Apple

On May 23, 2013, at 6:10 AM, Sébastien Martini <email@hidden> wrote:

On this same topic, I was doing more tests and and I have a new question, maybe someone can help me:

I was trying to read (still using method readValueForCharacteristic) a long dynamic value of a characteristic (by long I mean > 8ko) and the problem is I'm only able to read the first 528bytes of this characteristic. I was wondering: am I doing something wrong as I should be able to read all the data? or is there a limit on the size a long read can be?

Thanks for your help.

On Fri, Apr 12, 2013 at 1:57 PM, Etan Kissling <email@hidden> wrote:

For initiating data transfer form the peripheral, only notifications / indications are supported.
There does not currently exist something like a Long Indication or Notification.

Etan

On 12.04.2013, at 13:55, Sébastien Martini <email@hidden>

wrote:

Great, thanks.

I guess, I've got a bit lost after reading the sample code "BTLE_Tranfer" where notifications are explicitly sent by chunks. It's not super easy to see at first what the CB framework does implement of the specifications and how much the CB framework assists you.

On Fri, Apr 12, 2013 at 1:39 PM, Etan Kissling <email@hidden> wrote:

Sébastien,

Yep, that's true. You can read about the exact underlying process in
Bluetooth Core Spec V4.0 Volume 3 Part G Section 4.9.4 and 4.8.3.
(https://www.bluetooth.org/en-us/specification/adopted-specifications)

Etan

On 12.04.2013, at 13:33, Sébastien Martini <email@hidden>

wrote:

Ok, thank you Etan I see now.

I've just tested with a long read characteristic value request and indeed it asks for increasing offset values on my peripheral manager delegate method, here is my code:

- (void)peripheralManager:(CBPeripheralManager *)peripheral didReceiveReadRequest:(CBATTRequest *)request {
NSData *value = ... // my long value

NSRange chunkRange = NSMakeRange(request.offset, [value length] - request.offset);
request.value = [value subdataWithRange:chunkRange];

[self.peripheralManager respondToRequest:request
withResult:CBATTErrorSuccess];
}

So what happens if I understand correctly is that when I emit a -readValueForCharacteristic: on my central, it internally asks the peripheral to send him the data by issuing requests with increasing offset values and will detect there is no more data to read when a returned chunk is 0 or less than the size of the MTU. Is this correct?

Thanks for your help!

On Fri, Apr 12, 2013 at 1:00 PM, Etan Kissling <email@hidden> wrote:

Sébastien,

BLE allows to send bigger data packets than 20 bytes (Write Long Characteristic Value /
Read Long Characteristic Value). In these cases, the data is split to smaller chunks in which
the offset value may be used in iOS. Note that you cannot increase throughput by using these
values, though.

If you don't use Write / Read Long Characteristic Value procedures, offset should always be 0.

Etan

On 12.04.2013, at 12:51, Sébastien Martini <email@hidden>

wrote:

> Hi list,
>
> Is there a case in practical where this attribute can have a value different than 0 ?
>
> Given it seems it is already our responsibility to send data by 20 bytes chunks, I don't see where this offset could be different than 0, especially given it is a read-only attribute for us.
>
>

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References:
	>Re: Question about CBATTRequest.offset (From: Sébastien Martini <email@hidden>)
	>Re: Question about CBATTRequest.offset (From: Jason Conn <email@hidden>)