l2cap implementation on nrf5340

[manikandan]

hello 

i have been using nrf5340 with ncs 1.9.1 i want to enable psm over l2cap in our firmware

# Using L2CAP library, we are able to connect, start recording and ask device to send audio data recorded. This is done similar to GATT existing implementation i know that the currently valid values for LE PSMs are 0x0001 - 0x007f for fixed Bluetooth SIG-defined services, and 0x0080 - 0x00ff for dynamic "custom” services as we don’t have implementation of PSM in firmware, we are unable to utilize L2CAP using current firmware due to which it is failing to open L2CAP channel and and unknown identifier error is streamed to device  may i know how can i add these values i using this to send the data to central  bt_gatt_notify_uuid do i need to change this api or configuration changes is enough

my prof.con app

#Enable MTU negotiation

CONFIG_BT_DATA_LEN_UPDATE=y

#Maximum supported L2CAP MTU for L2CAP buffers

CONFIG_BT_BUF_ACL_RX_SIZE=251

CONFIG_BT_BUF_ACL_TX_SIZE=251

# AG added

CONFIG_BT_L2CAP_TX_MTU=251  

# AG added

#CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

CONFIG_BT_L2CAP_TX_BUF_COUNT=16

# ATT and GATT options

#  30 ms(24) -> AG CHANGED -> 10ms(8)

CONFIG_BT_PERIPHERAL_PREF_MIN_INT=6

# 100 ms(80) -> AG CHANGED -> 12.5ms(10)

CONFIG_BT_PERIPHERAL_PREF_MAX_INT=9

CONFIG_BT_USER_DATA_LEN_UPDATE=y

CONFIG_BT_USER_PHY_UPDATE=y

CONFIG_BT_BUF_ACL_RX_SIZE=502

CONFIG_BT_ATT_PREPARE_COUNT=2

CONFIG_BT_L2CAP_TX_BUF_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

hci_rpmsg.con 

CONFIG_BT_BUF_ACL_TX_SIZE=251
CONFIG_BT_CTLR_DATA_LENGTH_MAX=251
CONFIG_BT_BUF_ACL_RX_SIZE=251

CONFIG_BT_MAX_CONN=2

may i know how to implement psm in our firmware 

[Hung Bui]

Hi Manikandan, 
Could you give me some more information about the issue you have ? 
Which PSM you tried to use?  I assume you have tested with a PSM higher than 0x7F ? 
Could you show the code ? I assume you used the APIs listed here: https://docs.zephyrproject.org/apidoc/latest/group__bt__l2cap.html ? 

My assumption is that you have tested with the normal ATT communication and the throughput was not enough so that you want to use L2CAP connection oriented channel ? 

[manikandan]

audio_udp_custom.zipi have used this psm 0x0055 i have attached my code kindly check my main.c prof.conf and initBLE() function i have only integrated code  i have attached that kindly check and get back to me

static int l2cap_accept(struct bt_conn *conn, struct bt_l2cap_chan **chan)
{
	return -ENOSYS;
}

static struct bt_l2cap_server test_server = {
	.accept		= l2cap_accept,
};

static struct bt_l2cap_server test_fixed_server = {
	.accept		= l2cap_accept,
	.psm		= 0x007f,
};

static struct bt_l2cap_server test_dyn_server = {
	.accept		= l2cap_accept,
	.psm		= 0x0055,
};

static struct bt_l2cap_server test_inv_server = {
	.accept		= l2cap_accept,
	.psm		= 0xffff,
};
//added this in ble_init
void test_l2cap_register(void)
{



	/* Attempt to register server with dynamic PSM */
	bt_l2cap_server_register(&test_dyn_server);



}

[Hung Bui]

Hi Manikandan, 

We currently don't have an example on how to use L2CAP channel. But could you let us know what kind of error you have ? 
How did you test ? I saw that you called test_l2cap_register() before the connection has been established. I don't think it's the way to go. 
The L2CAP connection oriented channel should be established after the connection has been created. 

Could you answer my question regarding why you want to use L2CAP channel instead of normal ATT ? 

[manikandan]

hello,

i am getting unknown identifier error when i tired to use l2cap layer

yes i want to increase the throughput .. where should i call the test_l2cap_register() in our firmware to enable l2cap correctly

regards

manikandan 

[Hung Bui]

Hi Manikandan, 

I'm checking internally if we have any example using L2CAP. But as far as I can see we don't have anything right now. 
Due to reduced staff in the summer, there will be some delay in our response. I'm sorry for that. 

[manikandan]

ok if thers is no example right now can you tell me what are the changes i should do in our firmware to get the l2cap working i will try that in the mean you can look for examples\

regards

manikandan v

[Hung Bui]

Hi Manikandan, 

We actually have example that uses L2CAP. You can take a look at the central_otc and the peripheral_ots. They use L2CAP channel under the hood to transfer object. You can find how L2CAP APIs are called inside ots_l2cap.c 
Also check if the example can actually do the job that you are looking for. It should have better throughput than normal ATT data. 

Another place you may want to take a look is inside \zephyr\tests\bsim\bluetooth\host\l2cap. This is where we have the projects for testing L2CAP. 

[manikandan]

hello,

how can i use a static uuid with l2cap and establish a connection and then a genrate a channel using static uuid and send a string like hello world and then receive it on central i have central working in python i want to know how can i implement this on nrf5340 periperal that peripheral_ots not helping

[Hung Bui]

Hi,

I'm not so sure you really need L2CAP channel. Have you tested with the peripheral_uart sample ? You can send a string to the phone or your central device on PC via GATT. I would suggest to test with the phone first before testing with the python app.