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Re: Data loss during BTLE repeated write with CoreBluetooth on iOS
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Re: Data loss during BTLE repeated write with CoreBluetooth on iOS

  • Subject: Re: Data loss during BTLE repeated write with CoreBluetooth on iOS
  • From: "Tom \"Tyris\" Graham" <email@hidden>
  • Date: Tue, 29 Apr 2014 09:57:31 +1000
Hi Nick,
We use BLE to copy files and firmware updates to our peripheral, so we've struggled with getting the throughput up.
One of the very early problems we had was with the peripheral having no fifo on its receive buffer (I think it was the TI CC2540). This was causing it to drop data due to the buffer wrapping if we sent it too quickly.
We're now using a different chip (dual BLE and classic) that doesn't have this problem. From the iOS end we can call writeValue with WriteWithResponse as fast as we need to and we no longer get any data loss.

Regards,
Tom 


On 29 April 2014 08:43, Nick Brook <email@hidden> wrote:
After some testing of the suggested 4 writes every 50ms, I can only get it to transfer all data if I do 1 write every 100ms.  Any less than that and packets are dropped.  This is on an iPad Mini with retina display, iOS 7.1.1, Bluegiga BLE113.  100kb therefore takes over 8 minutes.  Perhaps it is something to do with the time taken to handle the data on the peripheral, in my case write to flash.

Nick


On 26 Apr 2014, at 20:14, Nick Brook <email@hidden> wrote:


On 24 Apr 2014, at 15:50, email@hidden wrote:

* Use write without response as it's much faster than waiting for a
response on every block of data sent
* send four blocks, then sleep for a tenth of a second, and repeat until
all data is sent.
* send the block index with your data so your BTLE device can determine if
it receives any blocks out of order
* have your iOS app subscribe to notifications on a "restart sending at
block N" characteristic
* if BTLE device receives any block out of order have it notify "restart
sending at block N" which your iOS app is listening to, this will allow you
to have the iOS side backup to the index requested by the BTLE device.

I thought packet order was guaranteed by the Bluetooth stack, from https://en.wikipedia.org/wiki/Bluetooth_protocols#Logical_link_control_and_adaptation_protocol_.28L2CAP.29

"In-order sequencing is guaranteed by the lower layer.”

So if packets are out of order, surely that’s a bug with CoreBluetooth?

Does it specify somewhere in the docs that you should only perform 4 write operations every 30ms?  Surely this should be handled more gracefully by the framework, for example like peripheralManagerIsReadyToUpdateSubscribers: on CBPeripheralManager:

When a call to the updateValue:forCharacteristic:onSubscribedCentrals: method fails because the underlying queue used to transmit the updated characteristic value is full, theperipheralManagerIsReadyToUpdateSubscribers: method is invoked when more space in the transmit queue becomes available. You can then implement this delegate method to resend the value.


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 >Re: Data loss during BTLE repeated write with CoreBluetooth on iOS (From: Nick Brook <email@hidden>)
 >Re: Data loss during BTLE repeated write with CoreBluetooth on iOS (From: Nick Brook <email@hidden>)

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