I'm trying to get FT232 serial numbers into my C++ program, to check the
COM port mapping at load time. Starting with libftdi1-1.5.tar.bz2, I
have adapted the example program find_all.c to a function in my program:
#include <libusb-1.0/libusb.h>
#include <libftdi1/ftdi.h> // Nov2024, get serial numbers from COM ports
int FtdiSerialNumbersRead()
{
char mfg[64], dsc[32], s_n[16];
int ret = 0;
bzero(mfg);
bzero(dsc);
bzero(s_n);
//see
https://github.com/particle-iot/libftdi/blob/master/examples/find_all.c
struct ftdi_context* ftdi_p = ftdi_new();
struct ftdi_device_list * devlist_p, *curdev;
int numDevs = ftdi_usb_find_all(ftdi_p, &devlist_p, 0, 0); // send
zeroes for VID and PID so nothing is excluded
curdev = devlist_p;
printf("ftdi_usb_find_all returned %d. Context is %lx. Devlist is
%lx %lx\n", numDevs, ftdi_p, devlist_p->next, devlist_p->dev);
for (int dix = 0; (dix < numDevs) && (NULL != curdev); dix++)
{
//ftdi_p->usb_dev is NULL here, with -4 return values from
ftdi_usb_get_strings[2]()
//type mismatch: ftdi_p->usb_dev = curdev->dev;
struct libusb_device_descriptor descr;
int descRc = libusb_get_device_descriptor(curdev->dev, &descr);
//segfault if ftdi->usb_dev is not set and opened
//int snRc =
libusb_get_string_descriptor_ascii(ftdi_p->usb_dev,
descr.iSerialNumber, (unsigned char *)s_n, sizeof(s_n));
//printf(" libusb_get_string_descriptor_ascii
returned %d [%s]\n", snRc, s_n);
int stringsRc = ftdi_usb_get_strings(ftdi_p, curdev->dev,
mfg, sizeof(mfg),
dsc, sizeof(dsc),
s_n, sizeof(s_n));
printf(" strings: %d [%s] [%s] [%s]\n", stringsRc, mfg, dsc,
s_n);
curdev = curdev->next;
}
return ret;
}
ftdi_usb_get_strings always returns -4, indicating that this happened:
if (ftdi->usb_dev == NULL && libusb_open(dev, &ftdi->usb_dev) < 0)
ftdi_error_return(-4, "libusb_open() failed");
The listing above shows that I tried bypassing ftdi_usb_get_strings and
going straight to ftdi_usb_get_strings2, then started copying lines from
that function until I got a SEGV on libusb_get_string_descriptor_ascii.
I think the key is that libusb_device_handle ftdi->usb_dev is NULL at
call time. I have the libusb_device curdev->dev, but the mapping
between the two isn't obvious.
Should I be plugging curdev->dev into the ftdi context before calling
ftdi_usb_get_strings? The example doesn't show that. What is the
transformation? I hit bottom in libusb.h. The structures are
referenced there but defined elsewhere. How does it tie together?
Thank you.
--
libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
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