LL_LENGTH_REQ & LL_LENGTH_RSP on nRF52840 with different TX and RX size

[Anton Fedorov]

Hello!

I am building Central app to read data from not a fully conformant BLE devices.

When I connect to device with my Android or Windows app, the connection establishes immediately. Connecting with Zephyr default stack lead device into "broken connection" mode (all I know, the status LED starts fast-blinking instead of steady light as it should be).

I have ruled out all other options, and the issue is -- the device requires that central confirm it's LL_LENGTH_REQ:

Peripheral => Central:
Control Opcode: LL_LENGTH_REQ (0x14)
Max RX octets: 251
Max RX time: 2120 microseconds
Max TX octets: 27
Max TX time: 328 microseconds

Phone & windows & TI BLE stack does that with ease, but I am failing to configure project to get the same on nRF52840. 

No matter how I set parameters in prj.conf:

CONFIG_BT_BUF_ACL_RX_SIZE

CONFIG_BT_BUF_ACL_TX_SIZE

CONFIG_BT_CTLR_DATA_LENGTH_MAX
(I've tried varied settings of 27 and 251 there)

And in child_image/hci_rpmsg.conf:

CONFIG_BT_CTLR_TX_BUFFER_SIZE=27

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

CONFIG_BT_RX_BUF_LEN=255

The generated response packet

Control Opcode: LL_LENGTH_RSP (0x15)
Max RX octets: 251
Max RX time: 2120 microseconds
Max TX octets: 251
Max TX time: 2120 microseconds

has RX and TX equals - either 251 or 27.

The current settings are:

CONFIG_BT=y

CONFIG_BT_CENTRAL=y

CONFIG_BT_SMP=y

CONFIG_BT_GATT_CLIENT=y

CONFIG_BT_GATT_DM=n

CONFIG_BT_CTLR_ADV_EXT=y

CONFIG_BT_CTLR_PHY_CODED=y

CONFIG_BT_USER_PHY_UPDATE=n

CONFIG_BT_SMP=y

CONFIG_BT_GATT_AUTO_UPDATE_MTU=n

CONFIG_BT_AUTO_PHY_UPDATE=n

CONFIG_BT_AUTO_DATA_LEN_UPDATE=n

CONFIG_BT_BUF_ACL_RX_SIZE=251

CONFIG_BT_BUF_ACL_TX_SIZE=27

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

CONFIG_BT_USER_DATA_LEN_UPDATE=y

CONFIG_BT_CTLR=y

# hci_rpmsg.conf -- but I really think this one is unused

CONFIG_BT_EXT_ADV=y

CONFIG_BT_CTLR_ADV_EXT=y

CONFIG_BT_CTLR_PHY_CODED=y

CONFIG_BT_CTLR_TX_BUFFER_SIZE=27

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

CONFIG_BT_RX_BUF_LEN=255

[Hung Bui]

Hi Anton, 
I'm glad that you found what trigger the peripheral. 
Regarding your question, the information I got from the team is that at this moment we don't support asymmetric DLE unfortunately. We will always match the RX time and TX time. We may support it in the future but I don't know when it will be implemented. 

[Anton Fedorov]

Thank you very much for the confirmation.