I'm writing a kernel module for Linux v3.2 to control an external laser, but I'm having trouble communicating signals through the RS232 serial port on the machine. Buy audio test and measurement equipment here. RS232 lead, USB to serial. Connects an LA100 or a MiniSonic to a computer that doesn't have a serial port.

Serial HOWTO: Serial Port Devices /dev/ttyS2, etc. Common serial port names are /dev/ttyS0, /dev/ttyS1, etc.

Then around the year 2000 came the USB bus with names like /dev/ttyUSB0 and /dev/ttyACM1 (for the ACM modem on the USB bus). Multiport serial card used somewhat differnt names (depending on the brand) such as /dev/ttyE5.

Since DOS provided for 4 serial ports on the old ISA bus: COM1-COM4, or ttyS0-ttyS3 in Linux, most serial ports on the newer PCI bus used higher numbers such as ttyS4 or ttyS14 (prior to kernel 2. Net Collection Rate Definition. Skype Premium Download Softonic For Android. 6.13). But since most PCs only came with one or two serial ports, ttyS0 and possibly ttyS1 (for the second port) the PCI bus can now use ttyS2 (kernel 2.6.15 on). All this permits one to have both ISA serial ports and PCI serial ports on the same PC with no name conflicts. 0-1 (or 0-3) are reserved for the old ISA bus (or the newer LPC bus) and 2-upward (or 4-upward or 14-upward) are used for PCI, where older schemes are shown in parentheses. It's not required to be this way but it often is.

If you're using udev (which puts only the device you have on your computer into the /dev directory at boottime) then there's an easy way to change the device names by editing files in /etc/udev/. For example, to change the name of what the kernel detects as ttyS3 to what you want to name it: ttyS14, add a line similar to this to /etc/udev/udev.rules BUS=='pci' KERNEL=='ttyS3', NAME='ttyS14' On-board serial ports on motherboards which have both PCI and ISA slots are likely to still be ISA ports. Even for all-PCI-slot motherboards, the serial ports are often not PCI. Instead, they are either ISA, on an internal ISA bus or on a LPC bus which is intended for slow legacy I/O devices: serial/parallel ports and floppy drives. Devices in Linux have major and minor numbers. The serial port ttySx (x=0,1,2, etc.) is major number 4.

You can see this (and the minor numbers too) by typing: 'ls -l ttyS*' in the /dev directory. To find the device names for various devices, see the 'devices' file in the kernel documentation. There formerly was a 'cua' name for each serial port and it behaved just a little differently. For example, ttyS2 would correspond to cua2. It was mainly used for modems.