How is the size of a characteristic set in Zephyr?

[DiBosco]

Am making a project based on NUS central demo and I can connect to our remote unit with the 52840DK, I can send data over a UART into it and I can get data out which is received on the remote BLE node.

I'd like to, well, need to, change the TX and RX characteristics to be 240 bytes in size.

I have seen here:

devzone.nordicsemi.com/.../extends-the-mtu-size-in-latest-zephyr

Someone talking about the maximum overall size (although I don't understand what he's saying in the answer).

Where are these used? ie What file would this be in?

CONFIG_BT_BUF_ACL_RX_SIZE instead of CONFIG_BT_L2CAP_RX_MTU (comes from l2cap.h, 

#define BT_L2CAP_RX_MTU (CONFIG_BT_BUF_ACL_RX_SIZE - BT_L2CAP_HDR_SIZE)

And this:

Max payload size of adv_data with extended advertizement


I'd expect to see it in this:

/* UART Service Declaration */

BT_GATT_SERVICE_DEFINE(nus_svc,

BT_GATT_PRIMARY_SERVICE(BT_UUID_NUS_SERVICE),

BT_GATT_CHARACTERISTIC(BT_UUID_NUS_TX,

BT_GATT_CHRC_NOTIFY,

#ifdef CONFIG_BT_NUS_AUTHEN

BT_GATT_PERM_READ_AUTHEN,

#else

BT_GATT_PERM_READ,

#endif /* CONFIG_BT_NUS_AUTHEN */

NULL, NULL, NULL),

BT_GATT_CCC(nus_ccc_cfg_changed,

#ifdef CONFIG_BT_NUS_AUTHEN

BT_GATT_PERM_READ_AUTHEN | BT_GATT_PERM_WRITE_AUTHEN),

#else

BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),

#endif /* CONFIG_BT_NUS_AUTHEN */

BT_GATT_CHARACTERISTIC(BT_UUID_NUS_RX,

BT_GATT_CHRC_WRITE |

BT_GATT_CHRC_WRITE_WITHOUT_RESP,

#ifdef CONFIG_BT_NUS_AUTHEN

BT_GATT_PERM_READ_AUTHEN | BT_GATT_PERM_WRITE_AUTHEN,

#else

BT_GATT_PERM_READ | BT_GATT_PERM_WRITE,

#endif /* CONFIG_BT_NUS_AUTHEN */

NULL, on_receive, NULL),

);

In good old SES we had what seems logical to me in this:

   attr_char_value.max_len   = TX_LEN;


    err_code = sd_ble_gatts_characteristic_add( exlrt_service.service_handle,
                                                &char_md,
                                                &attr_char_value,
                                                handle );

So what's the equivalent with Zephyr please? And do I have to add something to the proj file to say what the max allowable size is?

[DiBosco]

OK thanks again, I'll see whether I can sort this out with defining my own service and knit it in with the central project.

I really detest macros and never, ever use them because they obfuscate code too much, but, in this case, I don't need to  understand what's going on under the hood, so I should just suck it up!

[DiBosco]

I'm still struggling with this.

It tells me there's an error if I use this in prj.conf

CONFIG_BT_L2CAP_RX_MTU=247

If I do this:

static uint8_t device_info[240];

static uint8_t send_info[240];

/* UART Service Declaration */

BT_GATT_SERVICE_DEFINE(nus_svc,

BT_GATT_PRIMARY_SERVICE(BT_UUID_NUS_SERVICE),

BT_GATT_CHARACTERISTIC(BT_UUID_NUS_TX,

BT_GATT_CHRC_NOTIFY,

#ifdef CONFIG_BT_NUS_AUTHEN

BT_GATT_PERM_READ_AUTHEN,

#else

BT_GATT_PERM_READ,

#endif /* CONFIG_BT_NUS_AUTHEN */

NULL, NULL, send_info),

BT_GATT_CCC(nus_ccc_cfg_changed,

#ifdef CONFIG_BT_NUS_AUTHEN

BT_GATT_PERM_READ_AUTHEN | BT_GATT_PERM_WRITE_AUTHEN),

#else

BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),

#endif /* CONFIG_BT_NUS_AUTHEN */

BT_GATT_CHARACTERISTIC(BT_UUID_NUS_RX,

BT_GATT_CHRC_WRITE |

BT_GATT_CHRC_WRITE_WITHOUT_RESP,

#ifdef CONFIG_BT_NUS_AUTHEN

BT_GATT_PERM_READ_AUTHEN | BT_GATT_PERM_WRITE_AUTHEN,

#else

BT_GATT_PERM_READ | BT_GATT_PERM_WRITE,

#endif /* CONFIG_BT_NUS_AUTHEN */

NULL, on_receive, device_info),

);

I seem to be able to write long characteristics *IN* to the

peripheral_uart from a phone, but if I try to send larger chunks of

data out to the phone from the nrf I get an error -12 which the

source code tells me is:

#define ENOMEM 12 /* Out of memory */

So what is the issue here please?

[Susheel Nuguru]

At this point, I have to request you to give me your project so that I understand little better on the configs and other setup you have. Can you please attach you project so that I can test and try to figure out if we need to increase some buffer sizes in the configuration file.