Best way to control EP data send flow (ACK/NACK)?

[GrantMTG]

Best way to control EP data send flow (ACK/NACK)?

[GrantMTG]

I think I have a workable solution. I removed any data activities from the "usbd_evt_eptx" Endpoint Event callback (what you called hid_mouse_move() in the demo and what I call hid_endpoint_eventCb() ). In it's place I just set a flag that tells the application when it is safe to write more data to the HID IN Endpoint.

So now the callback looks like:

static void hid_endpoint_event_Cb(usbd_device *dev, uint8_t event, uint8_t ep)
{
switch(event)
   {
   case usbd_evt_sof:                 // Not supported by core at this time.
        break;

   case usbd_evt_eptx:                 // Data packet transmit complete.
        if(ep == IN_EP1)               // In my case HID is on EP1 IN (there is no CDC)
           {
           if(bLoadEp1 == 0)
              bLoadEp1 = 1;            // Tell main code that we are ready for more.
           }
        break;

   default:
        break;
   }
}

And in the main code:

 if(bLoadEp1)
   {
   bLoadEp1 = 0;                    // Note that it has been sent.
   usbd_ep_write(&udev, HID_RPT_EP, &hid_report_data, EP1_PACKET_SIZE);
   }

Note that this section in the main code only runs if there is actual data to send. This way the Endpoint is NAKing any time there is nothing to send to the host.