Device Drivers, Part 12: USB Drivers in Linux Continued

USB Devices in Linux

The 12th part of the series on Linux device drivers takes you further along the path to writing your first USB driver in Linux — a continuation from the previous article.

Pugs continued, “Let’s build upon the USB device driver coded in our previous session, using the same
handy JetFlash pen drive from Transcend, with the vendor ID 0x058f and product ID 0×6387. For that, let’s dig further into the USB protocol, and then convert our learning into code.”

USB endpoints and their types

Depending on the type and attributes of information to be transferred, a USB device may have one or more endpoints, each belonging to one of the following four categories:

  • Control — to transfer control information. Examples include resetting the device, querying information about the device, etc. All USB devices always have the default control endpoint point as zero.
  • Interrupt — for small and fast data transfers, typically of up to 8 bytes. Examples include data transfer for serial ports, human interface devices (HIDs) like keyboards, mouse, etc.
  • Bulk — for big but comparatively slower data transfers. A typical example is data transfers for mass-storage devices.
  • Isochronous — for big data transfers with a bandwidth guarantee, though data integrity may not be guaranteed. Typical practical usage examples include transfers of time-sensitive data like audio, video, etc.

Additionally, all but control endpoints could be “in” or “out”, indicating the direction of data transfer; “in” indicates data flow from the USB device to the host machine, and “out”, the other way.

Technically, an endpoint is identified using an 8-bit number, the most significant bit (MSB) of which indicates the direction — 0 means “out”, and 1 means “in”. Control endpoints are bi-directional, and the MSB is ignored.

Figure 1 shows a typical snippet of USB device specifications for devices connected on a system.

USB's proc window snippet

Figure 1: USB's proc window snippet (click for larger view)

To be specific, the E: lines in the figure show examples of an interrupt endpoint of a UHCI Host Controller, and two bulk endpoints of the pen drive under consideration. Also, the endpoint numbers (in hex) are, respectively, 0x81, 0x01 and 0x82 — the MSB of the first and third being 1, indicating ‘in’ endpoints, represented by (I) in the figure; the second is an (O) or ‘out’ endpoint. MxPS specifies the maximum packet size, i.e., the data size that can be transferred in a single go. Again, as expected, for the interrupt endpoint, it is 2 (<=8), and 64 for the bulk endpoints. Ivl specifies the interval in milliseconds to be given between two consecutive data packet transfers for proper transfer, and is more significant for the interrupt endpoints.

Decoding a USB device section

As we have just discussed regarding the E: line, it is the right time to decode the relevant fields of others as well. In short, these lines in a USB device section give a complete overview of the device as per the USB specifications, as discussed in our previous article.

Refer back to Figure 1. The first letter of the first line of every device section is a T, indicating the position of the device in the USB tree, uniquely identified by the triplet <usb bus number, usb tree level, usb port>. D represents the device descriptor, containing at least the device version, device class/category, and the number of configurations available for this device.

There would be as many C lines as the number of configurations, though typically, it is one. C, the configuration descriptor, contains its index, the device attributes in this configuration, the maximum power (actually, current) the device would draw in this configuration, and the number of interfaces under this configuration.

Depending on this, there would be at least that many I lines. There could be more in case of an interface having alternates, i.e., the same interface number but with different properties — a typical scenario for Web-cams.

I represents the interface descriptor with its index, alternate number, the functionality class/category of this interface, the driver associated with this interface, and the number of endpoints under this interface.

The interface class may or may not be the same as that of the device class. And
depending on the number of endpoints, there would be as many E lines, details of which have already been discussed earlier.

The * after the C and I represents the currently active configuration and interface, respectively. The P line provides the vendor ID, product ID, and the product revision. S lines are string descriptors showing up some vendor-specific descriptive information about the device.

“Peeping into cat /proc/bus/usb/devices is good in order to figure out whether a device has been detected or not, and possibly to get the first-cut overview of the device. But most probably this information would be required to write the driver for the device as well. So, is there a way to access it using C code?” Shweta asked.

“Yes, definitely; that’s what I am going to tell you about, next. Do you remember that as soon as a USB device is plugged into the system, the USB host controller driver populates its information into the generic USB core layer? To be precise, it puts that into a set of structures embedded into one another, exactly as per the USB specifications,” Pugs replied.

The following are the exact data structures defined in <linux/usb.h>, ordered here in reverse, for flow clarity:

struct usb_device
{
	…
	struct usb_device_descriptor descriptor;
	struct usb_host_config *config, *actconfig;
	…
};
struct usb_host_config
{
	struct usb_config_descriptor desc;
	…
	struct usb_interface *interface[USB_MAXINTERFACES];
	…
};
struct usb_interface
{
	struct usb_host_interface *altsetting /* array */, *cur_altsetting;
	…
};
struct usb_host_interface
{
	struct usb_interface_descriptor desc;
	struct usb_host_endpoint *endpoint /* array */;
	…
};
struct usb_host_endpoint
{
	struct usb_endpoint_descriptor desc;
	…
};

So, with access to the struct usb_device handle for a specific device, all the USB-specific information about the device can be decoded, as shown through the /proc window. But how does one get the device handle?

In fact, the device handle is not available directly in a driver; rather, the per-interface handles (pointers to struct usb_interface) are available, as USB drivers are written for device interfaces rather than the device as a whole.

Recall that the probe and disconnect callbacks, which are invoked by the USB core for every interface of the registered device, have the corresponding interface handle as their first parameter. Refer to the prototypes below:

int (*probe)(struct usb_interface *interface, const struct usb_device_id *id);
void (*disconnect)(struct usb_interface *interface);

So, with the interface pointer, all information about the corresponding interface can be accessed — and to get the container device handle, the following macro comes to the rescue:

struct usb_device device = interface_to_usbdev(interface);

Adding this new learning into last month’s registration-only driver gets the following code listing (pen_info.c):

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/usb.h>

static struct usb_device *device;

static int pen_probe(struct usb_interface *interface, const struct usb_device_id *id)
{
    struct usb_host_interface *iface_desc;
    struct usb_endpoint_descriptor *endpoint;
    int i;

    iface_desc = interface->cur_altsetting;
    printk(KERN_INFO "Pen i/f %d now probed: (%04X:%04X)\n",
            iface_desc->desc.bInterfaceNumber, id->idVendor, id->idProduct);
    printk(KERN_INFO "ID->bNumEndpoints: %02X\n",
            iface_desc->desc.bNumEndpoints);
    printk(KERN_INFO "ID->bInterfaceClass: %02X\n",
            iface_desc->desc.bInterfaceClass);

    for (i = 0; i < iface_desc->desc.bNumEndpoints; i++)
    {
        endpoint = &iface_desc->endpoint[i].desc;

        printk(KERN_INFO "ED[%d]->bEndpointAddress: 0x%02X\n",
                i, endpoint->bEndpointAddress);
        printk(KERN_INFO "ED[%d]->bmAttributes: 0x%02X\n",
                i, endpoint->bmAttributes);
        printk(KERN_INFO "ED[%d]->wMaxPacketSize: 0x%04X (%d)\n",
                i, endpoint->wMaxPacketSize, endpoint->wMaxPacketSize);
    }

    device = interface_to_usbdev(interface);
    return 0;
}

static void pen_disconnect(struct usb_interface *interface)
{
    printk(KERN_INFO "Pen i/f %d now disconnected\n",
            interface->cur_altsetting->desc.bInterfaceNumber);
}

static struct usb_device_id pen_table[] =
{
    { USB_DEVICE(0x058F, 0x6387) },
    {} /* Terminating entry */
};
MODULE_DEVICE_TABLE (usb, pen_table);

static struct usb_driver pen_driver =
{
    .name = "pen_driver",
    .probe = pen_probe,
    .disconnect = pen_disconnect,
    .id_table = pen_table,
};

static int __init pen_init(void)
{
    return usb_register(&pen_driver);
}

static void __exit pen_exit(void)
{
    usb_deregister(&pen_driver);
}

module_init(pen_init);
module_exit(pen_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Anil Kumar Pugalia <[email protected]>");
MODULE_DESCRIPTION("USB Pen Info Driver");

Then, the usual steps for any Linux device driver may be repeated, along with the pen drive steps:

  • Build the driver (pen_info.ko file) by running make.
  • Load the driver using insmod pen_info.ko.
  • Plug in the pen drive (after making sure that the usb-storage driver is not already loaded).
  • Unplug the pen drive.
  • Check the output of dmesg for the logs.
  • Unload the driver using rmmod pen_info.

Figure 2 shows a snippet of the above steps on Pugs’ system. Remember to ensure (in the output of cat /proc/bus/usb/devices) that the usual usb-storage driver is not the one associated with the pen drive interface, but rather the pen_info driver.

Output of dmesg

Figure 2: Output of dmesg

Summing up

Before taking another break, Pugs shared two of the many mechanisms for a driver to specify its device to the USB core, using the struct usb_device_id table. The first one is by specifying the <vendor id, product id> pair using the USB_DEVICE() macro (as done above). The second one is by specifying the device class/category using the USB_DEVICE_INFO() macro. In fact, many more macros are available in <linux/usb.h> for various combinations. Moreover, multiple of these macros could be specified in the usb_device_id table (terminated by a null entry), for matching with any one of the criteria, enabling to write a single driver for possibly many devices.

“Earlier, you mentioned writing multiple drivers for a single device, as well. Basically, how do we selectively register or not register a particular interface of a USB device?”, queried Shweta. “Sure. That’s next in line of our discussion, along with the ultimate task in any device driver — the data-transfer mechanisms,” replied Pugs.

  • Pingback: Need small code/small demo project for USB Pendrive device driver code.(USB Flash )

  • MenDuong

    Dear, When I pug and unplug my USB driver. I can’t see message in dmesg as above.

    My dmesg as follow:

    SELinux: initialized (dev sdd1, type vfat), uses genfs_contexts

    usb 2-1: USB disconnect, address 5

    SELinux: initialized (dev sdb4, type fuseblk), uses genfs_contexts

    lo: Disabled Privacy Extensions

    SELinux: initialized (dev proc, type proc), uses genfs_contexts

    lo: Disabled Privacy Extensions

    SELinux: initialized (dev proc, type proc), uses genfs_contexts

    lo: Disabled Privacy Extensions

    SELinux: initialized (dev proc, type proc), uses genfs_contexts

    lo: Disabled Privacy Extensions

    SELinux: initialized (dev proc, type proc), uses genfs_contexts

    usbcore: deregistering interface driver pen_driver

    usbcore: registered new interface driver pen_driver

    usb 2-1: new high speed USB device using ehci_hcd and address 6

    usb 2-1: New USB device found, idVendor=1221, idProduct=3234

    usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3

    usb 2-1: Product: Udisk 2.0

    usb 2-1: Manufacturer: Udisk

    usb 2-1: SerialNumber: 00000000295B

    usb 2-1: configuration #1 chosen from 1 choice

    scsi8 : SCSI emulation for USB Mass Storage devices

    usb-storage: device found at 6

    usb-storage: waiting for device to settle before scanning

    usb-storage: device scan complete

    scsi 8:0:0:0: Direct-Access Udisk Udisk 2.0 3.00 PQ: 0 ANSI: 2

    sd 8:0:0:0: Attached scsi generic sg5 type 0

    sd 8:0:0:0: [sdd] 16384000 512-byte logical blocks: (8.38 GB/7.81 GiB)

    sd 8:0:0:0: [sdd] Write Protect is off

    sd 8:0:0:0: [sdd] Mode Sense: 0b 00 00 08

    sd 8:0:0:0: [sdd] Assuming drive cache: write through

    sd 8:0:0:0: [sdd] Assuming drive cache: write through

    sdd: sdd1

    sdd: p1 size 16386237 exceeds device capacity, limited to end of disk

    sd 8:0:0:0: [sdd] Assuming drive cache: write through

    sd 8:0:0:0: [sdd] Attached SCSI removable disk

    SELinux: initialized (dev sdd1, type vfat), uses genfs_contexts

    usb 2-1: USB disconnect, address 6

    • http://twitter.com/anil_pugalia Anil Pugalia

      Because the usb-storage driver is loaded. You need to make sure that is unloaded, as mentioned in the article.

      • MenDuong

        Thank you. Please, how to unload usb-storage?

        • http://twitter.com/anil_pugalia Anil Pugalia

          If it is listed in lsmod, just do a “rmmod usb-storage”. Otherwise, you’d have to recompile your kernel, by making usb-storage as a module.

        • micheal

          go drivers path and then type rmmod usb-storage

  • MELWIN JOSE

    I got an error when i tried to remove the “usb_storage”

    melwin-Satellite-L640 USB_2 # rmmod usb_storage
    ERROR: Module usb_storage is in use by ums_realtek

    Here is the output for “lsusb”
    Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
    Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
    Bus 001 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
    Bus 002 Device 002: ID 8087:0020 Intel Corp. Integrated Rate Matching Hub
    Bus 002 Device 005: ID 0930:0214 Toshiba Corp.
    Bus 002 Device 006: ID 04f2:b1d6 Chicony Electronics Co., Ltd

    • MELWIN JOSE

      solved :)
      ums_realtk is a module that depends in usb_storage.
      just “rmmod ums_realtk”

      • Mayank

        I’m getting the same error but on trying the same command, I got
        “Error: Module ums_realtek does not exist in /proc/modules”. I also listed all the available modules & ums-realtek isn’t present there. However, it’s there in the folder. I’m a newbie. Please help.

        • anil_pugalia

          Paste the output of lsmod.

  • David

    Its Fantastic !!
    Thank you for your valuable Linux device driver articles.

    Could you please start the same for BSP also.

    • anil_pugalia

      I doubt, if it would be possible, as currently doing the same for mathematics in open source.

  • aadhirai

    I have tried the code in Part 11 which was working for me.

    Here I am not getting the /dev/pen0 listed on my system (Linux Ubuntu 12.04), even when I copy paste the code from here….

    compiled & followed all your steps accordingly..
    Will you please help me in completing this ?

    • anil_pugalia

      Check out the vendor id, device id of your pen drive, and update the code accordingly.

  • anil kumar

    how to know the functions

    pen_probe,pen_disconnect (where these functions available and how to find the headder files)

    • anil_pugalia

      Those are our implementations, coded in the above article example itself

  • jakub

    I have written code that read data about battery and light conditions from keyboard but i must detach& read & attach my keyboard and read get some time … in this time i cant write using mi keyboard(is detached) … is here some way how to do R/W without detaching device ???

    • anil_pugalia

      Please elaborate, as not very clear on the reason for your detach & attach.

  • Garvit Sharma

    Can not we write a driver which works for all usb pendrives without actually taking vendor-id and product-id ?

    • anil_pugalia

      In fact, that’s how the actual driver “usb-storage” is written. It works on the concept of class, i.e. the category of devices, rather than their vendor & device id. Thus, usb-storage serves all the storage class devices, including all the pen drives.

      • Garvit Sharma

        Then, how to hack “usb-storage” ?

        • anil_pugalia

          Why do you need to hack in it? Its complete code is there part of the kernel source code.

          • Garvit Sharma

            I mean, how to understand that code and modify it for our own purpose ?

          • anil_pugalia

            It involves understanding the USB Storage protocol, which is SCSI based.

          • Garvit Sharma

            Ok, It would be great if you could help me with that.

          • anil_pugalia

            How do you expect me to help? You have to first read those stuff, and the easiest would be to start reading the usb-storage code itself.

          • Garvit Sharma

            Ok, thank you sir!!

  • pmalleus

    Dear Anil_Pugalia,

    Thank you for your really pedagogical articles. The module pen_register from Part11 worked perfectly well after addition of #include .
    Unfortunatly the module pen_info from Part12 does’nt act as expected : the module usb_storage always preempt pen_info : after removing usb_storage via rmmod and adding pen_info.ko, I plug the pen drive, and usb_storage comes back after pen_info as shows lsmod. A sudo more /sys/kernel/debug/usb/devices shows that the driver of my pen drive is usb-storage. If I try to rmmod usb_storage, the answer is Error: Module usb_storage is in use.
    In other words I don’t see how to avoid the automatic substitution of pen_info by usb_storage.
    Thank you for any advice.

    Best Regards

    • anil_pugalia

      Try commenting the usb-storage lines in /lib/modules//modules.usbmap

      But do not forget to uncomment, once you are done experimenting.

  • tammanagari tirupathi reddy

    Dear anil kumar,

    I am trying to write device driver for avr programmer, manufactured by ‘zhifengsoft’, for which i donot have linux driver. As part of this, first I wrote upto registering the usb devie and deregestering the usb device in init and exit functions respectavely. and an empty probe function with printk saying that my programmer is connected message.
    But I am not getting the message which i gave in probe function.
    Driver is compiled perfectly and regestered. The vender id and product id I collected using lsusb -v and i also verified it by connecting and checking the dmesg.

    Can you please help in this context.

    Thanking you sir.
    This is my code snippet:
    static struct usb_device_id avrProg_table [] = {
    { USB_DEVICE(AVR_PROG_VENDOR_ID, AVR_PROG_PRODUCT_ID) },
    { }
    };

    MODULE_DEVICE_TABLE(usb, avrProg_table);
    static int avrProg_probe(struct usb_interface *interface, const struct usb_device_id *id)
    {
    /* called when a USB device is connected to the computer. */
    printk(“nnnavr_programmer is connected!!!nnn”);
    return 0;
    }
    static void avrProg_disconnect(struct usb_interface *interface)
    {
    /* called when unplugging a USB device. */
    printk(“nnnavr_programmer is disconnected!!nnn”);
    }
    static struct usb_driver avrProg_driver = {
    .name = “avr_programmer”,
    .id_table = avrProg_table,
    .probe = avrProg_probe,
    .disconnect = avrProg_disconnect,
    };
    #endif
    static int __init avrProg_init(void) {
    printk(” avrProg installed!n”);
    return usb_register(&avrProg_driver);;
    }
    static void __exit avrProg_exit(void) {
    printk(” avrProg uninstalledn”);
    usb_deregister(&avrProg_driver);;
    }
    module_init(avrProg_init);
    module_exit(avrProg_exit);

  • tammanagari tirupathi reddy

    Dear anil kumar,

    I am trying to write device driver for avr programmer, manufactured by ‘zhifengsoft’, for which i donot have linux driver. As part of this, first I wrote upto registering the usb devie and deregestering the usb device in init and exit functions respectavely. and an empty probe function with printk saying that my programmer is connected message.
    But I am not getting the message which i gave in probe function.
    Driver is compiled perfectly and regestered. The vender id and product id I collected using lsusb -v and i also verified it by connecting and checking the dmesg.

    Can you please help in this context.

    Thanking you sir.
    This is my code snippet:
    static struct usb_device_id avrProg_table [] = {
    { USB_DEVICE(AVR_PROG_VENDOR_ID, AVR_PROG_PRODUCT_ID) },
    { }
    };

    MODULE_DEVICE_TABLE(usb, avrProg_table);
    static int avrProg_probe(struct usb_interface *interface, const struct usb_device_id *id)
    {
    /* called when a USB device is connected to the computer. */
    printk(“nnnavr_programmer is connected!!!nnn”);
    return 0;
    }
    static void avrProg_disconnect(struct usb_interface *interface)
    {
    /* called when unplugging a USB device. */
    printk(“nnnavr_programmer is disconnected!!nnn”);
    }
    static struct usb_driver avrProg_driver = {
    .name = “avr_programmer”,
    .id_table = avrProg_table,
    .probe = avrProg_probe,
    .disconnect = avrProg_disconnect,
    };
    #endif
    static int __init avrProg_init(void) {
    printk(” avrProg installed!n”);
    return usb_register(&avrProg_driver);;
    }
    static void __exit avrProg_exit(void) {
    printk(” avrProg uninstalledn”);
    usb_deregister(&avrProg_driver);;
    }
    module_init(avrProg_init);
    module_exit(avrProg_exit);

    • anil_pugalia

      Check out for any other driver owning the interface of your AVR programmer. For that you may, check the “Driver=…” entry for your device in the output of the “cat /sys/kernel/debug/usb/devices”. The debugfs should have been already mounted at /sys/kernel/debug for this.

  • Akshay Oswal

    Okay, silly question. There’s no usb folder in proc/bus.

    • Akshay

      Is that the same as /sys/kernel/usb/devices ?

      • preetham

        which linux kernel u r using Akshay oswal?

        i m also facing same problem

        • anil_pugalia

          In the latest kernels that has been deprecated. So, one should checkout the /sys/kernel/debug/usb/devices. And for that you need to make sure that the debugfs is mounted at /sys/kernel/debug

  • mirunazhini

    how to make pen_info module to run for any pen drive.

    • anil_pugalia

      Try changing the USB_DEVICE() entry to USB_INTERFACE_INFO(USB_CLASS_MASS_STORAGE, USB_SC_SCSI, USB_PR_BULK)

      • mirunazhini

        Thank you sir..

  • Basuiti

    sir,
    After inserting the module ie usb data transfer to and fro to usb device /dev/pen0 is created but i am not able to read or write to it.Can you tell me how to do it.

    • anil_pugalia

      It is not expected to do actual reads/writes. For that, you will have to study the USB Storage protocol and then send the transactions, accordingly.

  • Jaymin D

    I want to do some changes in USB driver in my kernel 3.0.35…
    So please describe me that where can I find USB driver in kernel tree/files ???
    and how can I do changes into it ??

    Request to please explain me in little bit.I am new to kernel programming particular to driver so..

    Need a help for this issue.

    Please Reply me ASAP

    Thanks..

    Regards

    Jaymin D

    • anil_pugalia

      In general, usb drivers could be found under drivers/usb under the kernel source tree.

      • Jaymin D

        Thanks a lot sir for this.but I have one Q that can I able to do some changes into it ?

        Mean that ,

        Can I add my source lines ??
        How can I compile it after adding my custom lines ??
        How can it works after I add lines and code in to tree/files ??

        So sir please can you just explain above thing in little bit details..Its very helpful for me so..

        Thanks a lot..
        Regards

        Jaymin D

        • anil_pugalia

          Yes, you can add your source lines – after all it is just a piece of C code. Compilation has to be done from the top directory of the kernel source. If it is built as part of the kernel, then “make” would build it. If it is built as a module, then “make modules” would build it. In the first case, you will have to boot with your new kernel image, thus built. In the second case, you can just load the corresponding driver, thus built.

          And, in case your are interested in monthly updates on related techie stuff, you may register yourself at http://sysplay.in/index.php?pagefile=login

  • Jaymin D

    Hello All,

    please help me to find out the solution that,

    How can I add and compile my custom application code in my kernel ??

    How to add my ‘.c’ ‘.o’ file into my kernel ‘bin’ directory and compiling it ??

    I made hello.c and hello.o file and I want to add these file into my
    kernel such way that when kernel start this hello.o file execute and
    run..

    (If any makefile needed to write then also tell me that how can I do it ???)

    So please give me some idea about it that how can I do it ??

    Please reply me.

    Thanks

    Jaymin D

    • anil_pugalia

      Easiest is to write your code as a driver. And let it load, when kernel boots up, calling the corresponding init of your driver. For details, pick up any getting started with Linux drivers tutorial. You may read the following as well: http://sysplay.in/blog/linux-device-drivers/2013/03/writing-your-first-linux-driver-in-the-classroom/.

      • Jaymin D

        Thanks a very lot sir for your answer and give such a good information..I will see your given link and then I will ask you about doubts if any generate….
        I will ask you…

        thanks a lot..
        regards
        Jaymin D

        • anil_pugalia

          You are welcome.

  • Vijay Kanta

    I emulated the program with my SanDisk Cruzer Blade and my Vodafone data card, but whenever I try to register or info, the usb_storage takes over just after inserting, and dmesg shows no infomation from my programs. What am I doing wrong?

    • anil_pugalia

      Follow the following steps:
      + Insert your device
      + Unload the usb_storage driver using rmmod
      + Load your driver using insmod

      And see, if it helps.

      • Vijay Kanta

        Doesn’t help. This is the output of :~$ lsmod

        usb_storage 40172 0
        usblp 10651 0
        binfmt_misc 6599 1
        snd_intel8x0 25632 2
        snd_ac97_codec 99227 1 snd_intel8x0
        ac97_bus 1014 1 snd_ac97_codec
        i915 290938 2
        snd_pcm 71475 2 snd_intel8x0,snd_ac97_codec
        snd_seq_midi 4588 0
        snd_rawmidi 17783 1 snd_seq_midi
        drm_kms_helper 30200 1 i915
        snd_seq_midi_event 6047 1 snd_seq_midi
        snd_seq 47174 2 snd_seq_midi,snd_seq_midi_event
        snd_timer 19067 2 snd_pcm,snd_seq
        drm 168054 2 i915,drm_kms_helper
        snd_seq_device 5744 3 snd_seq_midi,snd_rawmidi,snd_seq
        ppdev 5556 0
        parport_pc 26058 1
        intel_agp 26360 2 i915
        snd 49006 11 snd_intel8x0,snd_ac97_codec,snd_pcm,snd_rawmidi,snd_seq,snd_timer,snd_seq_device
        i2c_algo_bit 5168 1 i915
        video 18712 1 i915
        soundcore 880 1 snd
        psmouse 59033 0
        shpchp 29886 0
        serio_raw 4022 0
        snd_page_alloc 7120 2 snd_intel8x0,snd_pcm
        agpgart 32011 2 drm,intel_agp
        output 1883 1 video
        lp 7342 0
        parport 31492 3 ppdev,parport_pc,lp
        8139too 19581 0
        8139cp 16934 0
        mii 4425 2 8139too,8139cp

        • anil_pugalia

          Seems okay to me. Do a lsmod after rmmod of usb-storage and insmod of pen_register, and check out for no usb_storage listed there. And I assume, that you have changed the vendor id & device id in the pen_register driver for your device.

          • Vijay Kanta

            Ah, that was it. I didn’t substitute my USB device’s IDs, silly me. Now that it’s done, I see all messages I wrote in my program. Thanks to you. :-)

          • anil_pugalia

            You are welcome.

All published articles are released under Creative Commons Attribution-NonCommercial 3.0 Unported License, unless otherwise noted.
Open Source For You is powered by WordPress, which gladly sits on top of a CentOS-based LEMP stack.

Creative Commons License.