Proper sequence to disconnect BLE

RE: Proper sequence to disconnect BLE

Hieu — Fri, 28 Jun 2024 08:52:57 GMT

Hi Xander,

[quote user="Xander To"]I have checked out the link you sent. I believe that writing with the response is the property required to ensure no data loss when a smartphone wants to send data to the MCU, and reading with indication is the property required to ensure no data loss when the MCU sends data to a smartphone, am I correct?[/quote]

Yes

[quote user="Xander To"]Furthermore, if I want a smartphone or any client-side to read the data from MCU without polling, I must add notify properties to the characteristic. So in the end, I must use read notify indication characteristic?[/quote]

Indication also let the client read without polling. It just requires a response from the client in the next connection event and is therefore slower than Notification.

Best regards,

Hieu

RE: Proper sequence to disconnect BLE

Xander To — Fri, 28 Jun 2024 01:31:07 GMT

Hi Hieu,

I have checked out the link you sent. I believe that writing with the response is the property required to ensure no data loss when a smartphone wants to send data to the MCU, and reading with indication is the property required to ensure no data loss when the MCU sends data to a smartphone, am I correct?

Furthermore, if I want a smartphone or any client-side to read the data from MCU without polling, I must add notify properties to the characteristic. So in the end, I must use read notify indication characteristic?

Best regards,

Xander

RE: Proper sequence to disconnect BLE

Hieu — Wed, 26 Jun 2024 12:21:29 GMT

Hi Xander,

Central and Peripheral are GAP concepts. When you are dealing with characteristics, you are dealing with GATT, and the roles are GATT Client and GATT Server.

In the vast majority of cases, the smartphone is the GAP Central and also the GATT Client, and a BLE device is the GAP Peripheral and also the GATT Server.

[quote user="Xander To"]1. If I want to send data from a smartphone to the MCU, and I want the write with the response to ensure the write command goes through successfully, the MCU must have a write with response characteristic properties?[/quote]

Almost yes. To be precise, the characteristic being written must have the Write with Response properties.

[quote user="Xander To"]2. If I want to send data from MCU to the smartphone, and ensure no data loss, the MCU must have a read indication characteristic properties? Smartphones don't have to poll data so that's why I used to read notify in the past. I'm not sure if I can replace read notify with just read indication.[/quote]

Read, Notify, and Indicate are three different independent properties. Independent meaning they are not in any way mutually exclusive or implicative.
They should be set according to what you want to enable and what you want to forbid.

[quote user="Xander To"]If possible, can you guide me with some resources to learn how to use these properties properly?[/quote]

This is pretty good: https://novelbits.io/bluetooth-gatt-services-characteristics/

Best regards,

Hieu

RE: Proper sequence to disconnect BLE

Xander To — Tue, 25 Jun 2024 20:05:13 GMT

Hi Hieu,

After doing more research about indication and notification, I'm getting more confused now. I'm not sure if I misunderstood anything but here is how I understand. Let's assume BLE peripheral is NRF MCU, and BLE central is a smartphone.
1. If I want to send data from a smartphone to the MCU, and I want the write with the response to ensure the write command goes through successfully, the MCU must have a write with response characteristic properties?
2. If I want to send data from MCU to the smartphone, and ensure no data loss, the MCU must have a read indication characteristic properties? Smartphones don't have to poll data so that's why I used to read notify in the past. I'm not sure if I can replace read notify with just read indication.

If possible, can you guide me with some resources to learn how to use these properties properly?

Best regards,

Xander

RE: Proper sequence to disconnect BLE

Hieu — Tue, 25 Jun 2024 12:02:17 GMT

Hi Xander,

BLE_GATTS_EVT_HVN_TX_COMPLETE will be generated when the notification has been sent. You can consider it a reference point to wait for before disconnecting.

Best regards,

Hieu

RE: Proper sequence to disconnect BLE

Hieu — Fri, 21 Jun 2024 20:41:32 GMT

Hi Xander,

I will have to get back to you next week on whether the notification will be sent for sure before the disconnect happen.

Your other question is rather on topic. If you want to ensure that the data is received by the smartphone, then you can use Indication instead of Notification. If very high throughput is not a concern, this is the best option.

See: How different BLE packet types influence throughput

Best regards,

Hieu