First time noob - flashing bootloader onto E73-2G4M08S1C nrf52840 modules

[MCorgano]

I'm a complete idiot when it comes to Nordic, this is literally my first time experience with any Nordic chips. I have a little experience programming ESP32-s3 chips, and a lot fo experience with Arduino.

My problem is I ordered E73-2G4M08S1C nrf52840 modules that have no bootloader installed on them, and can't figure out how to program them. I have a few different programmers but do not have a jlink, and I'm not sure what signals I need to see if I have an appropriate alterative. 

My goal is to get the adafruit bootloader / circuit python on it for use with KMK. Once I get circuit python working, I should be able to re-program it no problem, but I need the bootloader first.

MY application is to replace an existing board in a device with my own custom board, so space was at a premium. This is the reason I bought modules instead of dev boards - I have to fit whatever I put on the replacement boards within a 14mm width, and no dev boards I can find will fit this - but the modules do. With the ESP32 I was able to 3d print a jog to hold pogo pins and connect to an FTDI programmer and use their bootstrapping guide to flash it. I can't seem to find similar instructions for Nordic chips.

[Susheel Nuguru]

You have the SWDIO and SWCLK pints on your module.

You just to pull these pins our (using or wire or similar) to be able to connect it to the debugger that supports programming through SWD ports. You can use another nRF52 DK as a programmer to connect the SWD pins to your module to program/debug it.

[MCorgano]

Thankyou for the info! I found a guide somewhere that mentioned using a raspberry pi and open osd (or something like that) to program the bootloader. I do have some spare pi 4s kicking around, so I'm going to try that route. I'll check if any of my dedicated programmers use those connections and check back with what I have available to me.

[MCorgano]

I have had partial success but not quite. I'm trying to get circuit python onto an nRF52840 module that didn't come with a bootloader Module is this https://www.ebyte.com/en/downpdf.aspx?id=445
Same as on this dev board https://circuitpython.org/board/bluemicro840/

Using these instructions I got OpenOSD onto my pi 4, using it for programming and I can write a bootloader and verify it, all appears to work https://github.com/joric/nrfmicro/wiki/Bootloader
Ran the reset run command, plugged it into my computer... and nothing

I swapped out the file they used for the ebyte_e73_tbb_bootloader-0.7.0_s132_6.1.1.hex file from https://github.com/adafruit/Adafruit_nRF52_Bootloader/releases Ran the reset run, plugged it into my laptop..... nothing.

As far as i can tell, the usb connection (used for power while programming as well) going to VBUS, D-, D+, and Gnd, is connected properly. Using the bootloader the guide recommends windows gives a "this device isn't recognized" Using the bootloader from the adafruit page for the E73 (what is engraved on the module itself) and plugging it into windows gives nothing.

Any ideas?

[Susheel Nuguru]

I do not know what is in those hex files of bootloaders and how they should work, . Probably someone else in this forum might know about these external tools and libraries