CLI Example - how to write a characteristic?

RE: CLI Example - how to write a characteristic?

awneil — Mon, 26 Oct 2020 11:07:12 GMT

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

What I was doing was:

Scan for devices
Connect to a device
Discover the Services
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.

RE: CLI Example - how to write a characteristic?

Hung Bui — Mon, 26 Oct 2020 10:32:34 GMT

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 ?

RE: CLI Example - how to write a characteristic?

awneil — Fri, 23 Oct 2020 15:49:18 GMT

[quote userid="2121" url="~/f/nordic-q-a/67533/cli-example---how-to-write-a-characteristic/276691#276691"]you will get the service UUID to use[/quote]

That wasn't the question!

[quote userid="6462" url="~/f/nordic-q-a/67533/cli-example---how-to-write-a-characteristic"]this seems to be missing anywhere to specify the Service UUID[/quote]

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?

RE: CLI Example - how to write a characteristic?

Hung Bui — Fri, 23 Oct 2020 15:29:04 GMT

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)