[Bug] Unable to use NFCT

[nitz]

Describe the bug When using the UF2 bootloader, I'm unable to use the NFCT peripheral, despite the API calls looking okay.

Set up (please complete the following information)

• Using the nRF52840 M.2 Dev Kit from makerdiary. For the board configuration, I'm basically using their fork's version here but updated to have a pinconfig.c like the other boards. I've attached my current copy here boards-nrf52840_m2.zip. (Note the -U CFLAG in the mk, more on that in a bit.)
• Win10 Pro/Workstations 20H2 (19042.388)
• Not much serial log to show, as everything is pretty much generated from my output, but here's what it looks like anyways, once the application is running:

  <debug> app: =====================================
  <info> app: Application starting.
  <debug> nfctagemu: Initializing Type 2 Tag NFCT via nrfx. (0x047D)
  <info> NFCT: Initialized
  <debug> nfctagemu: Payload set @0x200000EC
  <info> nfctagemu: Tag enabled.
  <info> NFCT: Start
  <debug> app: Application waiting for events!
  (the NFCT events never come...)

To Reproduce Steps to reproduce the behavior:

1. Set up a board that you plan to use the NFCT on
2. Comment out the CFLAGS += -DCONFIG_NFCT_PINS_AS_GPIOS line from the main Makefile, so the system init doesn't try to skip the NFCT antenna pins. (I tried using CFLAGS += -UCONFIG_NFCT_PINS_AS_GPIOS in the board.mk file, but since it's evaluated before the line that adds the define, it never ends up being useful. Maybe we could move the CFLAGS defs above the included *.mk files?)
3. Flash the bootloader.
4. Use the bootloader to install an application with which to use the NFCT, using a phone reader software or other, observe it not working.
5. Using a non UF2 flash/bootloader, flash that same application. It works!

Expected behavior I should be able to use the NFCT. I might just be missing something that I've not got set up.

Screenshots N/A

Additional context I went back through the commits to see why the -DCONFIG_NFCT_PINS_AS_GPIOS was added, and that definitely made sense. I do feel though that boards should be able to opt in to using the NFCT pins as NFCT pins via something in their board.h/board.mk Though it's clear that the define isn't my only problem :)

[hathach]

I don't think we could help with this. Maybe someone that works more with NFC could, label as help wanted

[nitz]

Sounds good! I plan to keep digging at it, as I'm sure it's almost gotta be just a register configured incorrectly or something. Will update with progress as I make any!

[hathach]

NFC pin usage must be configured with UCIR, maybe the bootloader doesn't enable it by default. I kind of forgot, here is way to do it in application. https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/master/libraries/Bluefruit52Lib/examples/Hardware/nfc_to_gpio/nfc_to_gpio.ino

If it is the case, we could definitely do it within board.h with an macro.

[nitz]

Yeah, that's what the CONFIG_NFCT_PINS_AS_GPIOS seems to toggle, in system_nrf52840.c in NFRX.

    #if defined (CONFIG_NFCT_PINS_AS_GPIOS)
    #error If you can read this, you definitely don't have NFCT

        if ((NRF_UICR->NFCPINS & UICR_NFCPINS_PROTECT_Msk) == (UICR_NFCPINS_PROTECT_NFC << UICR_NFCPINS_PROTECT_Pos)){
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_UICR->NFCPINS &= ~UICR_NFCPINS_PROTECT_Msk;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NVIC_SystemReset();
        }   #endif

I stuck a #error in there to make sure the define was getting properly dropped when I commented it out of the Makefile, but I only just now stopped to wonder if SystemInit() is called by the bootloader. I guess I assumed it was, seemed "startuppy", but I haven't looked at it at all yet.

[hathach]

could you tell us whether you figured out way to fix this ?

[nitz]

Hey! I actually had stuck this on the backburner while I was focusing on my app, and was just using the default nRF5 MBR with no bootloader for now. But I've reached a "MVP" for my app, and am waiting on a PCB spin, so I will take a look at this today!

[nitz]

Alrighty then! It looks like I got it working!

A comment in the .ino you linked actually may have uncovered what part of the issue was I was facing. It seems that once you write those UICR bits, unless you flash with a method that is going to re-flash them, they won't clear. (Despite my attempts to do so in software.) I think the major part of what happened was I had first flashed the bootloader with the "fresh out of the repo" build, which builds with CONFIG_NFCT_PINS_AS_GPIOS and SOFTDEVICE_PRESENT defined.

With CONFIG_NFCT_PINS_AS_GPIOS, in system_nrf52840.c as I pointed out above, it does in fact set those bits. So even though I flashed over the bootloader with my builds later that took those defines out, it took a full chip erase and then re-flash of the bootloader without those defines present. So at the very least, it'll need to be optional for that flag to be defined (or rather, undefined?) by the board.mk

I just created a PR for the board I'm on currently (#155), and figure we can discuss on there how to best handle those symbol undefs!

[nitz]

Closing this as #155 solved it!