I previously tried combining USBD CDC ACM with 802.15.4 under Softdevice, and this did not work.
Now I try combining examples/peripheral/peripheral/usbd_cdc_acm with the 802.15.4 stack and NO Softdevice. The result is a compilation error. There appears to be a conflict related to power. Specifically, POWER and NRFX_POWER are needed in the usbd_cdc_acm example, so nrfx_power.c is included in the build. What I observe is shown below. What can be done to correct this? The conflict is because the Makefile specifies nrf_802154_clock_nodrv.c, but this conflicts with nrfx_power.c. Maybe the Makefile should change so that the 802.15.4 stack uses another clock source, I am not sure what.
opt/gccarm/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/bin/ld: _build/nrf52840_xxaa/nrf_802154_clock_nodrv.c.o: in function `POWER_CLOCK_IRQHandler': Desktop/nRF52840/SDK15.3/components/802.15.4/src/platform/clock/nrf_802154_clock_nodrv.c:99: multiple definition of `POWER_CLOCK_IRQHandler'; _build/nrf52840_xxaa/nrfx_power.c.o:Desktop/nRF52840/SDK15.3/modules/nrfx/drivers/src/nrfx_power.c:333: first defined here collect2: error: ld returned 1 exit status