ble_app_rscs

[Marshed]

I have nRF52832 running ble_app_rscs as a server, sending notification to the client every hour. I know that the client can read the values also by sending bt_gatt_read to the server and the server will reply instantly with the values. However this value corresponds to the latest measurements conducted by the server, and it could be a while ago. Is there away of sending a message from the client to server so that the server can actually do the measurements instantly? In other words can the client initiate the server to sample its sensors and update gatt instead of waiting for its timer?

Please assist. 

[Kenneth]

Hi,

There should be no problem to implement this in the application running the server. For instance you may on a GATT write to the characteristic send a notification on demand, e.g. check out the message sequence charts:

https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v6.1.1/group___b_l_e___g_a_t_t_s___w_r_i_t_e___r_e_q___n_o___a_u_t_h___m_s_c.html 

In other words when the application receive a BLE_GATTS_EVT_WRITE event it may trigger a measurement, which again can trigger a notification with the latest measurement.

Alternatively you may also implement GATT read with authorization, in such case the application running the server will receive an BLE_GATT_EVT_RX_AUTHORIZE_REQUEST each time the peer try to read the characteristic:

https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v6.1.1/group___b_l_e___g_a_t_t_s___r_e_a_d___r_e_q___a_u_t_h___m_s_c.html?cp=3_4_2_1_2_4_3_13

This can also be used for the application to trigger a measurement, which again can trigger a notification with the latest measurement.

Best regards,
Kenneth

[Marshed]

Hi, 

Can you do that with GATT READ? is there a BLE_GATTS_EVT_READ? and can i use it to trigger a measurements?

[Kenneth]

No, but it's for all practical purposes similar, you will get an BLE_GATT_EVT_RX_AUTHORIZE_REQUEST event that allow the application to decide whether or not to allow the peer to read the characteristic or not. But in your case you also use it to trigger a measurement.Best regards,
Kenneth

[Marshed]

now the question remains how do I implement GATT read with authorization, as in the client side I only see bt_gatt_read, is it something you do on the server side? 

if it is how can I enable this as for now i do not get BLE_GATT_EVT_RX_AUTHORIZE_REQUEST when i try to read on the server. 

[Kenneth]

This is handled on the server yes, for instance:

attr_md.rd_auth = 1;       
attr_md.wr_auth = 0;

Before calling sd_ble_gatts_characteristic_add().

My suggestion may be further improved by: So when the application receive the RW_AUTHORIZE_REQUEST, then it can execute the measurement, and write the data using sd_gle_gatts_rw_authorize_reply(). I think you can have up to 30 seconds to do this.

Best regards,
Kenneth

[Marshed]

I am using ble_app_rscs example and I can't seem to find where sd_ble_gatts_characteristic_add() is called, and hence where i can initialize attr_md.rd_auth to 1. 

please assist

[Marshed]

I am using ble_app_rscs example and I can't seem to find where sd_ble_gatts_characteristic_add() is called, and hence where i can initialize attr_md.rd_auth to 1. 

I have also used bt_gatt_write and this returns error number 3, but still no BLE_GATT_EVT_RW_AUTHORIZE_REQUEST is called. 

can you assist?

[Kenneth]

It's called a few places if you search for sd_ble_gatts_characteristic_add() in the project, but typically it is wrapped by characteristic_add(), so you may use:

add_char_params.is_defered_read   = 1;
characteristic_add()

that should then set rd_auth to 1 before calling sd_ble_gatts_characteristic_add().