Clearing characteristic value

RE: Clearing characteristic value

iQd — Thu, 04 Oct 2018 09:43:07 GMT

Thank you, it seems I was missing the VLEN, it fixed the issue when I added it and set it to 1.

RE: Clearing characteristic value

Simon — Thu, 04 Oct 2018 09:35:08 GMT

Let me try to give you an intuition of how it works.

When running the SVCall sd_ble_gatts_characteristic_add(..) one of the arguments is the GATT attribute structure p_attr_char_value. That structure contains respectively the length and the value of the characteristics:

init_len and max_len gives the length in bytes
*p_value points to the attribute data

What happens if init_len and max_len is set to 4? Then the length is 4*(8 bits) = 32 bits, which can store numbers from 0 up to (2³²-1), or (0x)0 up to (0x)FFFF FFFF.

If you set the value equal to (0x)0201 0022 and the length equal to 4 then the following value will show up in nRF Connect: (0x) 22-00-01-02. Notice how the order is switched, the last byte is written first and so on.

Best regards, Simon.

RE: Clearing characteristic value

Richard D. — Wed, 26 Sep 2018 19:07:15 GMT

To change the characteristic value length to a single byte, you need to declare the characteristic as a variable-length.

Assuming you're using sd_ble_gatts_characteristic_add(), use characteristic metadata vlen = 1