Increase characteristic value max length

Question

Sorry ,I have the problem with increasing the max data length(more then 20 bytes) in the characteristic , I change the att_mtu size like the value in the picture, but after I changed it, I can't even detect my device name , is there any else I have to do when I change the size? I'm using sdk 15.3 ,template project.

bjorn-spockeli · Answer

Im not sure if you will be able to get out two packets if sd_ble_gatts_hvx is called every 3ms. It could be that the SD will end the connection event if there are no data in the queue. So if you update the data and call sd_ble_gatts_hvx right before the start of the connection event and then call sd_ble_gatts_hvx again after 3ms, then the connection event may already be closed. However then you should be see two packets going out on the next connection event if sd_ble_gatts_hvx was called twice before the start of the event. If you are getting NRF_ERROR_RESOURCES when calling sd_ble_gatts_hvx then please see the API doc, quoted below. 
 The number of Handle Value Notifications that can be queued is configured by ble_gatts_conn_cfg_t::hvn_tx_queue_size When the queue is full, the function call will return NRF_ERROR_RESOURCES . A BLE_GATTS_EVT_HVN_TX_COMPLETE event will be issued as soon as the transmission of the notification is complete.The application can keep track of the available queue element count for notifications by following the procedure below: 
 
 Store initial queue element count in a variable. 
 Decrement the variable, which stores the currently available queue element count, by one when a call to this function returns NRF_SUCCESS . 
 Increment the variable, which stores the current available queue element count, by the count variable in BLE_GATTS_EVT_HVN_TX_COMPLETE event.

Increase characteristic value max length

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