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c++ wraper: open(vid,pid) fails for devices with a missing iManufacturer, iProduct or iSerial

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c++ wraper: open(vid,pid) fails for devices with a missing iManufacturer, iProduct or iSerial

Matthias Janke-2
  Hi All,
 
  I'm using the c++ wrapper of libftdi (git co of yesterday) to
  communicate with a FT2232HL on a Lattice XO2 Eval board
  (LCMXO2-7000HE-B-EVN) this board has no programmed in iSerial.
 
  A simple c++ program which just opens and closes the device fails with
  "libusb_get_string_descriptor_ascii() failed" this is also true for
  the find_all_pp example (find_all, works). This failure originates in
  the use of the get_strings() function inside all c++ open() functions.
  This function wants all three iManufractuer, iProduct and iSerial to be
  present. The C-API allows one to pass NULL to ignore these descriptors.
  This is currently not possible with the c++ api. To properly fix this I
  suspect an api break is needed. As temporary ugly workaround I use the
  appended patch. Are there other ideas to fix this?
 
  Cheerio,
  Matthias

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Re: c++ wraper: open(vid,pid) fails for devices with a missing iManufacturer, iProduct or iSerial

Matthias Janke-2
patch was not attached.

Am Fri, 12 May 2017 13:32:50 +0200
schrieb Matthias Janke <[hidden email]>:

>   Hi All,
>  
>   I'm using the c++ wrapper of libftdi (git co of yesterday) to
>   communicate with a FT2232HL on a Lattice XO2 Eval board
>   (LCMXO2-7000HE-B-EVN) this board has no programmed in iSerial.
>  
>   A simple c++ program which just opens and closes the device fails
> with "libusb_get_string_descriptor_ascii() failed" this is also true
> for the find_all_pp example (find_all, works). This failure
> originates in the use of the get_strings() function inside all c++
> open() functions. This function wants all three iManufractuer,
> iProduct and iSerial to be present. The C-API allows one to pass NULL
> to ignore these descriptors. This is currently not possible with the
> c++ api. To properly fix this I suspect an api break is needed. As
> temporary ugly workaround I use the appended patch. Are there other
> ideas to fix this?
>   Cheerio,
>   Matthias
>
> --
> libftdi - see http://www.intra2net.com/en/developer/libftdi for
> details. To unsubscribe send a mail to
> [hidden email]  


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0001-Temporary-workaround-to-make-c-open-funktions-work-w.patch (4K) Download Attachment
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Re: c++ wraper: open(vid,pid) fails for devices with a missing iManufacturer, iProduct or iSerial

Thomas Jarosch
In reply to this post by Matthias Janke-2
Hi Matthias,

Am 12.05.2017 um 13:32 schrieb Matthias Janke:

>   I'm using the c++ wrapper of libftdi (git co of yesterday) to
>   communicate with a FT2232HL on a Lattice XO2 Eval board
>   (LCMXO2-7000HE-B-EVN) this board has no programmed in iSerial.
>  
>   A simple c++ program which just opens and closes the device fails with
>   "libusb_get_string_descriptor_ascii() failed" this is also true for
>   the find_all_pp example (find_all, works). This failure originates in
>   the use of the get_strings() function inside all c++ open() functions.
>   This function wants all three iManufractuer, iProduct and iSerial to be
>   present. The C-API allows one to pass NULL to ignore these descriptors.
>   This is currently not possible with the c++ api. To properly fix this I
>   suspect an api break is needed. As temporary ugly workaround I use the
>   appended patch. Are there other ideas to fix this?

what about this open() function from ftdi.cpp:

int Context::open(int vendor, int product, const std::string&
description, const std::string& serial, unsigned int index)
{
    // translate empty strings to NULL
    // -> do not use them to find the device (vs. require an empty
string to be set in the EEPROM)
    const char* c_description=NULL;
    const char* c_serial=NULL;
    if (!description.empty())
        c_description=description.c_str();
    if (!serial.empty())
        c_serial=serial.c_str();

    int ret = ftdi_usb_open_desc_index(d->ftdi, vendor, product,
c_description, c_serial, index);

    if (ret < 0)
       return ret;

    return get_strings_and_reopen();
}



-> if you pass an empty string for "std::string serial",
it should pass down NULL for the serial parameter of the C API.

What happens if you use this specific open() function?

Cheers,
Thomas

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Re: c++ wraper: open(vid,pid) fails for devices with a missing iManufacturer, iProduct or iSerial

Matthias Janke-2
Hi Thomas,

Am Tue, 23 May 2017 21:26:23 +0200
schrieb Thomas Jarosch <[hidden email]>:

> Hi Matthias,
>
> Am 12.05.2017 um 13:32 schrieb Matthias Janke:
> >   I'm using the c++ wrapper of libftdi (git co of yesterday) to
> >   communicate with a FT2232HL on a Lattice XO2 Eval board
> >   (LCMXO2-7000HE-B-EVN) this board has no programmed in iSerial.
> >  
> >   A simple c++ program which just opens and closes the device fails
> > with "libusb_get_string_descriptor_ascii() failed" this is also
> > true for the find_all_pp example (find_all, works). This failure
> > originates in the use of the get_strings() function inside all c++
> > open() functions. This function wants all three iManufractuer,
> > iProduct and iSerial to be present. The C-API allows one to pass
> > NULL to ignore these descriptors. This is currently not possible
> > with the c++ api. To properly fix this I suspect an api break is
> > needed. As temporary ugly workaround I use the appended patch. Are
> > there other ideas to fix this?  
>
> what about this open() function from ftdi.cpp:
>
> int Context::open(int vendor, int product, const std::string&
> description, const std::string& serial, unsigned int index)
> {
>     // translate empty strings to NULL
>     // -> do not use them to find the device (vs. require an empty
> string to be set in the EEPROM)
>     const char* c_description=NULL;
>     const char* c_serial=NULL;
>     if (!description.empty())
>         c_description=description.c_str();
>     if (!serial.empty())
>         c_serial=serial.c_str();
>
>     int ret = ftdi_usb_open_desc_index(d->ftdi, vendor, product,
> c_description, c_serial, index);
>
>     if (ret < 0)
>        return ret;
>
up to this point everything looks ok. but
this:
>     return get_strings_and_reopen();

innternaly calls get_strings() which unconditioaly tries to get all!
strings:

int Context::get_strings()
 323 {
 324     // Prepare buffers
 325     char vendor[512], desc[512], serial[512];
 326
 327     int ret = ftdi_usb_get_strings(d->ftdi, d->dev, vendor, 512,
desc, 512, serial, 512); 328
 329     if (ret < 0)
 330         return -1;
 331
 332     d->vendor = vendor;
 333     d->description = desc;
 334     d->serial = serial;
 335
 336     return 1;
 337 }

cheers,
Matthias

> }
>
>
>
> -> if you pass an empty string for "std::string serial",  
> it should pass down NULL for the serial parameter of the C API.
>
> What happens if you use this specific open() function?
>
> Cheers,
> Thomas
>
> --
> libftdi - see http://www.intra2net.com/en/developer/libftdi for
> details. To unsubscribe send a mail to
> [hidden email]  


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