February 2019 - Bluetooth-dev

Peripheral in .connecting state refuses to connect
by Rogers George 18 Feb '19

18 Feb '19

site_archiver(a)lists.apple.com Delivered-To: bluetooth-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=hidrate-me.20150623.gappssmtp.com; s=20150623; h=from:mime-version:subject:message-id:date:to; bh=2sKykaPIIY0kjL1lSvutkPFGgQen188UBzW7szA2c48=; b=xwu/j0vQn+mGCspRQo6PO1Ryl/Z5zOBde/DahcpDv00auit91a15/XZEqDlkBgB+vn I4uhNhIaKhFYYFLZMUdAuz5/E3wUR0x7AGXh+Aozq8r6CgeUY4PC7DqlLbfmN5pFPyZj 6A6fzW7F0YEtyU338HdyWpDn1y72FyMe5T2yzA806Iv5TCRvBttB5v9fnyZJWSN+FqrA YmLbAq+j/pjv54jUupWSDDHi/Yydf0bXTWJfrMmscylRAOJ+auoBn9JQSJ5yfB3nlEJO 9s8ZwTzPwPr8fihYyrfMH5tazgaCKMA1o8aHbVt9dlA6Vyuv8Ehl7hJRkWUY9abTcZCZ HD+A== Greetings. Once again there is a behavior we're seeing with our BLE devices that's got me stumped. We try to stay connected to our peripheral as long as it's in range. The Apple-endorsed strategy here is to call central.connect(peripheral) immediately on disconnection, and wait; and allow Core Bluetooth to reconnect and let us know on the appropriate delegate method. Turning on scanning is purportedly not necessary. Now, what we are actually seeing, is that occasionally we will have a CBPeripheral in the .connecting state, that refuses to connect even though our device is right next to the phone for multiple minutes. Our device has a fairly slow advertising interval, so our first thought was, oh, the phone just isn't seeing the ads, it'll get there eventually. But! I tried turning on scanning (we use [CBCentralManagerScanOptionAllowDuplicatesKey: true].) And lo and behold, the advertisements were coming through! We have clear cases where we have a CBPeripheral, in the .connecting state, and we are seeing advertisements from the device (via centralManager(central:didDiscover:...) that peripheral ), so it's clearly in range... but the connection just never opens. So I added a mitigation strategy: when trying to reconnect a peripheral, turn on scanning; then if n advertisements for that peripheral are seen within an x second window, call central.cancelPeripheralConnection(peripheral) (and then call central.connect(peripheral) on the next advertisement.) This might be a little battery-demanding, but seems to work; so we left it at that for about a year. (current values for n and x are 6 and 60.) More recently, I started logging this occurrence to os_log and to Crashlytics, to see how widespread a problem this is, and in hopes that it was fixed in ios 11 or 12. Over 20% of our customers are running into this! Ideas? How could this state be reachable? Could my mitigation strategy be making things worse somehow? Worse, we've recently been getting some customer reports that our peripheral is not always connecting, and occasionally see this ourselves (not when running attached to Xcode, of course.) When it happens in-house, briefly turning on Airplane Mode to power down the bluetooth radio always fixes the problem. I don't know enough yet to say that this is related but I have a bad feeling. (Apple engineers, if you want to peek at this I think you have some of our device in hand ( hidratespark.com <http://hidratespark.com/> ), but let me know if you would like some more.) -- R. _______________________________________________ Do not post admin requests to the list. They will be ignored. Bluetooth-dev mailing list (Bluetooth-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/bluetooth-dev/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Re: 📡 Synchronization of timestamps, using Bluetooth Connection Event?
by Matthias Ringwald 13 Feb '19

13 Feb '19

site_archiver(a)lists.apple.com Delivered-To: Bluetooth-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=bluekitchen-gmbh.com; s=default; h=To:References:Message-Id: Content-Transfer-Encoding:Cc:Date:In-Reply-To:From:Subject:Mime-Version: Content-Type:Sender:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=eFeRbf+DAvcUo17sY9mkpuzJxQCBo529Wp/0Oftce0Q=; b=MVfoAl1I2Bo4rJXVODe0S1rUq s+Ab4NMPqymLCzRYFvLR8JjexdM5ZGAZZV4sBQ4D3aLQFlh+hE5sKSmNjESuXtsO83xsgvnEpAUkk Om2Ch5koa0Vc23r4O65teB6WFAfEvPp6msjmZikcclQZAxq/ZxadVdAhSgGHrNHzcjh0MPgFOeUiV sjPdepUb7F6682iF5K+yqdriC9DyHV9XrnIkc+ira4BhoaMHgppCCjwUTKKJtkr5r067s2y7xwoBz A0cTPb4h9B9MNLhzUOV/6M+ok0zD9euduv1o3oeS5ac1LvCMFpK413I4KQy1K3boyilnIC4eyLapo uE+ehi8xA==; Hi Julian Under the assumption that you don't have much control over the iOS side, I would try to minimize unknown latencies there. If you're sending, you cannot know when the Connection Event happens, so you have the time until next CE plus the time through the iOS stack. Because of this, I'd suggest to send a timestamp from the nRF52 to iOS. Then, you only have the time it takes from the Bluetooth Controller through the stack to the app. I would hope that this might be possible in 1-2 ms if your app in front. Now, for the nRF52, there you're aware of the Connection Event and queue a packet e.g. 2 ms before the next CE and put that time into the timestamp. On iOS, the might be a random jitter. However, knowing the connection interval, you can always identify the timestamp with the shortest delay through the stack. If you're take this idea for a spin, I'd be curious to learn if that worked, and how well.. Cheers Matthias — Dr. sc. Matthias Ringwald CTO and Co-founder of BlueKitchen GmbH, Zurich https://bluekitchen-gmbh.com > On 12 Feb 2019, at 12:25, Julian Vogels <julian(a)soundbrenner.com> wrote: > > Dear list, > > Thank you for interesting topics and your support in the past. > > We’re building a peripheral device (Nordic nRF52840) which needs to be time > synchronized with the central device (iOS device) once on connection. > When sending a timestamp, we have unknown, noticeable latency. This is > because we cannot know the time it takes until one packet is processed on the > central side, sent, and then received and processed on the peripheral side. > However, we do know that there are Connection Events (CEs) occurring every > Connection Interval (30 ms), where the packets are exchanged. We were > planning on using the CEs to infer the actual time of send/receive, as the > event is happening at the same time on both sides and has a very short > duration. > > On the peripheral device, we are able to generate an interrupt when the CE > occurs. On the iOS device, we are unable to detect when a Connection Event is > occurring. > Is there any way to get the synchronized Bluetooth clock tick (Connection > Event) on iOS? Or maybe we’re on the wrong track altogether? > > Any other ideas on how do you synchronize two timestamps on peripheral and > central device? (We already have clock drift compensation by the way, I am > just asking about timestamp sync.) > Our requirement is a latency/jitter under 5-8 ms. > > I hope I sparked someones interest in this engineering problem! Please send > me a message if anything is unclear. > > All the best, > > Julian > Julian Vogels > CTO & Co-Founder > +49 176 5659 1152 (GER) | Skype: julian.vogels | WeChat: julianvogels > www.soundbrenner.com > > > Download our free standalone app "The Metronome by Soundbrenner" for iOS or > for Android > > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Bluetooth-dev mailing list (Bluetooth-dev(a)lists.apple.com) > Help/Unsubscribe/Update your Subscription: > https://lists.apple.com/mailman/options/bluetooth-dev/matthias%40bluekitche… > > This email sent to matthias(a)bluekitchen-gmbh.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Bluetooth-dev mailing list (Bluetooth-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/bluetooth-dev/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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Re: 📡 Synchronization of timestamps, using Bluetooth Connection Event?
by Spero Koulouras 13 Feb '19

13 Feb '19

site_archiver(a)lists.apple.com Delivered-To: Bluetooth-dev(a)lists.apple.com Julian - Have you read this paper: https://www.eit.lth.se/sprapport.php?uid=945 It is pretty on-point for what you are trying to achieve. On Tue, Feb 12, 2019 at 3:26 AM Julian Vogels <julian(a)soundbrenner.com> wrote: > Dear list, > > Thank you for interesting topics and your support in the past. > > We’re building a peripheral device (Nordic nRF52840) which needs to be *time > synchronized* with the central device (iOS device) once on connection. > When sending a timestamp, we have unknown, noticeable latency. This is > because we cannot know the time it takes until one packet is processed on > the central side, sent, and then received and processed on the peripheral > side. However, we do know that there are Connection Events (CEs) occurring > every Connection Interval (30 ms), where the packets are exchanged. We were > planning on using the CEs to infer the actual time of send/receive, as the > event is happening at the same time on both sides and has a very short > duration. > > On the peripheral device, we are able to generate an interrupt when the CE > occurs. *On the iOS device, we are unable to detect when a Connection > Event is occurring*. > Is there any way to get the synchronized Bluetooth clock tick (Connection > Event) on iOS? Or maybe we’re on the wrong track altogether? > > Any other ideas on how do you synchronize two timestamps on peripheral and > central device? (We already have clock drift compensation by the way, I am > just asking about timestamp sync.) > Our requirement is a latency/jitter under 5-8 ms. > > I hope I sparked someones interest in this engineering problem! Please > send me a message if anything is unclear. > > All the best, > > Julian > <http://www.soundbrenner.com> *Julian Vogels* > CTO & Co-Founder > +49 176 5659 1152 (GER) | Skype: julian.vogels | WeChat: julianvogels > www.soundbrenner.com > [image: LinkedIn] <https://www.linkedin.com/company/6396866> [image: > Indiegogo] <http://bit.ly/soundbrennerpulse> [image: Facebook] > <https://www.facebook.com/soundbrenner> [image: Twitter] > <https://www.twitter.com/soundbrenner> [image: Instagram] > <https://www.instagram.com/soundbrenner> > Download our free standalone app "The Metronome by Soundbrenner" for iOS > <https://goo.gl/BivAYK> or for Android <https://goo.gl/Ejruwi> > > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Bluetooth-dev mailing list (Bluetooth-dev(a)lists.apple.com) > Help/Unsubscribe/Update your Subscription: > https://lists.apple.com/mailman/options/bluetooth-dev/spero%40koulouras.com > > This email sent to spero(a)koulouras.com > _______________________________________________ Do not post admin requests to the list. They will be ignored. Bluetooth-dev mailing list (Bluetooth-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/bluetooth-dev/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com

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📡 Synchronization of timestamps, using Bluetooth Connection Event?
by Julian Vogels 12 Feb '19

12 Feb '19

site_archiver(a)lists.apple.com Delivered-To: Bluetooth-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=soundbrenner-com.20150623.gappssmtp.com; s=20150623; h=from:mime-version:subject:message-id:date:to; bh=pgFD8O4qgdJ+YqVYt2ykfVVFoJDaZk96RCSuASjn1QQ=; b=WKrOuxAleNM9nmddkCPDnH/WUkUF5mWld9/pMx6Yi2s9IjujX27IqK2Y9V9NA6LyuT jCSwrqRIVwsgXtHSVswDm54b4HmG6P/c3aGj8qA90ttj88AizUf7LnQHXfqBigJH5Lft N+TMVA0ahuS6RUWb+ZS2ClzluKnGQVdFRh2zS1f084GlNuWcrmEVjUc6Ttvtb8fDvfLi OeG8rXblfeKZn1+x+RCgPaqpz06uad8hSNrZvDWzTYUNlehRTvKQ0XuBXh8WWnqU6dKI GgQBRVhY0FwPMxznYd13q5n5LOSPwdTkt7IYw/I20bJG8bn9o5UwQSLZ55ezj8C4IaoV 2ClA== Dear list, Thank you for interesting topics and your support in the past. We’re building a peripheral device (Nordic nRF52840) which needs to be time synchronized with the central device (iOS device) once on connection. When sending a timestamp, we have unknown, noticeable latency. This is because we cannot know the time it takes until one packet is processed on the central side, sent, and then received and processed on the peripheral side. However, we do know that there are Connection Events (CEs) occurring every Connection Interval (30 ms), where the packets are exchanged. We were planning on using the CEs to infer the actual time of send/receive, as the event is happening at the same time on both sides and has a very short duration. On the peripheral device, we are able to generate an interrupt when the CE occurs. On the iOS device, we are unable to detect when a Connection Event is occurring. Is there any way to get the synchronized Bluetooth clock tick (Connection Event) on iOS? Or maybe we’re on the wrong track altogether? Any other ideas on how do you synchronize two timestamps on peripheral and central device? (We already have clock drift compensation by the way, I am just asking about timestamp sync.) Our requirement is a latency/jitter under 5-8 ms. I hope I sparked someones interest in this engineering problem! Please send me a message if anything is unclear. All the best, Julian <http://www.soundbrenner.com/> Julian Vogels CTO & Co-Founder +49 176 5659 1152 (GER) | Skype: julian.vogels | WeChat: julianvogels www.soundbrenner.com <http://www.soundbrenner.com/> <https://www.linkedin.com/company/6396866> <http://bit.ly/soundbrennerpulse> <https://www.facebook.com/soundbrenner> <https://www.twitter.com/soundbrenner> <https://www.instagram.com/soundbrenner> Download our free standalone app "The Metronome by Soundbrenner" for iOS <https://goo.gl/BivAYK> or for Android <https://goo.gl/Ejruwi> _______________________________________________ Do not post admin requests to the list. They will be ignored. Bluetooth-dev mailing list (Bluetooth-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/bluetooth-dev/site_archiver%40lists… This email sent to site_archiver(a)lists.apple.com signature.asc

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