GrasPiB

GPIB interface board for Raspberry Pi, designed to work with linux-gpib gpio bitbang driver. Extra features include: RS232 serial interface, voltage regulator, fan mount and I2C conector.

Features

• Active GPIB interface circuit using SN7516x bus driver ICs
• RS232 serial interface (MAX3232 level converter), with optionally configurable RTS and CTS lines
• Step down voltage regulator (LM2576) for use with higher voltage power supplies (7-35VDC)
• 25mm cooling fan mounting holes and 2pin JST-PH connector for power
• I2C break out connector with one extra GPIO line (5pin JST-PH connector)
• Stacks on top of a Raspberry Pi

Configuration options

JP7 Power supply selection:

• Close pins 1-2: Power from J5 screw terminal trough onboard regulator circuit (7-35VDC input)
• Close pins 2-3: Power from J5 screw terminal bypassing onboard regulator circuit (5VDC input only !!)
• Leave Open: Power from Raspberry Pi power input USB connector, GrasPiB regulator circuit is isolated

JP6 Output Voltage select on I2C breakout connector

• Close pins 1-2: 3,3V on J4 pin 1
• Close pins 2-3: 5V on J4 pin 1

Enabling RS232 CTS and RTS lines:

• Close jumpers JP1, JP2, JP4 and JP5, open JP3 positions 1-2 and close positions 2-3
• This change also needs the GPIB DIO3 signal to be reassigned from GPIO16 to GPIO21 (linux-gpib driver code modifications needed)

Linux-gpib setup instructions

(following instructions were tested on a fresh Raspberry Pi OS Lite image)

0. Setup and configure OS on Raspberry Pi

   • Do as you would with a fresh OS image (passwords, networking, services, communication ports...)

1. Install build tools and dependencies

   • Build tools: $ sudo apt install build-essential autoconf automake libtool flex bison
   • RPi kernel headers: $ sudo apt install raspberrypi-kernel-headers
   • Python3 headers: $ sudo apt install python3-dev

2. Download linux-gpib source files

   • Get release archives (4.3.4 or later) from https://sourceforge.net/projects/linux-gpib/files
   • or get the latest source from https://sourceforge.net/p/linux-gpib/code/HEAD/tree/

3. Build and install kernel drivers

   • Enter linux-gpib-kernel directory $ cd linux-gpib-src-dir/linux-gpib-kernel
   • Build kernel module by running make $ make
   • Install kernel module $ sudo make install
   • Update kernel module list $ sudo depmod -a
   • Load gpib_bitbang kernel module $ sudo modprobe gpib_bitbang
   • Now there should be some gpib* devices in /dev
   • Make the module loads on boot by adding gpib_bitbang line to /etc/modules-load.d/modules.conf

When Raspberry Pi OS kernel gets upgraded, linux-gpib kernel module also needs to be rebuilt and reinstalled. Basically just repeat above make and make install steps when kernel gets upgraded...

4. Build and install user space tools

   • Enter linux-gpib-user directory: $ cd linux-gpib-src-dir/linux-gpib-user
   • If building from svn checkout first run bootstrap script: $ ./bootstrap
   • Run configure script: $ ./configure (run $ ./configure --help to list additional options)
   • Build user space tools by running make: $ make
   • Install user space tools: $ sudo make install
   • Make sure that shared library directory (default: /usr/local/lib/) is listed in: /etc/ld.so.conf.d/
   • Then run: $ sudo ldconfig

5. Configure GPIB interface

   • Open gpib.conf configuration file $ sudo nano /usr/local/etc/gpib.conf (default location)
   • Set board_type = "gpib_bitbang" and other relevant settings (for details refer to included gpib.conf file, linux-gpib documentetion and included template file linux-gpib-src-dir/linux-gpib-user/util/template/gpib.conf)
   • Run gpib_config so the driver reads the configuration file $ sudo gpib_config --minor 0
   • Make the last command execute on every startup using crontab entry:
     • Edit crontab for root user: $ sudo crontab -e
     • Add line the following line to cron tab file: @reboot /usr/local/sbin/gpib_config --minor 0

6. Enable non root users to use GPIB interface without sudo

   • Add new gpib system group: $ sudo groupadd -r gpib
   • Append your_user_name to gpib supplementary group: $ sudo usermod -a -G gpib your_user_name
   • Create /etc/udev/rules.d/99-gpib.rules file and add line: SUBSYSTEM=="gpib_common", GROUP="gpib", MODE="0660"
   • Reboot system to apply changes (udevadm utility can also be used, but reboot is dead simple to remember)
   • Test by running ibtest without sudo

Above instructions should result in an environment with a functional GPIB interface, C headers and python bindings, ready for use.

Enabling RS232 Hardware flow control

Hardware setup:

On the Raspberry Pi CTS and RTS signals are mapped to pins GPIO16 and GPIO17. By default, linux-gpib bitbang driver uses GPIO16 for GPIB DIO3 signal. In order to free up GPIO16, the DIO3 signal can be rewired to GPIO21 by opening positions 1-2 (cut traces between pads) and closing positions 2-3 on the solder jumper JP3.

By default, CTS and RTS signals are disconnected from the RS232 level converter chip. To connect the CTS and RTS lines, solder jumpers JP1, JP2, LP4 and JP5 need to be closed.

Note also, that the extra GPIO17 line on the I2C break out connector J4 can't be used for other purposes when system is configured for RS232 hardware flow control.

Software setup:

1. Because GPIB signal DIO3 was rewired in hardware to GPIO21, this change needs to reflected in the linux-gpib bitbang driver source code. The source file in question is: [linux-gpib-sorce-dir]/linux-gpib-kernel/drivers/gpib/gpio/gpib_bitbang.c, where the signal pairing section needs to be modified as shown below. With the modification done, the linux-gpib driver needs to be compiled as described in step 3 of the "Linux-gpib setup instructions" section of this document.

/**********************************************
 *  Signal pairing and pin wiring between the *
 *  Raspberry-Pi connector and the GPIB bus   *
 *                                            *
 *               signal           pin wiring  *
 *            GPIB  Pi-gpio     GPIB  ->  RPi *
**********************************************/
typedef enum {
        D01_pin_nr =  20,     /*   1  ->  38  */
        D02_pin_nr =  26,     /*   2  ->  37  */
//      D03_pin_nr =  16,     /*   3  ->  36  ORIGINAL AND COMMENTED OUT */
        D03_pin_nr =  21,     /*   3  ->  40  MODIFIED TO AVOID CONFLICT WITH CTS SIGNAL */
        D04_pin_nr =  19,     /*   4  ->  35  */
        D05_pin_nr =  13,     /*  13  ->  33  */
        D06_pin_nr =  12,     /*  14  ->  32  */
        D07_pin_nr =   6,     /*  15  ->  31  */
        D08_pin_nr =   5,     /*  16  ->  29  */
        EOI_pin_nr =   9,     /*   5  ->  21  */
        DAV_pin_nr =  10,     /*   6  ->  19  */
        NRFD_pin_nr = 24,     /*   7  ->  18  */
        NDAC_pin_nr = 23,     /*   8  ->  16  */
        IFC_pin_nr =  22,     /*   9  ->  15  */
        SRQ_pin_nr =  11,     /*  10  ->  23  */
        _ATN_pin_nr = 25,     /*  11  ->  22  */
        REN_pin_nr =  27,     /*  17  ->  13  */
...

2. Next the uart-ctsrts.dtbo file (included in extra directory) needs to be copied in to the /boot/overlays directory and add the following lines need to be added to the /boot/config.txt file:

enable_uart=1
dtoverlay=disable-bt
dtoverlay=uart-ctsrts

3. Reboot the system to apply changes.