zeptoforth

I have added prebuilt images for zeptoforth for the STM32L476, STM32F407, nRF52832, and nRF52840, and prebuilt images including precompiled Forth code for the STM32L476 and STM32F407 (but not the Nordic Semiconductor MCU's, as I need working setups to create these images) to the repository. As a result, one can use zeptoforth without having to build its kernel or its core libraries.

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.

Basing my code off of preexisting code for Mecrisp-Stellaris, I have done a port of zeptoforth to the nRF52832 even though I do not own a board with this MCU. This is largely as a stepping-stone to doing a port to the nRF52840, which I do own but for which no port for Mecrisp-Stellaris exists at this time. If my experience with the STM32L476 and the STM32F407 is any indicator, I expect the port from one Nordic Semiconductor board to another to be relatively painless, specially since they are both in the nRF52 family.

While currently zeptoforth works with STM32L476 and STM32F407 DISCOVERY boards, I am currently waiting for an nRF52840-DONGLE board by Nordic Semiconductor so I can not only port zeptoforth to a board that is not an STMicroelectronics product but also so that I will be able to work with low-power wireless communication, which will be exciting. Unfortunately I was notified that my shipping time may  take longer due to the coronavirus outbreak, so we will see how long it takes for it to reach my doorstep.

[UPDATE: The board has arrived! Now porting can commence.]