I have ported zeptoforth to the nRF52840, based on my port to the nRF52832, which turned out to be extremely similar to it. Unfortunately, I have been unable to run the nRF52840 port on the nRF52840-DONGLE board I now own, because the nRF52840-DONGLE board turns out to include a proprietary bootloader which takes up the space occupied by the exception vectors, which zeptoforth needs to occupy in order to function (as it needs to not only reset but handle IRQ interrupts from a UART). While there are SWD headers on the board, the pads for them are small and I am not good at soldering. As a result, actually testing the nRF52840 port is on hold for now.