	insmod jpeg
-	background_image (cbfsdisk)/background.jpg
+	if [ -f (cbfsdisk)/background.png ]; then
+		insmod png
+		background_image (cbfsdisk)/background.png
+	elif [ -f (cbfsdisk)/background.jpg ]; then
+		insmod jpeg
+		background_image (cbfsdisk)/background.jpg
+	fi
 fi
 
+# Keep CTRL pressed to enable default serial terminal (COM1 or the like)
+if keystatus --ctrl; then
+	serial
+	terminal_input --append serial
+	terminal_output --append serial
+fi
+
+# Keep ALT pressed to enable spkmodem
+if keystatus --alt; then
+	terminal_output --append spkmodem
+fi
+
+
 set default="0"
 if [ -f (cbfsdisk)/timeout.cfg ]; then
 	source (cbfsdisk)/timeout.cfg
@@ -198,3 +217,33 @@ menuentry 'Load MemTest86+  [m]' --hotkey='m' {
 	chainloader /img/memtest
 }
 fi
+
+submenu 'Other  [z]' --hotkey='z' {
+	menuentry 'Enable default serial terminal  [s]' --hotkey='s'  {
+		serial
+		terminal_input --append serial
+		terminal_output --append serial
+	}
+
+	menuentry 'Disable default serial terminal' {
+		terminal_input --remove serial
+		terminal_output --remove serial
+	}
+
+	menuentry 'Enable gfxterm' {
+		terminal_output --append gfxterm
+		terminal_output --remove vga_text
+	}
+	menuentry 'Disable gfxterm  [g]' --hotkey='g'  {
+		terminal_output --remove gfxterm
+		terminal_output --append vga_text
+	}
+
+	menuentry 'Enable spkmodem  [a]' --hotkey='a' {
+		terminal_output --append spkmodem
+	}
+
+	menuentry 'Disable spkmodem  [z]' --hotkey='z' {
+		terminal_output --remove spkmodem
+	}
+}