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USB Generic HID Device Example Code - Why is this "send" embedded in the receive function?

Question asked by Nick Guzzardo on Sep 28, 2018
Latest reply on Sep 28, 2018 by Hui_Ma

I'm using the LPCXpresso54608 SDK for MCUXpresso.  In particular, I'm running the generic HID device with FreeRTOS example code (link to my code/setup).


The purpose of the code is to echo data sent from a PC program back to the PC.  This all works as intended, but now I'm trying to modify it for my specific application needs.


In the function "USB_DeviceHidGenericCallback", the switch/case called after receiving a USB message includes a call to "USB_DeviceHidSend" which performs the echo function ... so far so good.  After that, within the same switch/case "USB_DeviceHidRecv" which eventually calls "USB_DeviceLpc3511IpRecv" which is the device specific call for the LPCXpresso54608 development board ... again, so far so good.  But then, within "USB_DeviceLpc3511IpRecv", the only function is to call "USB_DeviceLpc3511IpSend".


usb_status_t USB_DeviceLpc3511IpRecv(usb_device_controller_handle controllerHandle,

                                     uint8_t endpointAddress,

                                     uint8_t *buffer,

                                     uint32_t length)


    return USB_DeviceLpc3511IpSend(controllerHandle, endpointAddress, buffer, length);

// Example code echo data???  NBG

//    return kStatus_USB_Success;



My initial thought was that this was simply an accidental redundant means of echoing the received data, but when it is called, no data is received by the PC.  I attempted to replace the call with a return of the enumerated value for a successful USB operation, but then the ENTIRE PROGRAM STOPPED FUNCTIONING AND I HAVE NO IDEA WHY!!!


If anyone knows what the purpose is for the send within the receive shown above, please let me know.


Thank you in advance!