CLI Example - how to write a characteristic?

[awneil]

This (in SDK v17.0.2): 

Experimental: BLE Interactive Command Line Interface Example

https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/ble_sdk_app_interactive.html

The documentation says:

:
:
│
├── gatt
│   ├── characteristics <address> <service uuid> Discover service characteristics.
│   │
│   :
│   :
│   │
│   └── write <sub_cmd> Write a characteristic value.
│       ├── command <address> <char uuid> <value> Use a Write Command.
│       └── request <address> <char uuid> <value> Use a Write Request.
:
:

But this seems to be missing anywhere to specify the Service UUID.

If I just enter the Characteristic UUID, as suggested, it says, "The selected service does not contain the characteristic"

So how does one "select" a Service ?

[Hung Bui]

Hi Andrew,

The Service UUID is discovered and the base is added automatically as far as I know. So what you need to do is to call "gatt services <device>" 

It will discover the services. After that you will get the service UUID to use. In the following screenshot I tested with ble_app_uart : 

(I forgot to type the service UUID on the first trial)

[awneil]

Hung Bui said:

you will get the service UUID to use

That wasn't the question!

awneil said:

this seems to be missing anywhere to specify the Service UUID

The question is: how/where do I specify the Service UUID - as the documentation for the 'gatt write' command does not mention it.

The documentation for the 'gatt write' command only mentions <char uuid> - so where/how should the <service uuid> be specified?

[Hung Bui]

Hi Andrew, 

It seems that we don't support having multiple characteristics with same (short) UUID. 
This is the struct to handle characteristics in the interactive firmware: 

typedef struct
{
    ble_uuid_t            uuid;              /**< UUID of the characteristic. */
    uint16_t              decl_handle;       /**< Handle of the characteristic declaration. */
    uint16_t              value_handle;      /**< Handle of the characteristic value. */
    uint16_t              cccd_desc_handle;  /**< Handle of the CCCD descriptors. */
    ble_gatt_char_props_t char_props;        /**< GATT Characteristic Properties. */
} char_data_t;

I would consider it's a limitation of the interactive example. 

I don't have any issue with writing to the characteristic using only the characteristic UUID. Could you try to test with the ble_app_uart example ? 

[awneil]

Looking back through my logs, I can see some messages saying, "Too many characteristics discovered".

What I was doing was:

1. Scan for devices
2. Connect to a device
3. Discover the Services
4. For each Service, discover the Characteristics

So, I guess, the Characteristic I then tried to write had just got "lost" among the "Too many characteristics discovered" ?

If, instead, I just discover Characteristics for the one Service I require, the write then works.