How to get 248 byte device name into the nRF51822 chip?

RE: How to get 248 byte device name into the nRF51822 chip?

Bill Siever — Sun, 20 Sep 2015 20:26:24 GMT

Just a minor clarification on Jan's comment: Attributes and Characteristics, like Device Name, can be longer than 31 bytes. In recent SDKs this can be done via Nordic's Long Write mechanism. Search the forum for Long Write for details.

RE: How to get 248 byte device name into the nRF51822 chip?

endnode — Sun, 20 Sep 2015 19:34:30 GMT

Hi Risto, Bill is correct. There are two places you can put "Device Name" in BLE "stack" (assuming you are talking about GAP Peripheral device implementing GATT Server stack):

GAP AD element within Advertising or Scan Response Data (there are two options: "Short Local Name" tag 0x08 or "Complete Local Name" tag 0x09).
Value of Device Name characteristic (standard BLE 16-bit UUID = 0x2A00) under Generic Access Profile Primary Service (standard BLE 16-bit UUID = 0x1800).

First place is limited by maximum length of Advertising or Scan Response packet (that's 31B by specification so when counting Tag and Length bytes of AD element encapsulation it's 29B for name itself). Second place is limited by GATT Value maximum defined as 512B but Nordic's GATT Server implementation inside Soft Device S110/S120/S130/S132 has limitation of 31B there anyway. Of course it's easy to define your own Primary Service and Characteristic where you can use full length of value field for your proprietary identification.

CHeers Jan

RE: How to get 248 byte device name into the nRF51822 chip?

Bill Siever — Sat, 19 Sep 2015 12:23:50 GMT

248 is the maximum length for the Local Name when using traditional bluetooth (BR/EDR), not bluetooth low energy (BLE). The nRF51/52 series are bluetooth low energy.

The Bluetooth Low Energy Specifications (BLUETOOTH SPECIFICATION Version 4.0 [Vol 6], Section 2.1 & Figure 2.1) show the packet format for Bluetooth Low Energy. A Link Layer packet only has 39 bytes for payload. (GAP & GATT messages will be a little less). More data can be sent by using more packets, but this doesn't allow one to advertise longer names.

RE: How to get 248 byte device name into the nRF51822 chip?

Risto — Sat, 19 Sep 2015 06:34:55 GMT

Yes, I mean the name actually contained in advertising packet. As I understand the chips as such do not limit the device name to 31 but support the Bluetooth standard 248. Maybe there are different SDKs?

RE: How to get 248 byte device name into the nRF51822 chip?

Bill Siever — Fri, 18 Sep 2015 23:54:23 GMT

Risto,

Just to clarify, are you referring to the name actually contained in advertising packet? It so, I believe you can only send full names that are ~29 bytes or the initial ~29 bytes of longer names. The specs for the GAP device name don't appear to have a length limit (other than the max characteristic size on BLE, which I think is 512 bytes), but it requires a connection to retrieve. Nordic's SDK appears to limit the string passed to sd_ble_gap_device_name_set() to 31 bytes. (infocenter.nordicsemi.com/index.jsp and the definition of BLE_GAP_DEVNAME_MAX_LEN).

For those interested, here are some possible workarounds that may work in some use-cases: Advertising a custom UUID can be used to identify products from a particular vendor. Custom advertising messages might be used to transfer a longer un-official name. And if a connection is required to retrieve the name anyway, the Device Information Service data (possible with custom data) may be a better choice for model/device data.