Application note for turn on ttyS4 / ttyS5 in Linux kernel 2.6.x

If you connect the touch controller at COM5(ttyS4)/COM6(ttyS5) or higher,
 need make sure the following features have been enabled in the kernel configuration
 for the kernel 2.6.x (Example: Fedora Core 5)

  [*] Extended 8250/16550 serial driver options
  [*]   Support more than 4 legacy serial ports
  [*]   Support for sharing serial interrupts

These drivers will assign the /dev/ttyS4 and /dev/ttyS5 nodes to the COM5 and COM6 ports on the motherboard.
You need to download the kernel, choose the kernel configuration, rebuild kernel, and lunch new kernel.



The below are item descriptions:

  config SERIAL_8250_EXTENDED
	bool "Extended 8250/16550 serial driver options"
	depends on SERIAL_8250
	help
	  If you wish to use any non-standard features of the standard "dumb"
	  driver, say Y here. This includes HUB6 support, shared serial
	  interrupts, special multiport support, support for more than the
	  four COM 1/2/3/4 boards, etc.

	  Note that the answer to this question won't directly affect the
	  kernel: saying N will just cause the configurator to skip all
	  the questions about serial driver options. If unsure, say N.

  config SERIAL_8250_MANY_PORTS
	bool "Support more than 4 legacy serial ports"
	depends on SERIAL_8250_EXTENDED && !IA64
	help
	  Say Y here if you have dumb serial boards other than the four
	  standard COM 1/2/3/4 ports. This may happen if you have an AST
	  FourPort, Accent Async, Boca (read the Boca mini-HOWTO, available
	  from <http://www.tldp.org/docs.html#howto>), or other custom
	  serial port hardware which acts similar to standard serial port
	  hardware. If you only use the standard COM 1/2/3/4 ports, you can
	  say N here to save some memory. You can also say Y if you have an
	  "intelligent" multiport card such as Cyclades, Digiboards, etc.

  config SERIAL_8250_SHARE_IRQ
	bool "Support for sharing serial interrupts"
	depends on SERIAL_8250_EXTENDED
	help
	  Some serial boards have hardware support which allows multiple dumb
	  serial ports on the same board to share a single IRQ. To enable
	  support for this in the serial driver, say Y here.
