Queued Writes characteristic value longer than 220B

[Piko]

Hello.

I neet to write long characteristic value (250B). I use GATTS Queued Writes from example devzone.nordicsemi.com/.../ based on developer.nordicsemi.com/.../a00892.html I send data from nRF Master Control Panel (Android 4.4, Nexus 4) and watch on-air communication witch sniffer, code is written for nRF51822 XAA, SoftDevice S110 version 7.1.

I is almost work: when I send up to 220 bytes value I see on snifer sequence of Prepare Write Request and Prepare Write Respons with consecutive offests, and at the end there is Execute Write Request, and characteristic is written. BUT, when I want send longer value (eg 221 bytes long) after sequence of Prepare Write Request/Response there is Prepare Queue Full and write is canceled.

How long is this queue in Queued Write? Is this configurable? Is there a different method to write characteristic value longer than 220B.

[Pål Håland]

Hi

Piko, the best way to determine how much space you should provide when you receive BLE_EVT_USER_MEM_REQUEST is the following calculation.

H = handle (2 byte) + offset (2 byte) + length (2 byte) = 6
MTU = 23
DATA = MTU-H = 17

Total Memory = ceil(Char Max Len*MTU/DATA) + 2

[Piko]

Hello Thanks for answer. But my problem isn't space provided by me. When I receive BLE_EVT_USER_MEM_REQUEST I allocate by sd_ble_user_mem_reply memory block equals to characteristic value = 250B. I even try allocate more = 300. But, with that you write, this means that I need more memory than characteristic value lenght. Is this right? Where I can read about that? thanks Piko

[Pål Håland]

If you have a 250 byte long characteristic value it would be: ceil(250*23/17)+2 = 341 byte

Not sure if it is documented anywhere, the structure used for reading back the part values can be located here: developer.nordicsemi.com/.../a01075.html