GPIB: Cool, It Works with Linux!

Gambling is a way of life with computers. The technology is changing daily, and anyone involved with system administration should try to keep up with it at any cost. Sometimes it's all too much. You are asked whether a new feature can be introduced into the network. If you say no, you might fall behind the competition; if you say yes, you're bluffing and you might be shooting yourself in the foot. Linux became my most loved operating system, when I realized that saying yes is usually more gambling with a good chance of success, than bluffing with an empty hand. My involvement in GPIB for Linux is such a case.

GPIB is a standard bus in data acquisition and industrial process control. It was developed in 1965 by Hewlett-Packard and was first called HPIB. It was subsequently renamed GPIB (general purpose interface bus) or the IEEE488 interface. GPIB hardware is available everywhere. All kinds of AD converters, digital meters, even printers and plotters use it as the bus of choice. Clean up those dusty corners in laboratories, and you may find an ancient piece of hardware with a GPIB interface at the back. As PCs arrived on researchers' desks, GPIB interface boards were developed, enabling control of GPIB hardware chains via a computer.

I am involved with the Laboratory for Technical Physics in the Faculty for Mechanical Engineering in Ljubljana, capital of Slovenia. The staff uses GPIB for experimental control and data acquisition, and any computing environment introduced into the lab must support GPIB if at all possible. After I converted the laboratory to Linux, an end was put to printing via floppy disks and waiting in queues for the daily mail on the single computer hooked to the Internet. Standard Linux applications replaced most of the everyday software previously in use. However, GPIB support soon became an issue. I was not really a GPIB freak myself, but I knew about its wide use, and I knew the spirit of Linux from my long-time experience with it. The dice were rolling as I assured everyone, “GPIB for Linux? Yes, of course!” All I had in hand at the time was a short note in the Linux Hardware HOW-TO, directing me to the Linux Lab Project in Germany (see Resources).

On one fine web surfing day, I found what I needed: The Linux GPIB package, written by Claus Schroter at Freie Universitet, Berlin. The package includes a loadable GPIB driver module, the basic library for accessing the bus functions from C and a Tcl interface, enabling GPIB for the Tcl language.

I had Slackware 3.1, with kernel version 2.0.0 on a 100MHz Pentium board with 16MB RAM. The GPIB interface card available was the CEC PC488. A rather low-end ISA board but good enough for my testing purposes. Informative documentation of the package states that the following boards are supported: National Instruments AT-GPIB, NI PCII and PCIIa and compatible boards, IBM GPIB adapter, HP82355 and HP27109 adapters.

The module and GPIB library compiled out of the box, and after actually reading the README file, Tcl support compiled as well. The driver module can be configured at compile time, at module load time or via library calls. Necessary parameters are the hardware address of the GPIB board, the DMA channel and the IRQ being used.

Before use, the library must be configured as well using the /etc/gpib.conf file by default. A specific configuration can be done for every hardware device attached to the bus. A special identifier name should be provided for each device so that the library can access any hardware device by a reasonable name. I found this method of configuration very convenient. All GPIB devices on the bus have different addresses and their initialization strings vary. With configuration via /etc/gpib.conf file, the necessary parameters must be determined and written into the configuration file only once. Then, all you need to do is remember the arbitrary name you assigned to that device. There is also a Tcl/Tk-based application called ibconf which simplifies maintaining the configuration file.

The feature that drew most of my attention was remote GPIB, rGPIB. It is a very cool option that enables computers without a GPIB board to access a GPIB board on a remote computer across a TCP/IP network. It is much cheaper than buying interface cards and much simpler than swapping one GPIB board between computers. Remote GPIB uses RPC (remote procedure calls) for communication between client and server, so the RPC portmapper must be up and running before the rGPIB server can be used.