BLE5 - Make payload size 200 bytes - the right way

[Michael]

Hello,

I try to configure two nrf52832 devices work with payload of 200 bytes (data should be 200 bytes, not the all ble packet).

I took ble_app_uart_c peripheral and central examples - for 20 bytes everything looks ok.

After that, I tried to understand and implement in my code the ble_app_att_mtu_throughput example, but without luck.

Where can I find the exact algorithm for the increasing the payload size?

My algorithm now:

Common definitions:

NRF_SDH_BLE_GATT_MAX_MTU_SIZE             defined for 247 bytes (in sdk_config.h)

BLE_GATT_ATT_MTU_DEFAULT                         defined to 204 bytes (in ble_gatt.h)

Central:

in function ble_evt_handler(ble_evt_t const * p_ble_evt, void * p_context) - the function handles all BLE events

- in event BLE_GAP_EVT_PHY_UPDATE_REQUEST

-- I define the 2MBPS speed:

ble_gap_phys_t const phys =
 {
       .rx_phys = BLE_GAP_PHY_2MBPS,
       .tx_phys = BLE_GAP_PHY_2MBPS,
};
sd_ble_gap_phy_update(p_ble_evt->evt.gap_evt.conn_handle, &phys);

in function gatt_init() - the function initiates the gatt library

- nrf_ble_gatt_init(&m_gatt, gatt_evt_handler);

- nrf_ble_gatt_att_mtu_central_set(&m_gatt, BLE_GATT_ATT_MTU_DEFAULT); //to 204 bytes

in function data_len_ext_set() - the function should set the new MTU size. the function placed in main() function, after all initializations, but before scan_start() call

- nrf_ble_gatt_data_length_set(&m_gatt, BLE_CONN_HANDLE_INVALID, 200 + L2CAP_HDR_LEN);  - according to example. 200 - needed payload, L2CAP_HDR_LEN - defined as 4

in function conn_evt_len_ext_set() - not sure, but looks that the function enables length increasing option in the stack, called just after the data_len_ext_set() function

- memset(&opt, 0x00, sizeof(opt));
- opt.common_opt.conn_evt_ext.enable = 1;
- sd_ble_opt_set(BLE_COMMON_OPT_CONN_EVT_EXT, &opt);

Peripheral

in ble_evt_handler(ble_evt_t const * p_ble_evt, void * p_context) - the function handles all BLE events

- I define the 2MBPS speed:

ble_gap_phys_t const phys =
 {
       .rx_phys = BLE_GAP_PHY_2MBPS,
       .tx_phys = BLE_GAP_PHY_2MBPS,
};

- in event BLE_GAP_EVT_CONNECTED

-- sd_ble_gap_phy_update(p_gap_evt->conn_handle, &phys); //request for 2MBPS

- in event BLE_GAP_EVT_PHY_UPDATE_REQUEST

-- sd_ble_gap_phy_update(p_ble_evt->evt.gap_evt.conn_handle, &phys);

- in event BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST

-- memset(&dl_params, 0, sizeof(ble_gap_data_length_params_t));

-- sd_ble_gap_data_length_update(p_ble_evt->evt.gap_evt.conn_handle, &dl_params, NULL);

in function gatt_init() - the function initiates the gatt library

- nrf_ble_gatt_init(&m_gatt, gatt_evt_handler);

- nrf_ble_gatt_att_mtu_periph_set(&m_gatt, BLE_GATT_ATT_MTU_DEFAULT); //to 204 bytes

in function data_len_ext_set() - the function should set the new MTU size. the function placed in main() function, after all initializations, but before ble_advertising_start(&m_advertising, BLE_ADV_MODE_FAST); call

- nrf_ble_gatt_data_length_set(&m_gatt, BLE_CONN_HANDLE_INVALID, 200 + L2CAP_HDR_LEN);  - according to example. 200 - needed payload, L2CAP_HDR_LEN - defined as 4

in function conn_evt_len_ext_set() - not sure, but looks that the function enables length increasing option in the stack, called just after the data_len_ext_set() function

- memset(&opt, 0x00, sizeof(opt));
- opt.common_opt.conn_evt_ext.enable = 1;
- sd_ble_opt_set(BLE_COMMON_OPT_CONN_EVT_EXT, &opt);

So, is it looks ok? Some mistakes that you could point me on? Something is missing?

Thanks a lot!

[Michael]

I try to extend the MTU size and get the next prints:

: Trying to set length

-max_rx_octest: 251

-max_tx_octets: 251

sd_ble_gap_data_length_update() (request) on connection 0x0 returned unexpected value 0x13.

Error NRF_ERROR_RESOURCES

-tx_payload_limited_octets: 101

-rx_payload_limited_octets: 101

What is payload? Is it L2CAP+OpCode+AttributeHandle+AttPayload or just AttPayload?

Why the payload is limited to 101 bytes?

[Kenneth]

You will likely need to adjust NRF_SDH_BLE_GAP_EVENT_LENGTH = 5 (or more) to allow longer packets, because this will reserve more time for the radio event. I expect '101' message you get to be the max with NRF_SDH_BLE_GAP_EVENT_LENGTH = 3.  Also, with max octets = 251 the max used by the application is 247, the remaining 4 is L2CAP header.

APP +  SD is the local firmware running on the nRF52832, while PEER is whoever is on the other side of the connection.

[Michael]

Hello,

Thank you for your answer!

When I'm increasing the NRF_SDH_BLE_GAP_EVENT_LENGTH to 5 or more I get a NRF_ERROR_NO_MEM at nrf_sdh_ble_enable function (please see the attached image)

How I should to increase the memory?

[Kenneth]

Presuming you are using Keil you can for instance open 'Options for Target' and modify the IRAM1 Start and Size required by the softdevice, if you enable logging you should be able to find the recommended settings for both parameters in nrf_sdh_ble_enable().

[Michael]

Hello,

I'm using Segger Embedded Studio :)

Kenneth said:

if you enable logging you should be able to find the recommended settings for both parameters in nrf_sdh_ble_enable().

This part of the answer I don't understand. In attached picture I can see recommendations for adjusting the start address and the size, is it non-correct values? Should I find another values?

[Kenneth]

You need to adjust the project settings with the new values for RAM start and size, see below screenshot as en example where you can find the variables in question.

[Michael]

Hello Kenneth,

Thank you very very much for your help!

It helped!!!

For now I'm trying to re-transmit 200 bytes packets! Thank you!