Unplug all other devices connected to your USB ports and try connecting the dongle again.
On older machines: Make sure that you have the correct CDC drivers installed.
Try connecting it to another computer.
Bootloader issues
Bootloader fails to upload image file.
Verify that you are trying to upload a valid image file.
Try if you can upload a different image file.
Make sure you are trying to upload the image file during the time window where the bootloader is open.
Make sure you have closed down anything, like serial communication programs (e. g. TeraTerm or Minicom), that might be connected to the dongle before trying to upload a new image.
For Linux users: Try disabling the modemmanager. As it may lock up the com port for awhile and not leaving enough time to use the boodloader before the main app starts up.
Firmware issues
I have flashed my own firmware but it doesn't start.
Make sure you have changed the crystal setup in custom_config_qpsi.h as the BleuIO doesn’t have a 32KHz crystal:
Change:
#define dg_configUSE_LP_CLK LP_CLK_32768 // 32KHz. Usually the default in most Dialog Semiconductor projects.
to
#define dg_configUSE_LP_CLK LP_CLK_RCX // 16Khz.
