Some of the registers in USBD cannot be accessed in specific conditions.
This may be the case when USBD is not enabled (using the ENABLE register) and ready (signalled by the READY bit in EVENTCAUSE after a USBEVENT event), or when USBD is in Low-power mode while the USB bus is suspended.
Triggering any tasks, including the tasks triggered through the PPI, is affected by this
behavior. In addition, the following registers are affected:
- HALTED.EPIN[0..7]
- HALTED.EPOUT[0..7]
- USBADDR
- BMREQUESTTYPE
- BREQUEST
- WVALUEL
- WVALUEH
- WINDEXL
- WINDEXH
- WLENGTHL
- WLENGTHH
- SIZE.EPOUT[0..7]
- SIZE.ISOOUT
- USBPULLUP
- DTOGGLE
- EPINEN
- EPOUTEN
- EPSTALL
- ISOSPLIT
- FRAMECNTR