Write to variable length characteristic

RE: Write to variable length characteristic

Ulrich Myhre — Fri, 06 Jun 2014 09:40:04 GMT

If you don't need to write everything at once (i.e. data is not always consistent during writes), you can write with offsets. The way to do this is to run sd_ble_tx_buffer_count_get() to get the maximum number of buffers. Split the data into N 20-byte chunks, then for i=0 to N-1 queue them with gattc_write(data[i*20], len=min(20,total_len-20*i),offset=i*20), decrementing your buffer count manually. If you run out of buffers or receive a BUSY return code, wait/sleep until you receive more BLE_EVT_TX_COMPLETE events, and increment your buffer count by the count in the event.

If you lose your connection, you can only assume that [Total count of TX_COMPLETE counts] packets were sent, and you should continue writing from that place upon reconnection.

RE: Write to variable length characteristic

Ulrich Myhre — Fri, 06 Jun 2014 09:33:07 GMT

Long writes can be used to write everything in a single go, even across multiple characteristics, but it is not required to write to longer attributes. If it is acceptable that the data is half-written at any point, writing with an offset is perfectly possible.

RE: Write to variable length characteristic

Naveen — Thu, 05 Jun 2014 11:39:52 GMT

I will come back on this example. As it is not working properly with Master Control Panel, I will check with iphone.

RE: Write to variable length characteristic

Naveen — Thu, 05 Jun 2014 11:38:31 GMT

nRF51822 with the S110 is peripheral and iphone is central characteristic in the GATT Server at the peripheral (nRF51822 with the S110) and iphone as client. I want to send data more than 20 bytes from GATT server and vice versa.

RE: Write to variable length characteristic

FormerMember — Thu, 05 Jun 2014 08:01:50 GMT

If you want to transfer more than 20 bytes from the GATT Client to GATT Server, GATT Long write has to be used, see this post.

If you want to transfer more than 20 bytes from GATT Server to GATT Client, read blob or notification can be used.

RE: Write to variable length characteristic

Petter Myhre — Thu, 05 Jun 2014 07:11:21 GMT

What peripheral and central device are you using? nRF51822 with the S110? Is the characteristic in the GATT Server at the peripheral or central device? devzone.nordicsemi.com/.../