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]

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().

[Marshed]

I have used the 

add_char_params.is_defered_read   = 1;
characteristic_add()

and now I do get BLE_GATT_EVT_RW_AUTHORIZE_REQUEST, however the read_function at the client receives no data, and err of 14. 

am I missing some steps? how come when I add_char_params.is_defered_read is not set I can read the value with no error but when add_char_params.is_defered_read   = 1; I get error and hence no data at the client.

please assist. 

[Kenneth]

Do you remember to reply?

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.s132.api.v6.1.1%2Fgroup___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 

[Marshed]

Lets see if I get it correctly,

when you read with no authorization, you don't need to reply, bluetooth takes care of it by itself, but if you are reading with authorization you have to write a code for a reply?

If that is the case do you have an example I can start with?

[Kenneth]

Marshed said:

when you read with no authorization, you don't need to reply, bluetooth takes care of it by itself, but if you are reading with authorization you have to write a code for a reply?

Correct, I am not aware of any example, but you may just search through the projects for BLE_GATT_EVT_RW_AUTHORIZE_REQUEST to check if any use it.