increase the size of the buffer used to store the data of the received transmissions

[Frank_Godoy]

Hi, I am trying to increase the size of the data received by bluetooth, at the moment it allows me to receive a data up to 20 bytes, and I have been reading about how to configure for a larger data, and I have found in some parts that CONFIG_BT_L2CAP_RX_MTU, or CONFIG_BT_BUF_ACL_RX_SIZE is used, but both appear to me as undeclared symbols. 

I found this ticket, but it is not clear to me: https://devzone.nordicsemi.com/f/nordic-q-a/76585/extends-the-mtu-size-in-latest-zephyr?ReplyFilter=Answers&ReplySortBy=Answers&ReplySortOrder=Descending

im using nRF Connect 2.3.0

CONFIG_NCS_SAMPLES_DEFAULTS=y

CONFIG_BT=y
CONFIG_BT_DEBUG_LOG=y
CONFIG_BT_MAX_CONN=2
CONFIG_BT_MAX_PAIRED=2
CONFIG_BT_SMP=y
CONFIG_BT_L2CAP_TX_BUF_COUNT=6



CONFIG_BT_PERIPHERAL=y
CONFIG_BT_DEVICE_NAME="IPG PINNACLE"
CONFIG_BT_DEVICE_APPEARANCE=961

CONFIG_BT_BAS=y
CONFIG_BT_HIDS=y
CONFIG_BT_HIDS_MAX_CLIENT_COUNT=2
CONFIG_BT_HIDS_DEFAULT_PERM_RW_ENCRYPT=y
CONFIG_BT_GATT_UUID16_POOL_SIZE=40
CONFIG_BT_GATT_CHRC_POOL_SIZE=20

CONFIG_BT_CONN_CTX=y
CONFIG_BT_DIS=y
CONFIG_BT_DIS_PNP=y
CONFIG_BT_DIS_MANUF="NordicSemiconductor"
CONFIG_BT_DIS_PNP_VID_SRC=2
CONFIG_BT_DIS_PNP_VID=0x1915
CONFIG_BT_DIS_PNP_PID=0xEEEF
CONFIG_BT_DIS_PNP_VER=0x0100

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048

CONFIG_BT_SETTINGS=y
CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_FLASH_MAP=y
CONFIG_NVS=y
CONFIG_SETTINGS=y

CONFIG_DK_LIBRARY=y

[Vidar Berg]

Hi,

Are you getting an error/warning in the build output, or does it show as "undefined" in the editor when you try to add the symbols to your prj.conf? 

# ATT_MTU - 247
CONFIG_BT_L2CAP_TX_MTU=251
CONFIG_BT_BUF_ACL_RX_SIZE=251
CONFIG_BT_BUF_ACL_TX_SIZE=251

# Support max. Radio packet length
CONFIG_BT_CTLR_DATA_LENGTH_MAX=251

Related ticket:  Updating MTU Size for Tx and Rx with Android BLE Client  

Best regards,

Vidar

[Frank_Godoy]

I was getting that warning, but now I implemented the related ticket you provided, the program builds and runs without errors or warnings, but it is only receiving at most 20 bytes. I am sending the packet from the nrf connect mobile application.

CONFIG_NCS_SAMPLES_DEFAULTS=y

CONFIG_BT=y
CONFIG_BT_DEBUG_LOG=y
CONFIG_BT_MAX_CONN=2
CONFIG_BT_MAX_PAIRED=2
CONFIG_BT_SMP=y

CONFIG_BT_PERIPHERAL=y
CONFIG_BT_DEVICE_NAME="IPG PINNACLE"
CONFIG_BT_DEVICE_APPEARANCE=961

CONFIG_BT_BAS=y
CONFIG_BT_HIDS=y
CONFIG_BT_HIDS_MAX_CLIENT_COUNT=2
CONFIG_BT_HIDS_DEFAULT_PERM_RW_ENCRYPT=y
CONFIG_BT_GATT_UUID16_POOL_SIZE=40
CONFIG_BT_GATT_CHRC_POOL_SIZE=20


CONFIG_BT_BUF_ACL_RX_SIZE=251
CONFIG_BT_BUF_ACL_TX_SIZE=251
CONFIG_BT_CTLR_DATA_LENGTH_MAX=251
CONFIG_BT_L2CAP_TX_MTU=247
CONFIG_BT_L2CAP_TX_BUF_COUNT=6

CONFIG_BT_CONN_CTX=y
CONFIG_BT_DIS=y
CONFIG_BT_DIS_PNP=y
CONFIG_BT_DIS_MANUF="NordicSemiconductor"
CONFIG_BT_DIS_PNP_VID_SRC=2
CONFIG_BT_DIS_PNP_VID=0x1915
CONFIG_BT_DIS_PNP_PID=0xEEEF
CONFIG_BT_DIS_PNP_VER=0x0100

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048

CONFIG_BT_SETTINGS=y
CONFIG_FLASH=y
CONFIG_FLASH_PAGE_LAYOUT=y
CONFIG_FLASH_MAP=y
CONFIG_NVS=y
CONFIG_SETTINGS=y


CONFIG_DK_LIBRARY=y

[Vidar Berg]

Please register the "att_mtu_updated" callback to get notified when the ATT MTU is increased. 

...

void mtu_updated(struct bt_conn *conn, uint16_t tx, uint16_t rx)
{
	printk("Updated MTU: TX: %d RX: %d bytes\n", tx, rx);
}

static struct bt_gatt_cb gatt_callbacks = {
	.att_mtu_updated = mtu_updated
};

...

void main(void)
{ 
   ...
   	err = bt_enable(NULL);
	if (err) {
		error();
	}
	/* Callback must be registered after bt_enable() */
	bt_gatt_cb_register(&gatt_callbacks);

Also, what service are you trying to write to, and do you get any errors when trying to write more than 20 bytes to it?

[Frank_Godoy]

when 20 bytes are exceeded, no errors are displayed, only the data is not received.
The service I used is based on the example of peripheral hids keyboard, the battery service, see below.

static ssize_t write_blvl(struct bt_conn *conn, 
						  const struct bt_gatt_attr *attr,
			  			  const void *buf, 
						  uint16_t len, 
						  uint16_t offset,
						  uint8_t flags)
{
	
	if (offset + len > CMD_BUFFER_SIZE) {
		return BT_GATT_ERR(BT_ATT_ERR_INVALID_OFFSET);
	}

	memcpy(cmd_buffer + offset, buf, len);
	size_t current_cmd_size = offset + len;

	
	printk("\n");
	set_command_data(cmd_buffer[2]);
	printk("\nACK Package: ");
	for(int i = 0; i < current_cmd_size; i++){
		printk("%02x", cmd_buffer[i]);
		
		if(i+1 < current_cmd_size){
			printk("-");
		}
	}
	printk("\n-- End of command --\n");
	
	return len;
}
BT_GATT_SERVICE_DEFINE(bas,
	BT_GATT_PRIMARY_SERVICE(BT_UUID_BAS),
	BT_GATT_CHARACTERISTIC(BT_UUID_BAS_BATTERY_LEVEL,
			       BT_GATT_CHRC_READ | BT_GATT_CHRC_NOTIFY | BT_GATT_CHRC_WRITE,
			       BT_GATT_PERM_READ | BT_GATT_PERM_WRITE, read_blvl, write_blvl,
			       &cmd_buffer),
	BT_GATT_CHARACTERISTIC(BT_UUID_RESPONSE_COMM,
			       BT_GATT_CHRC_READ,
			       BT_GATT_PERM_READ | BT_GATT_PERM_WRITE, read_blvl, NULL,
			       &comm_response),
	
	BT_GATT_CCC(blvl_ccc_cfg_changed,
		    BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),
);

here you can see updated MTU, but still the same size.

[Vidar Berg]

The log shows that the ATT MTU did not get increased. Do you have another phone you can test with?