Send 16 bits instead of 8 bits over BLE

[Awi]

Hello,

I'd like to send 16 bits data over ble instead of 8 bits

gatts_value.offset = 0;
gatts_value.len = len;
gatts_value.p_value = data;

err_code = sd_ble_gatts_value_set(conn_handle, value_handle, &gatts_value);

for len I set the value to 2 and cast the 16 bits to 8 bits by (uint8_t*)data.

Unfortunately I get this error:

APP ERROR: 12, line: 105, file: src/bluetooth/base_service.c

EDIT: line 105 is err_code = sd_ble_gatts_value_set(conn_handle, value_handle, &gatts_value);

Please help me.

Thank you in advance

~Taz

[Stian Røed Hafskjold]

Can you please show us how you convert the 16 bits data too?
p_value is supposed to be a pointer to an uint_8 array. So you need to split the 16 bits into two bytes in an array. infocenter.nordicsemi.com/.../structble__gatts__value__t.html

[Awi]

I just cast is using (uint8_t *) But I figured, I might have to do something like

data = val>>8 then send then data=val then send again

the other side will have to interpret different too. Is that correct?

[Stian Røed Hafskjold]

If you want the attribute value to be two bytes (16 bits), set the len value to 2 and represent the data as an uint8_t array with size 2.

How you choose to split the 16 bits and put them in to the array is up to you, as long as the reciever is able to decode it.

Yes, the other side will have to decode this and represent it as needed.

[Awi]

So I tried doing this:

uint16_t val = 300;
static uint8_t data[2];
data[0] = (uint8_t)(val >> 8);
data[1] = (uint8_t)(val);
update_characteristic(conn_handle,value_handle, sizeof(data),(uint8_t*)data)

and in update_characteristic:

gatts_value.offset = 0;
gatts_value.len = len;
gatts_value.p_value = data;
err_code = sd_ble_gatts_value_set(conn_handle, value_handle, &gatts_value);
APP_ERROR_CHECK(err_code);

Still getting error at the app error check:

APP ERROR: 12, line: 105, file .....

What am I doing wrong?

[Stian Røed Hafskjold]

Error 12 is NRF_ERROR_DATA_SIZE. So a data size of 2 is probably too big for the characteristic. When you add the characterisic using the sd_ble_gatts_characteristic_add() function, you specify the attribute max length in the attr_char_value. Maybe this is set to 1. Look for attr_char_value.max_len or similar in the code.