USB communication related issue on C5-BTLE

[dsouzahansenfrancis]

To create this issue DEFAULT_EMULATED_DATA_STATUS was enabled. Thereafter when USB port was connected to PC it was found that BLE transfer speeds visibly slowed down.
Removing the USB port caused the BLE transfer to reach its initial transfer speed.
It was also found that issuing an openxc-dump command caused communication to work unaffected simultaneously when BLE and USB were connected.

[peplin]

There's a bit more background on this issue here: https://github.com/openxc/vi-firmware/blob/next/src/platform/pic32/usb.cpp#L114-L118

The short summary is that the USB API for the PIC32 (or at least the way I found to use the API) requires spinning waiting for a handle to be not busy, so if USB is connected but not trying to read data, it will slow down the main loop. There may be a way to use interrupts instead.