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DFU on nRF51822 + iOS -- Have to toggle Bluetooth ON/OFF

Tim Clark

I'm wondering (hoping) if there is something that I'm not doing correctly ...

We have a BLE application on the nRF51822 which has been working nicely. It is a custom BLE Service/Characteristic which supports a command/response protocol that we've developed for reading the captured information on our device.

We also support DFU mode -- using the DFU bootloader example -- pretty much AS-IS, except for checking the (gpregret == 1) condition on reset (which we set in the main application via a BLE command).

What 'appears' to be happening is this :

1 -- BLE application is running, connected to the iOS App -- able to view data, etc.

2 -- DFU 'key' is hit in the App which does the following on the device : sd_power_gpregret_set(0x01); sd_nvic_SystemReset();

3 -- The device resets, detects the gpreget bit set -- and (successfully) enters DFU mode.

4 -- We use nRF Toolbox to update the F/W. All works well -- find DfuTarg, select file, file type, etc. Upload is successful. Device resets and is now running with new F/W.

5 -- Here is where it gets 'weird' ? In order to get the device to show-up again (even if I remove power from the device and then bring it back up) -- I must cycle BT Off/On on my iOS device! Our App is looking for it's desired Service UUID (0x1723) and Characteristic (0x1724) -- and doesn't find them.

6 -- Prior to cycling BT Off/On in the Settings Menu -- if I run an App that I downloaded on iTunes : itunes.apple.com/.../id525235616 -- then what I see are the Service/Characteristics (0x1530, 1531, 1523) which are the ones in the DFU Bootloader?!?!

SO -- it seems like somehow/someway? iOS is 'latching' those DFU characteristics -- even though the device is correctly advertising with it's non-DFU (1723/1724) Service/Characteristic.

As soon as I cycle BT Off/On on the iOS device -- even the BLE Tool shows the proper results (0x1723/1724) -- with the device being on throughout all this -- no change to/from DFU mode.

I'm wondering if it there is any chance that iOS is getting irk'd with the fact that the default DFU bootloader calls the device DfuTarg -- and our application code calls it something different?

Appreciate any input/guidance that you might have -- as it just can't be that we have to tell user's to cycle BT after a F/W update!

Cheers, -Tim

  • 0

    I had a similar issue where my iOS app wasn't properly handling a reconnect from the peripheral, so I had to also either toggle bluetooth on/off or reset the app. Did you confirm that your CBPeripheral object is set to nil upon a disconnect, if your CBPeripheral has a singleton/shared instance delegate, it's being managed properly, and that you re-enable scanning? Those 3 things contributed to me seeing that behavior, but all the root cause was on the iOS side.

  • 0 in reply to jt

    Thanks for the suggestions!

    I haven't checked the source code for nRF Toolbox (just downloaded from the App store) -- but it seems like our App must? be closing-out OK if nRF Toolbox is successfully discovering the DFU Service/Characteristic -- but then after nRF Toolbox is done -- I'm not able to see my device post-DFU.

    Guess would be great to hear is if anybody has had issues using the nRF Toolbox DFU -- then their device not showing up afterwards?

  • 0

    Tim,

    This is probably the same bug I encountered awhile back while trying to get a DFU bootloader to work with iOS apps. My firmware used to work back on iOS 7, but broke when the phone was upgraded to iOS 8. What I eventually discovered is that in iOS 8, for some reason the Bluetooth stack will now save the advertising data of any Bluetooth smart device it connects to somewhere in memory at the moment of connection. The old advertising data will then be recalled and used the next time the peripheral advertises to the phone instead of the current advertising data. Therefore, except for first time connection the phone app will always be "one connection behind" in terms of what it reports is contained in the advertising data. Because I used the advertising data to tell the app when to use the bootloader as well, it got confused and couldn't connect up properly.

    For now I'd avoid using the advertising data as a means to determine if your device wants to run normally or enter bootloader mode. If it's possible to do and your phone app is flexible enough, I'd recommend altering your bootloader advertising data to exactly match the firmware main data, and have your phone app always search for the common data. On connection, perform a service discovery and use the services the peripheral reports are available to determine what mode the device is in, and handle it appropriately from there. Alternatively, create a custom common service between the bootloader and main firmware app whose sole purpose in life is to send a one byte value to the phone to tell it whether the device is in bootloader or main code.

    Nate

  • 0

    Yes, there is something you're not doing correctly. You need to:

    (1) Read the Bluetooth Spec. (2) Read Apple's Bluetooth Accessory Design Guidelines (maybe start here as it's only a few pages long and has the answer plainly written in it).

    Both the reason why you are seeing this behaviour and the way to 'fix it' is included within these documents.

    Contrary to the [incorrect] comments above, Apple's iOS behaviour is not erroneous and is 100% per the Bluetooth Spec. Nor was this suddenly introduced in iOS8. Apple are pretty serious about BLE and don't tend to cut corners, despite CoreBluetooth not being the most friendly API around ;)

    -m

  • 0

    Hi Tim,

    I agree with Nate and jt, this does indeed look like a caching issue.

    One problem with the bootloader as it is now is that the bootloader has a completely different GATT database than your normal application. When a Central device re-connects to your nRF51, it expects that the GATT database is the same, so it can avoid doing a Service Discovery procedure (which takes time). Bluetooth does have functionality for dealing with this situation: one of the native characteristics on a BLE device is the "Service Changed Characteristic". The idea is that the GATT Server can use this to indicate to the GATT Client that the GATT database has changed (see developer.nordicsemi.com/.../a01060.html. There's not guarantee that the peer device will take action when this happens, but it's worth a try looking into. Note that with S110 v7.0.0 and later, you must specifically tell the stack to include this characteristic when enabling the stack (see developer.nordicsemi.com/.../a01045.html

    You can also add the DFU Service to your normal GATT database before your other services. I mean, just add the Service to your database, but not include any of the actual bootloader functionality in there. This way the peer device will the the following services during normal operation:

    • DFU Service
    • Battery Service (for example)
    • Device Information Service (for example)
    • Your other Services

    When the bootloader is active, the peer device will see the following services:

    • DFU Service

    Thus you won't have to force flushing the cache in order to find the DFU Service in bootloader mode (as the DFU Service will now be at the exact same place in the GATT database), and hopefully you will see the full set of Services again when you resume normal operation.

    It might be easier to "just" flush the cache when triggering the bootloader, but I'm not exactly sure how/if that can be done without disabling and re-enabling Bluetooth (I'm not an iOS developer).

    Hope this helps!

    Audun

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