Zephyr BLE issues

RE: Zephyr BLE issues

Amanda Hsieh — Tue, 05 Aug 2025 18:35:11 GMT

[quote user="rsf_pn"]

#CONFIG_BT_CTLR_PHY_2M=y

#CONFIG_BT_CTLR_PHY_CODED=y

for some reason my main loop is not executed anymore if i add these two lines back in.

[/quote]

It's not clear what might have caused the issue, but you can refer to https://github.com/nrfconnect/sdk-nrf/tree/main/samples/bluetooth/throughput for the settings and coding.

[quote user="rsf_pn"]and i don't get the MTU values i thought MTU can be maximum 251 bytes with 244 bytes usable data for bluetooth 5. what does 498 mean. can i really use 498 bytes every connection interval?[/quote]

MTU of 498 means the maximum size of a single ATT operation, but not a single on-air packet. The actual on-air packet size is limited by data length up to 251 bytes, while the actual payload that you can send is a maximum of 244 bytes. This is because the 251-byte Data PDU payload needs an L2CAP Header of 4 bytes, and an Attribute header of 3 bytes. This leaves you with 251 – 4 – 3 = 244 bytes that you can actually populate with payload data.

RE: Zephyr BLE issues

rsf_pn — Mon, 04 Aug 2025 19:42:28 GMT

changing the connection paramters worked perfectly fine following the guide.

i've set the following settings in my proj.conf file (looked at the guide and throughput example for the macros)

CONFIG_BT_PERIPHERAL_PREF_MIN_INT=6
CONFIG_BT_PERIPHERAL_PREF_MAX_INT=24
CONFIG_BT_PERIPHERAL_PREF_LATENCY=0
CONFIG_BT_PERIPHERAL_PREF_TIMEOUT=400
CONFIG_BT_GAP_AUTO_UPDATE_CONN_PARAMS=y
CONFIG_BT_USER_PHY_UPDATE=y

CONFIG_BT_MAX_CONN=1
CONFIG_BT_MAX_PAIRED=1

CONFIG_BT_BUF_ACL_RX_SIZE=502
CONFIG_BT_ATT_PREPARE_COUNT=2
CONFIG_BT_ATT_TX_COUNT=10
CONFIG_BT_L2CAP_TX_MTU=498
CONFIG_BT_L2CAP_DYNAMIC_CHANNEL=y
CONFIG_BT_CONN_TX_MAX=10
CONFIG_BT_BUF_ACL_TX_COUNT=10
CONFIG_BT_BUF_ACL_TX_SIZE=502

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251
CONFIG_BT_CTLR_PHY_2M=y
CONFIG_BT_CTLR_PHY_CODED=y
CONFIG_BT_CTLR_SDC_MAX_CONN_EVENT_LEN_DEFAULT=4000000

and called the required commands from the guide.

in the debug logs i can see that the connection interval is set correctly, phy is updated and mtu is updated.

- BLE connected

PHY updated. New PHY: 2M
Connection interval: 24 units (30 ms)
Connection latency: 0
Supervision timeout: 720 ms
MTU: 23
UATT MTU: 23

Connection interval: 24 units (30 ms)
Connection latency: 0
Supervision timeout: 4000 ms
MTU: 498
UATT MTU: 498

Only two things that i still don't understand.

#CONFIG_BT_CTLR_PHY_2M=y

#CONFIG_BT_CTLR_PHY_CODED=y

for some reason my main loop is not executed anymore if i add these two lines back in.

and i don't get the MTU values i thought MTU can be maximum 251 bytes with 244 bytes usable data for bluetooth 5. what does 498 mean. can i really use 498 bytes every connection interval?

thanks for your advice

RE: Zephyr BLE issues

Amanda Hsieh — Mon, 04 Aug 2025 16:53:43 GMT

[quote user="rsf_pn"]can i also set the parameters as ble peripheral or only as central device?[/quote]

That course demonstrates setting the parameters on the ble peripheral side, and that will trigger the negotiation with the central device in the connection. so you may not get the full bytes that you request. The device that supports the shortest data length will have the final say.

RE: Zephyr BLE issues

rsf_pn — Mon, 04 Aug 2025 15:02:55 GMT

Thanks for the reply my current setup is:
nRF Connect SDK v3.0.2
nRF Connect SDK Toolchain v3.0.2
Zephyr OS v4.0.99

1. i see so i guess the issue is that i tried to run it from the callback.
2. im using the nrf52840 dongle and running it as a Bluetooth peripheral. can i also set the parameters as ble peripheral or only as central device?

RE: Zephyr BLE issues

Amanda Hsieh — Mon, 04 Aug 2025 14:31:49 GMT

Hi,

[quote user=""]I'm currently exploring BLE using zephyr and faced some issues.[/quote]

Are you using vanilla Zephyr? If so, please use nRF Connect SDK (NCS) since our support is based on NCS.

[quote user=""]1. id like to restart advertising after disconnecting from a device. I tried different approaches like stopping advertising and starting it again. stopping advertising, disabling bluetooth, enabling and starting it again but it always results in the same error. I added some error logs for debugging. I always get error code -12 but don't know how to resolve it.[/quote]

Check out this post.

[quote user=""]2. how do I max the ble data rate?[/quote]

Check out this course: https://academy.nordicsemi.com/courses/bluetooth-low-energy-fundamentals/lessons/lesson-3-bluetooth-le-connections/topic/blefund-lesson-3-exercise-2/

Regards,
Amanda H.