I tried this, but sadly it doesn't work.
I haven't investigated why it doesn't work though.

No worries, my nrf52840 just showed up so I'll investigate

@mikesmitty any update on this? I would really like to have it for something... 😸

Oh yeah, this fell off my radar. I've got a debugger just about set up with an nrf52840 now so I can dig into this again

Ok, at least in my testing it looks like it's just a problem with m.buf being too small. My test device has a write block size of 4 bytes, which I didn't think would ever happen. The m.buf buffer is set, perhaps a bit naively, to use the write block size as a capacity, but it needs to be 64 bytes at a minimum to be able to store a full usb packet and it's panicking.#5017 also modifies these buffer sizes but in a more expansive way so this will likely end up just being a temporary patch. I just saw Ayke commented again on that one so I'll swap back to that one next

Pinging Dr.@mikesmitty 😸

Sorry, been getting distracted a lot recently haha. I'll start working on this again this weekend

Thank you!

I gave it a try today on XIAO BLE board.

"usb-storage" example compiles and flashes to the board.

Mac can see the device, but can't really use it. I've tried to "Erase" it with Disk Utility, that just hangs.

See screenshots.

Same happens withxiao-rp2040 target though, which as I understood is supposed to work, so either nrf version already works as expected OR we need a better example to try with OR need an instruction how to initialize the storage device.

Ok, finally getting back into this now. Let me see where I left off

Just in case it helps in any way, here is UF2 bootloader for nRF52 chips.
Boards with UF2 bootloader show up as mass storage devices.

https://github.com/adafruit/Adafruit_nRF52_Bootloader/blob/master/src/usb/usb.c

Woof, that was an adventure. The usb endpoint handling logic for nrf52840 was unconditionally accepting packets and I ended up having to rework it a little bit in order to allow returning a NAK when needed, but it seems to be working for me now if you guys want to give it a shot

@ysoldak please give this PR another try if you get a chance.

Still can't see Mass Storage Device when flashing usb-storage example to XIAO BLE board.
tinygo flash -target=xiao-ble -opt=z ./src/examples/usb-storage

There is no popup with Eject, Ignore and Initialize... buttons anymore, but nothing else either.

Is there any other (better) way to test?

Sorry, I've been playing whackamole with bugs in this one a little bit. I started putting together a branch with tests to try and iron those out properly. I'll trim this back and put those in the other branch

@mikesmitty#5109 has been merged, perhaps this PR can now be rebased and retested?

I rebased if you want to give it a go, but I haven't tested it yet. I spent a bunch of time arguing with both the jlink and the nrf52 board, but I've finally got a reliable workflow going again

Ok, nailed down the bug I was stuck on for the longest time where endpoint stalls were hanging indefinitely and the CSW was not being returned. In order to reset the DATA0/DATA1 insetEPDataPID like is done after an endpoint stall you have to actually write the register twice. Once with just the endpoint address, then again with the address combined the new DATA0/DATA1 value at the appropriate offsets. Getting a new hang now, but making progress

Alrighty, I fixed the last bug I was running into and pushed the changes up on#5110 since that's where I was doing my testing. I tried porting the change back over to this branch, but it's running into some fatal bug on this branch and I don't have time to sort it out this morning. I'll sort out/split up the changes a bit later, but for now you can try out the changes on that other PR

Edit: Oh, actually there's another new bug, but it enumerates properly now. I'll take a look into it a bit later

Alrighty, I fixed the last bug I was running into and pushed the changes up on#5110 since that's where I was doing my testing. I tried porting the change back over to this branch, but it's running into some fatal bug on this branch and I don't have time to sort it out this morning. I'll sort out/split up the changes a bit later, but for now you can try out the changes on that other PR

Edit: Oh, actually there's another new bug, but it enumerates properly now. I'll take a look into it a bit later

Thanks for working on this@mikesmitty ❤️