pyusb-users

[pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Jay A. <jay...@gm...>]

Hi,

I am a user of pyOCD, and I am having an issue related to pyusb which
is what the former uses for talking to the USB device. The situation
is that I need to use pyOCD through an eclipse plugin. Eclipse
launches pyocd-gdbserver and normal user. But it will only work if
launched as root.

My question is, how can I make pysb do its job without requiring root
permissions? Here is the error I get when launching pyocd-gdbserver as
normal user. The last lines suggests its pyusb having issues:

uncaught exception: The device has no langid
Traceback (most recent call last):
  File "build/bdist.linux-x86_64/egg/pyOCD/tools/gdb_server.py", line
262, in run
    frequency=self.args.frequency)
  File "build/bdist.linux-x86_64/egg/pyOCD/board/mbed_board.py", line
210, in chooseBoard
    target_override, frequency)
  File "build/bdist.linux-x86_64/egg/pyOCD/board/mbed_board.py", line
182, in getAllConnectedBoards
    connected_daps = dap_class.get_connected_devices()
  File "build/bdist.linux-x86_64/egg/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py",
line 352, in get_connected_devices
    all_interfaces = _get_interfaces()
  File "build/bdist.linux-x86_64/egg/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py",
line 44, in _get_interfaces
    return INTERFACE[usb_backend].getAllConnectedInterface()
  File "build/bdist.linux-x86_64/egg/pyOCD/pyDAPAccess/interface/pyusb_backend.py",
line 88, in getAllConnectedInterface
    product = board.product
  File "/usr/lib/python2.7/site-packages/usb/core.py", line 841, in product
    self._product = util.get_string(self, self.iProduct)
  File "/usr/lib/python2.7/site-packages/usb/util.py", line 314, in get_string
    raise ValueError("The device has no langid")
ValueError: The device has no langid


Please let me know if there are any workarounds to make pyusb work
without requiring root privilege.

-- 

Thanks and Regards,
Aurabindo J

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Steven M. <smi...@gm...>]

Permissions deal with your Linux configuration.

Here is a general answer for Linux.
http://unix.stackexchange.com/questions/44308/understanding-udev-rules-and-permissions-in-libusb

You can google for libusb permissions for your distribution if this doesn't lead to a solution.



> On Aug 20, 2016, at 07:46, Jay Aurabind <jay...@gm...> wrote:
> 
> Hi,
> 
> I am a user of pyOCD, and I am having an issue related to pyusb which
> is what the former uses for talking to the USB device. The situation
> is that I need to use pyOCD through an eclipse plugin. Eclipse
> launches pyocd-gdbserver and normal user. But it will only work if
> launched as root.
> 
> My question is, how can I make pysb do its job without requiring root
> permissions? Here is the error I get when launching pyocd-gdbserver as
> normal user. The last lines suggests its pyusb having issues:
> 
> uncaught exception: The device has no langid
> Traceback (most recent call last):
>  File "build/bdist.linux-x86_64/egg/pyOCD/tools/gdb_server.py", line
> 262, in run
>    frequency=self.args.frequency)
>  File "build/bdist.linux-x86_64/egg/pyOCD/board/mbed_board.py", line
> 210, in chooseBoard
>    target_override, frequency)
>  File "build/bdist.linux-x86_64/egg/pyOCD/board/mbed_board.py", line
> 182, in getAllConnectedBoards
>    connected_daps = dap_class.get_connected_devices()
>  File "build/bdist.linux-x86_64/egg/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py",
> line 352, in get_connected_devices
>    all_interfaces = _get_interfaces()
>  File "build/bdist.linux-x86_64/egg/pyOCD/pyDAPAccess/dap_access_cmsis_dap.py",
> line 44, in _get_interfaces
>    return INTERFACE[usb_backend].getAllConnectedInterface()
>  File "build/bdist.linux-x86_64/egg/pyOCD/pyDAPAccess/interface/pyusb_backend.py",
> line 88, in getAllConnectedInterface
>    product = board.product
>  File "/usr/lib/python2.7/site-packages/usb/core.py", line 841, in product
>    self._product = util.get_string(self, self.iProduct)
>  File "/usr/lib/python2.7/site-packages/usb/util.py", line 314, in get_string
>    raise ValueError("The device has no langid")
> ValueError: The device has no langid
> 
> 
> Please let me know if there are any workarounds to make pyusb work
> without requiring root privilege.
> 
> -- 
> 
> Thanks and Regards,
> Aurabindo J
> 
> ------------------------------------------------------------------------------
> _______________________________________________
> pyusb-users mailing list
> pyu...@li...
> https://lists.sourceforge.net/lists/listinfo/pyusb-users

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Tormod V. <lis...@gm...>]

On Sat, Aug 20, 2016 at 3:46 PM, Steven Michalske wrote:
> Here is a general answer for Linux.
> http://unix.stackexchange.com/questions/44308/understanding-udev-rules-and-permissions-in-libusb

IMHO that link doesn't have the greatest answer (or question).
Probably the asking user failed to use group permission because he
didn't log out and in again after adding the user to the groups. I
think group permissions are superior to just letting any user (or
process) full access to the device. I'd recommend something like this:

# Example udev rules (usually placed in /etc/udev/rules.d)
# Makes given device writeable for the "plugdev" group
ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="0483",
ATTRS{idProduct}=="df11", MODE="664", GROUP="plugdev"

>> On Aug 20, 2016, at 07:46, Jay Aurabind  wrote:
>> I am a user of pyOCD, and I am having an issue related to pyusb which
>> is what the former uses for talking to the USB device. The situation
>> is that I need to use pyOCD through an eclipse plugin. Eclipse
>> launches pyocd-gdbserver and normal user. But it will only work if
>> launched as root.

>> ValueError: The device has no langid

The missing langid here looks like https://github.com/walac/pyusb/issues/139

I don't know if this is something wrong about langid (in the device or
software) or if it is just that requesting langid is the first
operation requiring full access to the device. The last comment there
about specifying langid hints to the former option.

Regards,
Tormod

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Jay A. <jay...@gm...>]

On 20 August 2016 at 21:53, Tormod Volden <lis...@gm...> wrote:
> On Sat, Aug 20, 2016 at 3:46 PM, Steven Michalske wrote:
>> Here is a general answer for Linux.
>> http://unix.stackexchange.com/questions/44308/understanding-udev-rules-and-permissions-in-libusb
>
> IMHO that link doesn't have the greatest answer (or question).
> Probably the asking user failed to use group permission because he
> didn't log out and in again after adding the user to the groups. I
> think group permissions are superior to just letting any user (or
> process) full access to the device. I'd recommend something like this:
>
> # Example udev rules (usually placed in /etc/udev/rules.d)
> # Makes given device writeable for the "plugdev" group
> ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="0483",
> ATTRS{idProduct}=="df11", MODE="664", GROUP="plugdev"
>
>>> On Aug 20, 2016, at 07:46, Jay Aurabind  wrote:
>>> I am a user of pyOCD, and I am having an issue related to pyusb which
>>> is what the former uses for talking to the USB device. The situation
>>> is that I need to use pyOCD through an eclipse plugin. Eclipse
>>> launches pyocd-gdbserver and normal user. But it will only work if
>>> launched as root.
>
>>> ValueError: The device has no langid
>
> The missing langid here looks like https://github.com/walac/pyusb/issues/139
>
> I don't know if this is something wrong about langid (in the device or
> software) or if it is just that requesting langid is the first
> operation requiring full access to the device. The last comment there
> about specifying langid hints to the former option.
>
> Regards,
> Tormod
>
> ------------------------------------------------------------------------------
> _______________________________________________
> pyusb-users mailing list
> pyu...@li...
> https://lists.sourceforge.net/lists/listinfo/pyusb-users

Hi Tormod and Steve,

Thanks for your responses. I tried running the pyocd-gdbserver with
LIBUSB_DEBUG=9, and got the following[snipped]:

libusb: debug [libusb_open] open 2.1
libusb: error [_get_usbfs_fd] libusb couldn't open USB device
/dev/bus/usb/002/001: Permission denied
libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.
libusb: debug [libusb_open] open 2.1 returns -3
uncaught exception: The device has no langid
Traceback (most recent call last):

The device 1 on bus 2, is actually the root hub - the output of lsusb
-v -s2:1 is:

Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            9 Hub
  bDeviceSubClass         0
  bDeviceProtocol         0 Full speed (or root) hub
  bMaxPacketSize0        64
  idVendor           0x1d6b Linux Foundation
  idProduct          0x0002 2.0 root hub
  bcdDevice            4.06
  iManufacturer           3 Linux 4.6.6-300.fc24.x86_64 ehci_hcd
  iProduct                2 EHCI Host Controller
  iSerial                 1 0000:00:1d.0
  bNumConfigurations      1

But even after adding the following rule to udev, I am still getting
the permission error:

ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="1d6b",
ATTRS{idProduct}=="0003", MODE="0666", GROUP="plugdev"
ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="0d28",
ATTRS{idProduct}=="0204", MODE="0666", GROUP="plugdev"

I tried with both with and without GROUP="plugdev" because the group
didnt really exist in my (Fedora 24) distro. Although I created the
group and added myself to it, and rebooted.

-- 

Thanks and Regards,
Aurabindo J

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Tormod V. <lis...@gm...>]

On Mon, Aug 22, 2016 at 8:19 AM, Jay Aurabind wrote:
> Hi Tormod and Steve,
>
> Thanks for your responses. I tried running the pyocd-gdbserver with
> LIBUSB_DEBUG=9, and got the following[snipped]:
>
> libusb: debug [libusb_open] open 2.1
> libusb: error [_get_usbfs_fd] libusb couldn't open USB device
> /dev/bus/usb/002/001: Permission denied
> libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.
> libusb: debug [libusb_open] open 2.1 returns -3
> uncaught exception: The device has no langid
> Traceback (most recent call last):
>
> The device 1 on bus 2, is actually the root hub - the output of lsusb
> -v -s2:1 is:

I am a bit confused here, did you really want to manipulate the root
hub with pyusb, or did something go wrong here?

>
> Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
> Device Descriptor:
>   bLength                18
>   bDescriptorType         1
>   bcdUSB               2.00
>   bDeviceClass            9 Hub
>   bDeviceSubClass         0
>   bDeviceProtocol         0 Full speed (or root) hub
>   bMaxPacketSize0        64
>   idVendor           0x1d6b Linux Foundation
>   idProduct          0x0002 2.0 root hub
>   bcdDevice            4.06
>   iManufacturer           3 Linux 4.6.6-300.fc24.x86_64 ehci_hcd
>   iProduct                2 EHCI Host Controller
>   iSerial                 1 0000:00:1d.0
>   bNumConfigurations      1

(Obviously the underlying hardware was not made by the Linux
Foundation, the kernel usb stack just presents the root hub like it
would be yet another USB device.)

A "device" like this will be grabbed by the kernel (ehci_hcd driver).
More generally it can happen per USB interface of the device and each
can be claimed by its own driver.

The same would be the case for e.g. a USB mass storage device. The
relevant kernel driver will grab it exclusively, and you won't get
permissions to write to it, whatever the file permissions on the
corresponding USB device node.

Some devices can be released from the kernel, and then be available
for you to manipulate it through the device node (and thus via e.g
libusb and pyusb). See for instance the libusb_detach_kernel_driver()
function in libusb. However, in most cases people use libusb and pyusb
to access devices that have no kernel driver.

> But even after adding the following rule to udev, I am still getting
> the permission error:
>
> ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="1d6b",
> ATTRS{idProduct}=="0003", MODE="0666", GROUP="plugdev"
> ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="0d28",
> ATTRS{idProduct}=="0204", MODE="0666", GROUP="plugdev"
>
> I tried with both with and without GROUP="plugdev" because the group
> didnt really exist in my (Fedora 24) distro. Although I created the
> group and added myself to it, and rebooted.

(You can of course use any group that you are member of.)

Regards,
Tormod

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Jay A. <jay...@gm...>]

On 23 August 2016 at 02:18, Tormod Volden <lis...@gm...> wrote:
> On Mon, Aug 22, 2016 at 8:19 AM, Jay Aurabind wrote:
>> Hi Tormod and Steve,
>>
>> Thanks for your responses. I tried running the pyocd-gdbserver with
>> LIBUSB_DEBUG=9, and got the following[snipped]:
>>
>> libusb: debug [libusb_open] open 2.1
>> libusb: error [_get_usbfs_fd] libusb couldn't open USB device
>> /dev/bus/usb/002/001: Permission denied
>> libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.
>> libusb: debug [libusb_open] open 2.1 returns -3
>> uncaught exception: The device has no langid
>> Traceback (most recent call last):
>>
>> The device 1 on bus 2, is actually the root hub - the output of lsusb
>> -v -s2:1 is:
>
> I am a bit confused here, did you really want to manipulate the root
> hub with pyusb, or did something go wrong here?
>

Absolutely not, only reason I wanted to try giving write permission to
that device, which happens to be the root hub was because that's the
only permission error I see in the LIBUSB debug messages, as you can
see from the logs I showed. If I run pyusb as root, I do not see those
permission errors.

I suspect that pyusb reads certain data commonly for all available
devices, may to figure out whether that is really the device it needs
to work on ?

>>
>> Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
>> Device Descriptor:
>>   bLength                18
>>   bDescriptorType         1
>>   bcdUSB               2.00
>>   bDeviceClass            9 Hub
>>   bDeviceSubClass         0
>>   bDeviceProtocol         0 Full speed (or root) hub
>>   bMaxPacketSize0        64
>>   idVendor           0x1d6b Linux Foundation
>>   idProduct          0x0002 2.0 root hub
>>   bcdDevice            4.06
>>   iManufacturer           3 Linux 4.6.6-300.fc24.x86_64 ehci_hcd
>>   iProduct                2 EHCI Host Controller
>>   iSerial                 1 0000:00:1d.0
>>   bNumConfigurations      1
>
> (Obviously the underlying hardware was not made by the Linux
> Foundation, the kernel usb stack just presents the root hub like it
> would be yet another USB device.)
>
> A "device" like this will be grabbed by the kernel (ehci_hcd driver).
> More generally it can happen per USB interface of the device and each
> can be claimed by its own driver.
>
> The same would be the case for e.g. a USB mass storage device. The
> relevant kernel driver will grab it exclusively, and you won't get
> permissions to write to it, whatever the file permissions on the
> corresponding USB device node.
>
> Some devices can be released from the kernel, and then be available
> for you to manipulate it through the device node (and thus via e.g
> libusb and pyusb). See for instance the libusb_detach_kernel_driver()
> function in libusb. However, in most cases people use libusb and pyusb
> to access devices that have no kernel driver.

In that case, even the root should not be able to write to those
devices, since its exclusively managed by kernel. Then how come I get
no errors when I run pyocd with root permissions ?

>
>> But even after adding the following rule to udev, I am still getting
>> the permission error:
>>
>> ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="1d6b",
>> ATTRS{idProduct}=="0003", MODE="0666", GROUP="plugdev"
>> ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="0d28",
>> ATTRS{idProduct}=="0204", MODE="0666", GROUP="plugdev"
>>
>> I tried with both with and without GROUP="plugdev" because the group
>> didnt really exist in my (Fedora 24) distro. Although I created the
>> group and added myself to it, and rebooted.
>
> (You can of course use any group that you are member of.)
>
> Regards,
> Tormod
>
> ------------------------------------------------------------------------------
> _______________________________________________
> pyusb-users mailing list
> pyu...@li...
> https://lists.sourceforge.net/lists/listinfo/pyusb-users



-- 

Thanks and Regards,
Aurabindo J

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Tormod V. <lis...@gm...>]

On Tue, Aug 23, 2016 at 8:31 AM, Jay Aurabind wrote:
> On 23 August 2016 at 02:18, Tormod Volden wrote:
>> I am a bit confused here, did you really want to manipulate the root
>> hub with pyusb, or did something go wrong here?
>>
>
> Absolutely not, only reason I wanted to try giving write permission to
> that device, which happens to be the root hub was because that's the
> only permission error I see in the LIBUSB debug messages, as you can
> see from the logs I showed. If I run pyusb as root, I do not see those
> permission errors.

OK, I see.

>
> I suspect that pyusb reads certain data commonly for all available
> devices, may to figure out whether that is really the device it needs
> to work on ?

It usually shouldn't try to retrieve descriptor strings from other
devices than the ones targeted. The device descriptor (retrieved and
cached by the OS) is usually enough to filter out the right devices
(e.g. filtering on vid/pid). How are the devices filtered in your
program?

>> Some devices can be released from the kernel, and then be available
>> for you to manipulate it through the device node (and thus via e.g
>> libusb and pyusb). See for instance the libusb_detach_kernel_driver()
>> function in libusb. However, in most cases people use libusb and pyusb
>> to access devices that have no kernel driver.
>
> In that case, even the root should not be able to write to those
> devices, since its exclusively managed by kernel. Then how come I get
> no errors when I run pyocd with root permissions ?

You won't be able to claim any of its interfaces, but I suppose some
control transfers are still allowed.

Tormod

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Jay A. <jay...@gm...>]

On 23 August 2016 at 16:40, Tormod Volden <lis...@gm...> wrote:
> On Tue, Aug 23, 2016 at 8:31 AM, Jay Aurabind wrote:
>> On 23 August 2016 at 02:18, Tormod Volden wrote:
>>> I am a bit confused here, did you really want to manipulate the root
>>> hub with pyusb, or did something go wrong here?
>>>
>>
>> Absolutely not, only reason I wanted to try giving write permission to
>> that device, which happens to be the root hub was because that's the
>> only permission error I see in the LIBUSB debug messages, as you can
>> see from the logs I showed. If I run pyusb as root, I do not see those
>> permission errors.
>
> OK, I see.
>
>>
>> I suspect that pyusb reads certain data commonly for all available
>> devices, may to figure out whether that is really the device it needs
>> to work on ?
>
> It usually shouldn't try to retrieve descriptor strings from other
> devices than the ones targeted. The device descriptor (retrieved and
> cached by the OS) is usually enough to filter out the right devices
> (e.g. filtering on vid/pid). How are the devices filtered in your
> program?

Here is the code which creates the error:

        all_devices = usb.core.find(find_all=True)

        if not all_devices:
            logging.debug("No device connected")
            return []

        boards = []

        # iterate on all devices found
        for board in all_devices:
            interface_number = -1
            try:
                # The product string is read over USB when accessed.
                # This can cause an exception to be thrown if the device
                # is malfunctioning.
                product = board.product

This is how pyusb is used. The program doesn't go beyond the last line
shown above, if run as normal user. See full source github[1].




[1]:https://github.com/mbedmicro/pyOCD/blob/master/pyOCD/pyDAPAccess/interface/pyusb_backend.py#L88

>
>>> Some devices can be released from the kernel, and then be available
>>> for you to manipulate it through the device node (and thus via e.g
>>> libusb and pyusb). See for instance the libusb_detach_kernel_driver()
>>> function in libusb. However, in most cases people use libusb and pyusb
>>> to access devices that have no kernel driver.
>>
>> In that case, even the root should not be able to write to those
>> devices, since its exclusively managed by kernel. Then how come I get
>> no errors when I run pyocd with root permissions ?
>
> You won't be able to claim any of its interfaces, but I suppose some
> control transfers are still allowed.
>
> Tormod
>
> ------------------------------------------------------------------------------
> _______________________________________________
> pyusb-users mailing list
> pyu...@li...
> https://lists.sourceforge.net/lists/listinfo/pyusb-users



-- 

Thanks and Regards,
Aurabindo J

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Tormod V. <lis...@gm...>]

On Tue, Aug 23, 2016 at 3:02 PM, Jay Aurabind wrote:
> On 23 August 2016 at 16:40, Tormod Volden wrote:
>> It usually shouldn't try to retrieve descriptor strings from other
>> devices than the ones targeted. The device descriptor (retrieved and
>> cached by the OS) is usually enough to filter out the right devices
>> (e.g. filtering on vid/pid). How are the devices filtered in your
>> program?
>
> Here is the code which creates the error:
>
>         all_devices = usb.core.find(find_all=True)
>
>         if not all_devices:
>             logging.debug("No device connected")
>             return []
>
>         boards = []
>
>         # iterate on all devices found
>         for board in all_devices:
>             interface_number = -1
>             try:
>                 # The product string is read over USB when accessed.
>                 # This can cause an exception to be thrown if the device
>                 # is malfunctioning.
>                 product = board.product
>
> This is how pyusb is used. The program doesn't go beyond the last line
> shown above, if run as normal user. See full source github[1].

There is a grave mismatch between comment and code here:

# find all devices matching the vid/pid specified
 all_devices = usb.core.find(find_all=True)

There is nothing in the code that filters on vid/pid.
usb.core.find(find_all=True) will return all devices the OS know of.
Then the code goes on to request the product string from all these
devices... It can be expected that this goes wrong on devices for
which the user has no permissions.

>
> [1]:https://github.com/mbedmicro/pyOCD/blob/master/pyOCD/pyDAPAccess/interface/pyusb_backend.py#L88
>
>>
>>>> Some devices can be released from the kernel, and then be available
>>>> for you to manipulate it through the device node (and thus via e.g
>>>> libusb and pyusb). See for instance the libusb_detach_kernel_driver()
>>>> function in libusb. However, in most cases people use libusb and pyusb
>>>> to access devices that have no kernel driver.
>>>
>>> In that case, even the root should not be able to write to those
>>> devices, since its exclusively managed by kernel. Then how come I get
>>> no errors when I run pyocd with root permissions ?
>>
>> You won't be able to claim any of its interfaces, but I suppose some
>> control transfers are still allowed.

The pyocd code actually goes on to detach any kernel driver (line
111). This might succeed if it is run by root (or user with sufficient
permissions).

Tormod

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Jay A. <jay...@gm...>]

On 23 August 2016 at 18:32, Jay Aurabind <jay...@gm...> wrote:
> On 23 August 2016 at 16:40, Tormod Volden <lis...@gm...> wrote:
>> On Tue, Aug 23, 2016 at 8:31 AM, Jay Aurabind wrote:
>>> On 23 August 2016 at 02:18, Tormod Volden wrote:
>>>> I am a bit confused here, did you really want to manipulate the root
>>>> hub with pyusb, or did something go wrong here?
>>>>
>>>
>>> Absolutely not, only reason I wanted to try giving write permission to
>>> that device, which happens to be the root hub was because that's the
>>> only permission error I see in the LIBUSB debug messages, as you can
>>> see from the logs I showed. If I run pyusb as root, I do not see those
>>> permission errors.
>>
>> OK, I see.
>>
>>>
>>> I suspect that pyusb reads certain data commonly for all available
>>> devices, may to figure out whether that is really the device it needs
>>> to work on ?
>>
>> It usually shouldn't try to retrieve descriptor strings from other
>> devices than the ones targeted. The device descriptor (retrieved and
>> cached by the OS) is usually enough to filter out the right devices
>> (e.g. filtering on vid/pid). How are the devices filtered in your
>> program?
>
> Here is the code which creates the error:
>
>         all_devices = usb.core.find(find_all=True)
>
>         if not all_devices:
>             logging.debug("No device connected")
>             return []
>
>         boards = []
>
>         # iterate on all devices found
>         for board in all_devices:
>             interface_number = -1
>             try:
>                 # The product string is read over USB when accessed.
>                 # This can cause an exception to be thrown if the device
>                 # is malfunctioning.
>                 product = board.product
>
> This is how pyusb is used. The program doesn't go beyond the last line
> shown above, if run as normal user. See full source github[1].
>
>
>
>
> [1]:https://github.com/mbedmicro/pyOCD/blob/master/pyOCD/pyDAPAccess/interface/pyusb_backend.py#L88
>

I just managed to get it working. Simply added an exception for the
try block for ValueError: continue

Is this an acceptable solution generally? Is there a point in asking
pyOCD to take it ?


>>
>>>> Some devices can be released from the kernel, and then be available
>>>> for you to manipulate it through the device node (and thus via e.g
>>>> libusb and pyusb). See for instance the libusb_detach_kernel_driver()
>>>> function in libusb. However, in most cases people use libusb and pyusb
>>>> to access devices that have no kernel driver.
>>>
>>> In that case, even the root should not be able to write to those
>>> devices, since its exclusively managed by kernel. Then how come I get
>>> no errors when I run pyocd with root permissions ?
>>
>> You won't be able to claim any of its interfaces, but I suppose some
>> control transfers are still allowed.
>>
>> Tormod
>>
>> ------------------------------------------------------------------------------
>> _______________________________________________
>> pyusb-users mailing list
>> pyu...@li...
>> https://lists.sourceforge.net/lists/listinfo/pyusb-users
>
>
>
> --
>
> Thanks and Regards,
> Aurabindo J



-- 

Thanks and Regards,
Aurabindo J

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Tormod V. <lis...@gm...>]

On Tue, Aug 23, 2016 at 3:05 PM, Jay Aurabind wrote:
>
> I just managed to get it working. Simply added an exception for the
> try block for ValueError: continue
>
> Is this an acceptable solution generally? Is there a point in asking
> pyOCD to take it ?

I would try to filter on vid/pid first. Are there many different
vid/pids possible, but they all have "CMSIS-DAP" in the product
string?

IMO manually filtering through the product string is a bad idea, but
if it cannot be avoided, yes, you should an exception for devices
where you can't retrieve the product string.

Try for instance "lsusb -v" versus "sudo lsusb -v" - a normal user
will often not see the product strings listed, whereas the superuser
does.

Regards,
Tormod

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Jay A. <jay...@gm...>]

On 23 August 2016 at 21:08, Tormod Volden <lis...@gm...> wrote:
> On Tue, Aug 23, 2016 at 3:05 PM, Jay Aurabind wrote:
>>
>> I just managed to get it working. Simply added an exception for the
>> try block for ValueError: continue
>>
>> Is this an acceptable solution generally? Is there a point in asking
>> pyOCD to take it ?
>
> I would try to filter on vid/pid first. Are there many different
> vid/pids possible, but they all have "CMSIS-DAP" in the product
> string?
>

I'm not sure if that can be generalized. The actual name it shows is
"DAPLink CMSIS-DAP". Unless the debug adapter is running the DAPLink
firmware[1], which is an open source project[2], this name can could
be anything else. The device I am connecting to, is a baseboard for
Hexiwear which has an OpenSDA debug port, which happens to have
support for running DAPLink firmware.


[1]:https://developer.mbed.org/handbook/DAPLink
[2]:https://github.com/mbedmicro/DAPLink

> IMO manually filtering through the product string is a bad idea, but
> if it cannot be avoided, yes, you should an exception for devices
> where you can't retrieve the product string.
>

Looks like that is quickest hack to get it fixed until pyOCD devs
figure out a proper way to do it.

I'm gonna add these 3 lines right after 88 and request them to take it:

except ValueError:
                if board.idVendor is 0xd28 and board.idProduct is 0x204:
                    continue



> Try for instance "lsusb -v" versus "sudo lsusb -v" - a normal user
> will often not see the product strings listed, whereas the superuser
> does.
>
> Regards,
> Tormod
>
> ------------------------------------------------------------------------------
> _______________________________________________
> pyusb-users mailing list
> pyu...@li...
> https://lists.sourceforge.net/lists/listinfo/pyusb-users



-- 

Thanks and Regards,
Aurabindo J

Re: [pyusb-users] pyusb and root permissions "ValueError: The device has no langid"

[Karl P. <ka...@tw...>]

Tormod Volden <lis...@gm...> wrote:
> On Tue, Aug 23, 2016 at 3:05 PM, Jay Aurabind wrote:
> >
> > I just managed to get it working. Simply added an exception for the
> > try block for ValueError: continue
> >
> > Is this an acceptable solution generally? Is there a point in asking
> > pyOCD to take it ?
> 
> I would try to filter on vid/pid first. Are there many
> different vid/pids possible, but they all have "CMSIS-DAP" in
> the product string?
> 
> IMO manually filtering through the product string is a bad
> idea, but if it cannot be avoided, yes, you should an exception
> for devices where you can't retrieve the product string.

yeah, well, would be good to tell ARM that. A device class or
interface class or anything, but no, by definition, a CMSIS-DAP
device is identified _only_ by the product string containing
"CMSIS-DAP"

Thanks ARM!