Microbian port to XIAO nRF52840

For founding material look at original.README.md

Hardware

I've been working on the cheaper Seeed Studio XIAO nRF52840 without IMU and mic. The expansion board has SWD and an easier to use reset button.

Seeed Studio XIAO nRF52840 (Sense) https://wiki.seeedstudio.com/XIAO_BLE/ has an IMU and microphone

Using Seeed XIAO Expansion board https://wiki.seeedstudio.com/Seeeduino-XIAO-Expansion-Board/

There is also a SAMD21 version https://wiki.seeedstudio.com/Seeeduino-XIAO/ which can be bought with headers pre-soldered. It lacks a reset button so the expansion board is pretty much required although pads are exposed for shorting reset in place of a button.

I thought it was of interest because of my unfinished Adafruit trinket USB microbian port which could benefit from a better approach to adding cdc. And could provide a route for adding Seeed SAMD21 to microbian.

Folders I remember touching or have started.

• x19b-buzzer

• x20-radio - bytes are rx'd and tx'd but it's not fluid, not fully investigated

• x31-adc-battery - hang over from earlier hacking, need fix blocking

• x40-i2crtc - need to clean up api rapid conversion from c++ with search and replace

• x41-tinyusb-prep pre usb-startup.o

• x42b-fromx41 pre usb-startup.o

• x42c-usbserial-driver - "minicom -D /dev/ttyACM1" cat file.txt > /dev/ttyACM1

• x42-testwithout-tinyusb - checking for stability since getting hardfaults

• x43-timerbug - checking for hardfaults, don't have a DAPLINK yet, potential problem inherited from bootloader as Seeed bootloader source closed can't tell if fixed.

• x44-oled - I2C oled driver outside of microbian

• x45-pingpong - oled bouncing ball with buzzer on rebound

TODO:

Finish and clean tinyusb-cdc-lib.a. While it it possible to get away with the no RTOS model most of the time for experimentation it looks like semaphores will need to be implemented. Which goes against the spirit of microbian. But I may get around to adding it as a compile option.

Would blocking usbserial rx be desirable? Currently returns (int)-1 for not available. Would fprintf be a good idea?

investigate radio - have not read datasheet for differences if any from UBITv2

Drivers to make:

• PWM

• SPIM on SPI2

• SPIM on SPI2 with DMA

• QSPI with DMA

• microphone (Sense)

• IMU (Sense)

Probably never: SOFTDEVICE would require usb priority going back down from 0 to 2 and adding semaphore primitive to support that if i've understood things correctly. I'm getting away with -DCFG_TUSB_OS=OPT_OS_NONE and using NVIC priority 0 for USB for early experiments. But it's not robust enough.

Programming

I've not tried the UF2 interface.

For DFU serial. Install Adafruit_nRF52_nrfutil https://github.com/adafruit/Adafruit_nRF52_nrfutil

or pip3 install --user adafruit-nrfutil

Double reset enters DFU bootloader.

I used the toolchain that came with Arduino 1.8.19

Navigate to File > Preferences, and fill "Additional Boards Manager URLs" with the url below:

https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json

Then Navigate to Tools > Board > Boards Manager...,

type the keyword "seeed nrf52" in the search box,

select the latest version of the board you want, and install it. You can install both. The mbed one is much more mature.

Used Seeed arduino ide and board package for hints and the tools chain.

Right now my microbian port is a bit untity but it works. It's untidier than it should be because of getting tinyusb-cdc-lib.a going, but not polished in anyway it's just proof of concept.

I have yet to learn the tinyusb API properly.

If you want tinyusb-cdc-lib.a do the install below. It is however unfinished.

install tinyusb repo and patches with:

"cd baremetal/baremetal-v2-xiao-nrf52/setup-tinyusb/"

"./install-tinyusb-cdc-lib.a.sh"

"../../tinyusb/examples/device/cdc_XIAO_donor/make tinyusb-cdc-lib"

tinyusb will be parallel with baremetal-v2-xiao-nrf2