Why does this FTDI function return zero for the fthandle? - handle

Question

I have a FTDI USB3 development board and some FTDI provided code for accessing it. The code works fine for things like the Device number, VID/PID etc. but always returns zero for the 'ftHandle'. As the handle is required for driving the board, this is not helpful! Can anyone see why this should happen?
static FT_STATUS displayDevicesMethod2(void)
{
FT_STATUS ftStatus;
FT_HANDLE ftHandle = NULL;
// Get and display the list of devices connected
// First call FT_CreateDeviceInfoList to get the number of connected devices.
// Then either call FT_GetDeviceInfoList or FT_GetDeviceInfoDetail to display device
info.
// Device info: Flags (usb speed), device type (600 e.g.), device ID (vendor,
product),
handle for subsequent data access.
DWORD numDevs = 0;
ftStatus = FT_CreateDeviceInfoList(&numDevs); // Build a list and return number
connected.
if (FT_FAILED(ftStatus))
{
printf("Failed to create a device list, status = %d\n", ftStatus);
}
printf("Successfully created a device list.\n\tNumber of connected devices: %d\n",
numDevs);
// Method 2: using FT_GetDeviceInfoDetail
if (!FT_FAILED(ftStatus) && numDevs > 0)
{
ftHandle = NULL;
DWORD Flags = 0;
DWORD Type = 0;
DWORD ID = 0;
char SerialNumber[16] = { 0 };
char Description[32] = { 0 };
for(DWORD i = 0; i <numDevs; i++)
{
ftStatus = FT_GetDeviceInfoDetail(i, &Flags, &Type, &ID, NULL, SerialNumber,
Description, &ftHandle);
if (!FT_FAILED(ftStatus))
{
printf("Device[%d] (using FT_GetDeviceInfoDetail)\n", i);
printf("\tFlags: 0x%x %s | Type: %d | ID: 0x%08X | ftHandle=0x%p\n",
Flags,
Flags & FT_FLAGS_SUPERSPEED? "[USB 3]":
Flags & FT_FLAGS_HISPEED? "[USB 2]":
Flags & FT_FLAGS_OPENED? "[OPENED]": "",
Type,
ID,
ftHandle);
printf("\tSerialNumber=%s\n", SerialNumber);
printf("\tDescription=%s\n", Description);
}
}
}
return ftStatus;
}

Answer 1

This is indeed not super straight forward, but a short peek in the FTDI Knowledgebase yields:
This function builds a device information list and returns the number of D2XX devices connected to the system. The list contains information about both unopen and open devices.
A handle only exists for an opened device. Thus, I assume that your code does not already include that step. If so you need to open it first, e.g. using FT_Open. There are plenty of examples available. You can check their page or stackoverflow for a working example.