Connectivity details and troubleshooting

This file provides more detailed information about setting up basic device connectivity, including possible troubleshooting steps in case something goes wrong.

Additional information may be found in the separate documents pertaining to the PTAL device name format, ptal-init, and ptal-mlcd.

General issues

Question: What connectivity diagnostic tools are available?

Question: My device has both a parallel and a USB port. Which one should I use?

If you are connecting the device directly to your computer, you should connect via USB if possible, because that will yield better performance.

Question: My device only has a parallel port, but my computer doesn't have an available parallel port. Can I use a USB-to-parallel converter?

No. You might be able to print only, but not through the hpoj software.

Problem: I get a "command not found" error message when I run "ptal-init setup" or any of the device connectivity tests.

Refer to the Post-installation steps for setting the PATH environment variable. (You may just need to log out and back in again.) You can also manually specify the path on the command line, for example, "/usr/local/sbin/ptal-init setup".

Problem: I used "ptal-init setup" to add a device and specified a different device name suffix than the one proposed. I later specified this suffix when asked for a device name but was told that it was not a valid device name.

In the steps for setting up parallel- and USB-connected devices, "ptal-init setup" proposes a default device name to use and invites you to specify a different device name suffix if you'd like. In this case you don't need to specify the full device name (with the mlc:par: or mlc:usb: prefix). However, in all other cases you must specify the full device name, including the prefix.

Question: Is it necessary to run "ptal-init start" after "ptal-init setup"?

No. "ptal-init setup" automatically stops and re-starts the daemons as necessary.

Problem: I ran "ptal-init setup" and the device connectivity tests passed. Then I rebooted, and now the same tests fail.

Perhaps the necessary kernel modules are no longer loaded, or a conflicting kernel module (such as scanner.o) is now loaded that wasn't loaded before. For Linux, run /sbin/lsmod to be sure. For Linux, "ptal-init setup" and "ptal-init start" attempt to load some of the necessary kernel modules before probing or starting daemons for a parallel-port or USB device (hpoj-0.90 didn't do this at "ptal-init start" time). However, this could break if the relevant kernel modules aren't named as expected (lp.o and printer.o).

Problem: I get one or more error messages on the console (or text-mode login screen) if I boot with the device disconnected or powered off.

When CUPS starts, it tries to probe the system for available devices. When it gets to the ptal backend, ptal-cups tries to probe all devices that have been registered with "ptal-init setup". You will see at least one (for USB) or more (for parallel) error messages for each PTAL device that isn't connected and powered on. This is normal and nothing to be concerned about.

Problem: My device has both a USB and a parallel port. I connected different computers to each port, but only one of the computers is able to communicate with it.

Most HP peripherals with both parallel and USB ports don't support connecting both at the same time. If you want to share the device, you can either network it with an hpoj-supported HP JetDirect print server, or share it out to the network from a single computer.

The HP OfficeJet D and 7100 series are notable exceptions, in that they can handle connections over both the USB port and LIO interface, which accepts either a parallel-port or a JetDirect cartridge.

Problem: I switched my device from parallel to USB (or vice-versa), but now "ptal-init setup" can't communicate with it.

Make sure you power-cycle the device after changing the connection type, to get it into the right state to detect connections on the new port.

Also see the troubleshooting information for the specific connection type (parallel, USB, or JetDirect) elsewhere in this document.

Problem: The basic device connectivity tests segfault or give unresolved-symbol error messages.

You probably have (at least one piece of) an older hpoj version still installed on your system. Refer to the Compiling and installing the software document for information on completely removing old hpoj versions from your system.

Problem: After hand-editing a PTAL device configuration file, I have duplicate devices.

Some text editors create backup files by appending an extension such as ".bak" or a tilde ("~"), and some people manually do this by appending an extension such as ".old" or ".original". Since ptal-init and libptal match device configuration files based on the beginning of the name, this may result in duplicate devices such as "mlc:usb:OfficeJet_G85~". To fix this, simply delete (or move to a different directory) the offending files, and run "ptal-init start" to verify that the duplicate devices are eliminated.

Parallel-port issues

Question: On which platforms are parallel connections supported?

Linux/i386, Linux/Alpha, and FreeBSD/i386 are known to work. Other CPU architectures under Linux and FreeBSD may work if they provide a similar access method to parallel-port hardware registers from user mode. Other operating systems, such as NetBSD, OpenBSD, HP-UX, etc., will not work, because they don't allow user-mode access to the parallel-port hardware registers, and their kernel-mode drivers probably don't provide the degree of control over parallel-port signalling that ptal-mlcd requires.

Question: What version of Linux or FreeBSD do I need for parallel-port support?

Since ptal-mlcd drives the parallel port from user mode, any version of these kernels should work.

It doesn't matter if parallel-port support is compiled into the kernel or not, or if it's dynamically or statically linked. If there is kernel parallel-port support, then you should tell "ptal-init setup" which kernel device file corresponds to the parallel port in use, so that ptal-mlcd can open it and prevent other processes from interfering with its use of the parallel port.

On Linux 2.2 and 2.4 systems with kernel parallel-port support compiled and linked in (either statically or loaded as modules), "ptal-init setup" is usually able to consult files under /proc to detect your parallel-port base addresses. Otherwise, you may need to determine and supply this information yourself. 0x378 is probably the most common base address for motherboard-integrated parallel ports; 0x278 and 0x3BC are other possibilities for integrated or ISA parallel ports. PCI add-in parallel ports typically have very different base addresses. Be very careful about entering this information, because probing incorrect I/O port addresses could result in system instability and/or data loss.

Problem: After a parallel-connected device is power cycled or disconnected/reconnected, an hpoj command reports a communication error.

ptal-mlcd currently doesn't always detect when a parallel-connected device is disconnected or power cycled when it's idle. Therefore, when the device is connected and powered on again, you may experience a failure when you run an application that tries to access the device. In most cases, if you retry the operation it will succeed the second time.

Question: To what mode should my parallel-port be set?

In order from most- to least-preferred: ptal-mlcd issues an informational syslog message at startup to tell you what kind of parallel-port setting (in the form of its -porttype command-line switch) it detected.

ptal-mlcd issues a warning error message at startup if it detects a unidirectional-only parallel port. If it's not possible to set your parallel port to a better mode, then you can add the "-porttype spp" switch to the ptal-mlcd command line to get rid of this error message, but as explained above, you may still experience communication problems with certain models.

Problem: I experience parallel-port communication problems when running certain other software.

Be careful not to load kernel modules that conflict with ptal-mlcd's use of the parallel port. Typical examples of conflicting kernel modules include the following: Other user-mode applications which like ptal-mlcd bypass the kernel to access the parallel-port registers directly without performing similar kernel device locking can also interfere with ptal-mlcd's signalling.

Problem: I have trouble configuring or communicating with my LaserJet 1100 or 1100A.

Some people have reported difficulties specific to these models, especially after leaving them powered on for a while. Try power-cycling the device to get it back in a good state. It is recommended that you not leave these particular models powered on all the time when you're not using them.

Problem: ptal-connect to the ECHO service fails or doesn't work very well.

The ECHO service on the OfficeJet LX and 300 series doesn't work reliably. Don't use it on those models.

USB issues

Question: On which platforms are USB connections supported?

Mainly Linux, as long as you have an appropriate kernel version (see below).

In theory, other operating systems such as *BSD may also work in conjunction with libusb (see below).

Question: What version of the Linux kernel do I need for USB support?

That depends on what model you have.

At a minimum you need 2.2.19 or later, or 2.4.2 or later. Earlier kernel versions had several bugs in the USB printer-class driver (printer.c) related to bidirectional communcation, which ptal-mlcd definitely requires.

For many models, 2.2.19+ or 2.4.2+ is sufficient. (Specifically, if according to usbview the device's first interface alternate setting has a class/subclass/protocol ID of 7/1/3.)

However, for some models, such as the PhotoSmart printers 1000/1100/12xx and most newer OfficeJet- and PSC-branded products, you need a minimum of 2.4.19 (actually 2.4.19-pre5 or the 2.4.18 kernel shipped with RedHat 7.3) or 2.5.7. (Specifically, if according to usbview the device does not have an interface alternate setting with a class/subclass/protocol ID of 7/1/3. Some enhancements were added into these kernel versions to provide ptal-mlcd more control over the USB printer-class device setup and interface alternate setting selection.)

In addition, some models, such as those that support the LIDIL print language instead of PCL, also require libusb, or you won't be able to connect to the print service through hpoj.

Refer to the hpoj Supported devices page for more information.

Question: What is the difference between printer.c and printer.o?

Technically, printer.c is the source code file and printer.o is the binary/compiled/object-code file. However, to some extent they are used interchangeably in the hpoj documentation.

Question: What should I do if my kernel has USB support but (according to the previous question) printer.c won't work for my model?

If your kernel doesn't have USB support at all (for example, 2.2.17 or earlier), then you must upgrade the kernel, but see the next question for additional USB setup needed. Or you can upgrade your whole system to a newer distribution that includes the necessary kernel support and setup.

If your kernel otherwise has USB support, then the best option may be to get the USB printer.c update from the hpoj Download page. That version of printer.c should work on any USB-capable 2.2 or 2.4 kernel version and contains the same hpoj-related enhancements from 2.4.19. Follow the installation instructions in its README file.

Important: If you already have the correct kernel version, then you should not replace printer.c with the modified version mentioned in the previous paragraph.

Question: How do I add USB support to an older Linux distribution (or when recompiling my kernel)?

First of all, you'll need to upgrade to the latest 2.2 or 2.4 kernel, and you may also need to update the printer.c file.

The following kernel configuration options must be enabled:

The following kernel modules must be loaded (via /sbin/modprobe or /sbin/insmod): As an alternative to loading all needed drivers at startup, you can set up a "hot-plug" script to do this dynamically. This procedure will not be explained here, but you can get more information on the Linux USB home page. However, it is not recommended to use this mechanism to load the hpoj daemons, such as ptal-mlcd.

Be sure to mount /proc/bus/usb (of file-system type usbdevfs), either manually or at startup from /etc/fstab. /proc/bus/usb/devices provides useful (although somewhat cryptic) information about the devices attached to the bus. The usbview utility displays the same information in a more readable fashion.

If necessary, create the directory /dev/usb. In that directory, issue the following commands to create nodes for USB printer-class devices: 

	mknod lp0 c 180 0
	mknod lp1 c 180 1
	#       ^       ^    <-- Increment both of these numbers.
etc., as many as you need, but don't go past 15. Set the permission and ownership as desired (for example, 0660 and root:daemon).

Question: How do I get USB working on a non-Linux platform such as FreeBSD?

First, make sure you install libusb and the hpoj ./configure script detects it.

Next, make sure that there are no other drivers (such as for USB printer-class devices) bound to the device. You may need to reconfigure/recompile your kernel, unload module(s) (on FreeBSD, possibly with a command such as "/sbin/kldunload ulpt"), or kill process(es).

At the time of this writing, there have been a number of failure reports about this on FreeBSD and Mac OS X, and only one success report on FreeBSD (in that case, FreeBSD-4.7, but your mileage may vary). If you need help with this, ask on the hpoj-devel mailing list, but if all else fails you may end up needing to try this on a later version of your operating system or on a different operating system such as Linux.

Problem: I have an SMP (Symmetric Multi-Processor) system, and I experience kernel OOPSes or complete system lockups when using USB.

Linux kernel 2.2 and 2.4 versions have SMP-related bugs in the USB subsystem, at least in the printer-class driver (printer.o) when back-channel data is transferred, which happens with hpoj but not with raw printing. (One user suggested that these issues may have been resolved in the 2.5/2.6 kernel series, but this has not been verified.)

Verify that hpoj was built with libusb support. "ptal-init setup" should detect this situation and enable a workaround (disable printer.o and only use libusb), but this wouldn't have happened if you originally ran it in non-SMP mode and are now running in SMP mode.

To see if SMP is really the problem for you, try rebooting your system into UP (Uni-Processor) mode (pass the nosmp option to the kernel).

Problem: My system locks up when I disconnect or power off the device.

This is a problem in earlier kernel versions, when ptal-mlcd has an open connection to the device. Running "ptal-init stop" to kill ptal-mlcd before disconnecting or powering off the device may prevent this problem from happening. Apparently some fixes were made in 2.4.7 and later to address this issue. You might be able to just upgrade printer.c (see above).

Problem: "ptal-init setup" can't find my device, it finds it but says it can't communicate with it, or I experience I/O errors at a later time such as while printing, scanning, or accessing photo-cards.

Problem: I also have a non-hpoj USB printer. Sometimes ptal-mlcd complains about not being able to find its device, or I have trouble printing to the non-hpoj USB printer.

Depending on what order USB printers are plugged in and/or powered on, they could be assigned to different /dev/usb/lpX device nodes at different times. ptal-mlcd handles this situation, but if your print queue for the non-hpoj USB printer references a particular device node, then you must update it accordingly as its device node changes, to ensure that it doesn't inadvertently open ptal-mlcd's device node instead.

Run "ptal-init setup" to check whether somebody allowed it to take over the non-hpoj printer. In general, hpoj was designed for use with most HP multi-function peripherals, and may not work with single-function printers. In particular, there are issues with hpoj in conjunction with various HP DeskJet models (especially 800 and 900 series).

As described above, if you have an SMP Linux system, "ptal-init setup" may have blacklisted the printer.o kernel module. This has the side effect of disabling /dev/usb/lp*-style access to all USB printers. If this is a problem, then you may need to switch back and forth between the two (sets of) devices using the following steps:

To access hpoj device(s):

  1. Blacklist printer.o (see below).
  2. Run "/sbin/rmmod printer".
  3. Run "ptal-init start".
To access non-hpoj USB printer(s):
  1. Run "ptal-init stop".
  2. Un-blacklist printer.o (see below).
  3. Run "/sbin/modprobe printer".

Problem: I have a non-hpoj single-function USB scanner, and it quit working after setting up an hpoj device.

As described above, the Linux kernel USB scanner.o driver conflicts with hpoj's use of certain device models, and therefore "ptal-init setup" must blacklist and unload scanner.o. This may break access to USB single-function scanners, requiring you to reconfigure them to use libusb instead of scanner.o. If that's not possible, then you may need to modify the product ID table in scanner.h and recompile/reinstall scanner.o to prevent it from binding to your hpoj device (which it never should have done in the first place). Also, see below about un-doing the blacklisting of scanner.o.

Question: How do I manually blacklist (prevent from automatically loading) or un-blacklist a Linux kernel module such as printer.o or scanner.o?

Assuming you want to blacklist printer.o:
  1. Add to /etc/modules.conf the line "alias printer off".
  2. Add to /etc/hotplug/blacklist the line "printer".
  3. Run "/sbin/rmmod printer".
To un-do the blacklisting:
  1. Remove or comment out (prepend with "#") the lines that were added to the above-mentioned two files.
  2. Run "/sbin/modprobe printer" if desired.

Problem: ptal-connect or ptal-printd can't connect to the print service on the device. Print jobs get stuck in the queue.

Chances are that hpoj (or more specifically, ptal-mlcd) was not built for libusb support. Refer to the "Compiling and installing the software document for more information. In particular, depending on your distribution you may also need to have both libusb and libusb-devel packages installed.

"ptal-init setup" checks for libusb support and warns you if it's missing. You can check for this yourself by referring back to the ./configure script output (if it's still available) or by running a command such as "ldd /usr/local/sbin/ptal-mlcd | grep libusb".

Problem: Printing is extremely slow.

This is a known issue in a certain combination of circumstances: The best way to fix this is probably to load printer.o (or whatever it happens to be called on your system). Of course, this goes against the usual advice of avoiding printer.o on SMP systems, but under the circumstances it may be worth a try, in case the relevant SMP problems don't hit in this mode of operation. Just be prepared to back it out if necessary.

Another possible fix is to disable "composite USB" mode. This will not work on the PhotoSmart 145/245-series products or on any product that uses LIDIL instead of PCL (run "ptal-devid -cmd" and look for the token LDL). To make this change, edit the device configuration file (such as /etc/ptal/mlc:usb:psc_2500_series), add the line "init.mlcd.append+=-nocomp", and run "ptal-init start" to make it take effect. After making this change, it would be a good idea to re-run the basic device connectivity tests, especially the part about testing print-service connectivity, to make sure this change didn't break anything. (For the PhotoSmart 145 and 245, you can actually get by without using hpoj at all, and instead use raw printing directly to the device and a standard USB mass-storage-interface kernel driver.)

Problem: I get an I/O error or interrupted print job when inserting or removing a photo card on the DeskJet 450.

This is an issue with the device, where it registers a USB disconnect and reconnect (I'm not sure what it does over parallel) when a photo card is inserted or removed. For this model, take care to insert or remove photo cards only when the device is idle.

JetDirect issues

Problem: ptal-devid can't retrieve the device ID string.

There are several possible causes:

Problem: ptal-connect to the ECHO service fails.

There are several possible causes:

Problem: I can't do anything besides printing to the device, or I can do everything except printing to the device.

Check the JetDirect configuration page and verify that the communication mode is MLC or 1284.4. Note that some device models don't have full-feature JetDirect support. See the hpoj Supported devices page for more information on which device models are networkable with which JetDirect models.

Miscellaneous issues

Problem: The device clock drifts over time and/or is wrong after a power cycle.

This is a device-side issue.

Problem: I couldn't set the clock on my device.

Non-fax-capable models generally don't have a working clock. If there's no way to set it from the front panel, then chances are it can't be set from software either.

Problem: After setting the device's clock with "ptal-hp clock -set, the clock gets "stuck" and no longer advances.

This has been observed on some (but not necessarily all) PSC 2210 units. The root cause is currently unknown. Try setting the clock from the device's front-panel menu.

Problem: After being left on for a period of time, the device stops answering incoming phone calls and/or receiving faxes.

This is a known firmware bug on the LaserJet 3200 series that may be resolved with a firmware upgrade, possibly in the form of an add-in DIMM available by contacting the appropriate "official" HP customer-support service (not the hpoj project).

Next steps

Use the Back button on your browser to return to the previous document, or click here to return to the index.