Hi Thomas,
Am Tue, 23 May 2017 21:26:23 +0200
schrieb Thomas Jarosch <thomas.jarosch@xxxxxxxxxxxxx>:
> 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
>
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