Nus profile seems to cause system reset if the data length too long.

[Ted]

iphone5_b.psdm370_android6_b.psdlong_write_error.pngI using SDK11. I porting nus profile to my system and make a customer's UUID. I use Lightblue on iPhone 5 to connect my system. I sent a data through my customer's UUID. My system work fine when the data length is less than or equal 20 bytes. It will cause system reset if the data length is great than 20 bytes. Was the softdevice error, or I made something wrong?

[Petter Myhre]

The system is probably reset because APP_ERROR_CHECK() is called with something else than NRF_SUCCESS (0x00000000) somewhere. If you call ble_nus_string_send() with a longer length than 20 bytes it will return NRF_ERROR_INVALID_PARAM.

The maximum ATT MTU with the S130 v2 is 23 bytes, the header is 3 bytes, so up to 20 bytes of data is allowed.

[Petter Myhre]

Ok. So you get into trouble when you are trying to write more than 20 bytes into the TX characteristic. Firstly, as I mentioned above, the maximum ATT MTU with the S130 v2 is 23 bytes, the header is 3 bytes, so up to 20 bytes of data is allowed in one operation. So you are probably triggering long write/queued write by trying to write more than 20 bytes, which is not supported by nus, see this for more information. Secondly, the maximum length of the TX characteristic value is 20 bytes, so if you want to actually do a long write you have to change this. But in most cases it is better to split your data into 20 byte pieces and reassemble the data in the peer application.