Over the air update with MCU Boot?

[vChavezB]

I find the mcuboot bootloader quite nice to do device firmware upgrade (DFU) as it works out of the box (most of the time..).

I was wondering if there are any plans to do OTA as its quite convenient to update the firmware without having to connect a programmer.

An external flash could also be added such as the ones from renesas that consume ~0.2 uA in ultra sleep mode.

[jakkra]

Hi, yes doing OTA is quite simple with MCUBoot, the problem is that I don't have enough flash in the current variant (internal only). For this I need an external flash. It's a bit tight on the PCB right now, but I have a plan how to handle it by replacing charging stuff with an npm1300 and then a flash should fit. However I don't think I'll do this in a while. I also want external flash in order to store more resources such as images etc. on it.

[vChavezB]

About the size constraints, you could easily go as small as 1.7 x 1.7 mm with a WLCSP package. For example the AT25FF161A-MAHN-T is a 2 MB Flash from renesas with 30uA standby , 7nA (ultra sleep).

https://www.mouser.de/ProductDetail/Renesas-Dialog/AT25FF161A-MAHN-T?qs=IS%252B4QmGtzzomVXSM%252BgO0kg%3D%3D

This is how it would look with the 3x2 mm package UDFN

Just need to connect 4 pins (SI,SO,CLK,CS) from the ublox nrf SoC.

If I have some spare time I can add the flash and add the software/hardware changes to test if it works.

[jakkra]

Yeah that could possibly fit if it's possible to route out the 4 pins needed.
Hand soldering/placing WLCSP may be problemetic, I have never dared to try. But feel free to try :)

In the end I'd want a bigger flash, like 8MB or even 16MB to never have issue with flash even with lot's of high res images.
I want to do a PCB change to use a battery manager IC (nPM1300) and fit a flash of this size, but I don't know when, could be some time later this year maybe.

[vChavezB]

Well I did a quick search and some of the flash memory >=4MB have a package of at least 5x6mm which might be more difficult to place with the current PCB. Do you think its possible to put the flash on the bottom layer as I see there is more space but I do not know in detail if it will interfere with vias or other components.

Any case even just as a test with the 2MB flash, the only thing that would need to be changed is the footprint. Luckily there is a generic spi nor driver that is mostly compatible with other flash memories 👍

I will try to do the layout with the 2MB :)

[jakkra]

Yeah that is what I found also, bigger memory => bigger physical size :)
For solderability I want to keep everything on top for now, but I'm sure with some changes a flash will fit.
Please give it a try, sounds good! I should do a full BOM breakdown also, as that is useful for getting all components, will do that some day soon-ish.

[vChavezB]

Regarding the software, I compiled the project and got the following results:

Main branch

App Core

Memory region         Used Size  Region Size  %age Used
           FLASH:      839500 B       984 KB     83.32%
             RAM:      167084 B       448 KB     36.42%
        IDT_LIST:          0 GB         2 KB      0.00%

Log: https://git.fh-aachen.de/vc9917e/ZSWatch/-/jobs/408360/raw

MCUBOOT modifications

After adding mcuboot as a child image of the application core, the image does not fit anymore :/

MCUBoot child image of App Core

Memory region         Used Size  Region Size  %age Used
           FLASH:       43320 B        48 KB     88.13%
             RAM:       26592 B       440 KB      5.90%
        IDT_LIST:          0 GB         2 KB      0.00%

App Core

/workdir/zephyr-sdk/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.2.0/../../../../arm-zephyr-eabi/bin/ld.bfd: region `FLASH' overflowed by 370980 bytes
collect2: error: ld returned 1 exit status

Log: https://git.fh-aachen.de/vc9917e/ZSWatch/-/jobs/408382/raw

Have a look on the changes I made and see if I am missing something or if the MCUBOOT image should be somehow compiled with the net core.

https://git.fh-aachen.de/vc9917e/ZSWatch/-/compare/main...mcuboot?from_project_id=33311&straight=false

Disclaimer: I am using a private gitlab server (university) as its convenient for me to run CI/CD.

[jakkra]

You will probably not fit OTA with MCUBoot using internal flash, but you can try setting this to n it will make the image smaller:
https://github.com/jakkra/ZSWatch/blob/main/app/prj.conf#L180

[vChavezB]

I set the CONFIG_DEMO to n, and now it overflows to ~68 KB instead of ~362KB.

you will probably not fit OTA with MCUBoot

How would you suggest to add MCUBoot if it cannot fit in the internal flash?

[vChavezB]

I forgot that by default that the partition of the flash is managed by nordics partition manager tool. This in turn adds both mcuboot primary and secondary partition in the internal flash. I need to define the static partition file and it should resolve this problem I posted.

[vChavezB]

Now the image fits with the static partition.

Memory region         Used Size  Region Size  %age Used
           FLASH:      846840 B     998912 B     84.78%
             RAM:      185448 B       440 KB     41.16%
        IDT_LIST:          0 GB         2 KB      0.00%

[jakkra]

Ah nice, yeah that explains it :)

[vChavezB]

Just an update, I think the 5x6mm flash can be fitted. Just have to do some pcb gymnastics. Do you know why when I updated the pcb with the flash, C20 appeared in the PCB? (red circle).

[jakkra]

You can safely delete C20, it's in the schematic, but I routed it in a way I didn't need it to save some space, I think two IC share decoupling capacitor now.

[vChavezB]

Oh btw, do you have a part number that I could order for the display from mouser or digikey?

[jakkra]

Battery: https://m.aliexpress.us/item/2255799935668505.html?spm=

Screen: https://www.buydisplay.com/240x240-round-ips-tft-lcd-display-1-28-inch-capactive-touch-circle-screen
Note choose touch variant and with the pcb connector.

I do have spares of screen and battery plus the dock + dock connector, I could ship to you also if you are in a country it's easy for me to send to.

[jakkra]

Everything except screen and battery can be ordered from digikey, but unfortunately not those.

[vChavezB]

Hey thanks, that would make my life easier so I can just order from digikey. I would appreciate if you could send a spare screen and battery with the dock. I will send you a message over discord.

I think Im finished with the PCB. Hopefully I can order from JLCPCB and digikey this week and test the flash soon :)