Serial Communication with a Garmin Device

[dinesh_pam]

Hi, am new to MS VC++, and I need to interface a PC to a handeheld GPS device (Garmin etrex). Am using a serial to USB cable, and I can connect using hyperterminal so HW is ok. However, when I try to use some example code supplied on the Garmin website, I cant connect! The relevant code fragment is (I believe): HDEVINFO theDevInfo = SetupDiGetClassDevs((GUID*) &GUID_DEVINTERFACE_GRMNUSB, NULL, NULL, DIGCF_ALLCLASSES ); SP_DEVICE_INTERFACE_DATA theInterfaceData; theInterfaceData.cbSize = sizeof( theInterfaceData ); if( !SetupDiEnumDeviceInterfaces( theDevInfo, NULL, (GUID* &GUID_DEVINTERFACE_GRMNUSB, &theInterfaceData ) && GetLastError() == ERROR_NO_MORE_ITEMS ) { gHandle = 0; return; } -------------- Garmin tech support wont help and any help would be GREATLY appreciated :confused: Thanks! Dinesh

[cppcook]

hey man, why do you want to do this? Garmin products have features other than navigation? btw, I have a garmin streetpilot i5 and it works very well.:)

[kitty5]

dinesh_pam wrote:

if( !SetupDiEnumDeviceInterfaces( theDevInfo, NULL, (GUID* &GUID_DEVINTERFACE_GRMNUSB, &theInterfaceData ) && GetLastError() == ERROR_NO_MORE_ITEMS ) { gHandle = 0; return; }

In the above try this so see what the error exactly is: // Find the requested interface if( !SetupDiEnumDeviceInterfaces( theDevInfo, NULL, (GUID* &GUID_DEVINTERFACE_GRMNUSB, &theInterfaceData ) ) { if(GetLastError()== ERROR_NO_MORE_ITEMS) { printf("**Error: couldn't find device(no more items), (0)\n"); SetupDiDestroyDeviceInfoList(theDevInfo); gHandle = 0; return -1; } else { printf("**Error: couldn't enum device, (%d)\n"), GetLastError()); SetupDiDestroyDeviceInfoList(theDevInfo); gHandle = 0; return -1; } } Kitty5

[dinesh_pam]

thank you kindly for the reply. The error is couldnt find device. i.e. "**Error: couldn't find device(no more items), (0)" Is there anyway I could just read the virtual COM port like hyperterminal is doing instead of this? Dinesh

[kitty5]

Not quite sure how to:

dinesh_pam wrote:

Is there anyway I could just read the virtual COM port like hyperterminal is doing instead of this?

However: Did you include the file that contains the device's GUID? It's usually a .h file that looks like: #ifdef DEFINE_GUID // The GUID that is used to identify this device's interface // {AF1B231E-1180-420b-8CB6-2ED2A53F9F92} DEFINE_GUID(GUID_DEVINTERFACE_ALTGENERIC, 0xaf1b231e, 0x1180, 0x420b, 0x8c, 0xb6, 0x2e, 0xd2, 0xa5, 0x3f, 0x9f, 0x92); #endif If you don't have a GUID for your device the PC will not be able to create a handle to the device. The handle is what give you the ability to communicate to the device. Also, make sure that you: #include "INITGUID.H" in that GUID .h file. Kitty5

[dinesh_pam]

Thanks, but all that's done further up in the file. I'm really frustrated with this. I find it hard to believe such a simple task can be so complicated.. Anybody else help me out please?:~ Dinesh

[led mike]

Well your call to SetupDiEnumDeviceInterfaces does not have matching parenthesis so something very wrong is there. You are not checking the HDEVINFO return value so you may not even have a valid handle to pass to SetupDiEnumDeviceInterfaces

HDEVINFO hDevInfoSet = SetupDiGetClassDevs(&guid, NULL, NULL, DIGCF_ALLCLASSES );
if( INVALID_HANDLE_VALUE == hDevInfoSet)
{
DWORD dwErr = ::GetLastError();
// display error information or whatever
}
else
{ ...}

You are not initializing the SP_DEVICE_INTERFACE_DATA structure which is probably not a problem but you never know.

SP_DEVICE_INTERFACE_DATA devInterfaceData = {0};
devInterfaceData.cbSize = sizeof(devInterfaceData);