Hi,
I cannot find any documentation about Nimble connection events
scheduling. I have following scenario:
NRF52 Nimble is in dual role setting. Peripheral device connected to a
PC with at least BLE 4.2 and MTU more than 153B. Central is connected to
18 peripheral devices BLE 4.1 with MTU 27B.
Do you think that Nimble can keep interval window 12.5ms with the PC and
37.5ms with all peripherals?
My assumption are following:
* only one packet per each connection event
* send/receive 132B packet between NRF52 and PC each connection event
* send/receive 20B packet between NRF52 and peripheral each connection
event
I made following rough computation:
PC <-> NRF52: 132B data + 21B header => (153B * 8) / 1Mbps => 1224 uS +
150 uS IFR + 80 uS ACK + 150 uS IFR => 1604 uS * 2 (send/receive) =>
3208 uS
NRF52 <-> peripheral: 20B data + 21B header => (41B * 8) / 1Mbps =>
328uS + 150 uS IFR + 80 uS ACK + 150uS IFR => 708uS * 2 (send/receive)
=> 1416 uS
It means one big and six small packets should fit in each PC <-> NRF52
connection event 3208 + 6 * 1416 = 11 704 < 12.5ms interval window. For
18 peripherals it means 3 such cycles to serve them all therefore 37.5ms
interval window between NRF52 and a peripheral.
Are following parameters good to achieve this:
NRF52 <-> PC
static const struct ble_gap_conn_params ble_gap_conn_params_ideal = {
.scan_itvl = BLE_GAP_SCAN_FAST_INTERVAL_MIN,
.scan_window = BLE_GAP_SCAN_FAST_WINDOW,
.itvl_min = 10,
.itvl_max = 10,
.latency = 0,
.supervision_timeout = 500,
.min_ce_len = 5, // 3.208 / 0.625 = 5.1328
.max_ce_len = 6,
};
NRF52 <-> Peripheral
static const struct ble_gap_conn_params ble_gap_conn_params_ideal = {
.scan_itvl = BLE_GAP_SCAN_FAST_INTERVAL_MIN,
.scan_window = BLE_GAP_SCAN_FAST_WINDOW,
.itvl_min = 30,
.itvl_max = 30,
.latency = 0,
.supervision_timeout = 500,
.min_ce_len = 2, // 1.416 / 0.625 = 2.2656
.max_ce_len = 3,
};
Regards
Ondrej
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