How to increase Data Rate

RE: How to increase Data Rate

Sigurd — Fri, 09 Jun 2017 13:35:15 GMT

Actually the ble_app_uart in SDK 13 will by default try to enable DLE, and set it to NRF_BLE_GATT_MAX_MTU_SIZE + LL_HEADER_LEN. But you need to check the log to see if it was successfully increased (i.e. if the iPad accepted the increase or not.). As mentioned earlier, if you set the NRF_LOG_DEFAULT_LEVEL to DEBUG (#define NRF_LOG_DEFAULT_LEVEL 4 in sdk_config.h), you should be able to see the parameters that is negotiated between the central and peripheral.

If DLE is not support on the iPad, you will see the following values in the log:

nrf_ble_gatt:DEBUG:max_rx_octets: 27
nrf_ble_gatt:DEBUG:max_tx_octets: 27

Unfortunately, I believe that many iOS devices does not support DLE, so this will limit your data-rate / throughput you can achieve. But you will have to check what values the max_rx_octets/max_tx_octets is set to.

RE: How to increase Data Rate

Ferhat B — Wed, 07 Jun 2017 07:06:37 GMT

First of all I couldnt find where to make DLE on.

Im sending 126 bytes in one pack now. It not working over 158. I tried 147 bytes working fine.

For now with 126bytes in one pack;
---> #define NRF_BLE_GATT_MAX_MTU_SIZE 158
---> 1nrf_ble_gatt_att_mtu_periph_set(&m_gatt, 150);
---> #define BLE_GATT_ATT_MTU_DEFAULT 23

I tried several values for INTERVALS for definitions below, For example i tested 7.5 as min and 20 as max. I didnnt get a positive effect.

#define MIN_CONN_INTERVAL MSEC_TO_UNITS(20, UNIT_1_25_MS)
#define MAX_CONN_INTERVAL MSEC_TO_UNITS(75, UNIT_1_25_MS)

My problem is;

Im sampling 16byte data at 500Hz. (I have some additional data but these important)
500Hz makes 2ms interval for sampling. (1/500)
Below 158 ATT MTU size, i can make 8 pack x 16 bytes = 128bytes
So sending interval became 8x2ms = 16ms
If i can send every 128bytes evey 16ms, all became perfect.
Im using iPad Air2 now but later i will use different options.

RE: How to increase Data Rate

Sigurd — Tue, 06 Jun 2017 13:22:50 GMT

Have you turned on DLE(Data length extension) ? What ATT MTU value are you using ? What connection interval value are you getting from the iPad?

RE: How to increase Data Rate

Ferhat B — Tue, 06 Jun 2017 06:47:08 GMT

Hi Sigurd, do you have any comment ?

RE: How to increase Data Rate

Ferhat B — Fri, 02 Jun 2017 13:52:23 GMT

Hi Sigurd

I have 20bytes pack and i collect them 120bytes (6*20) and send totaly.
This works fine every 24ms interval.
Bu i need to send 12ms interval evey 120byte pack and its not working vell. Im using ipad air2 for monitring. Its missing packets.

RE: How to increase Data Rate

Sigurd — Fri, 19 May 2017 08:31:46 GMT

Yes, smartphones/tablet typically supports between 4-6 packets per connection interval. If the smartphone/tablet supports ATT MTU 158 bytes, then you can set m_ble_nus_max_data_len to 158. This is done automatically for you in the function gatt_evt_handler().

“In soft device document is see for client Att MTU 23 and 7.5ms”. It can be set to up-to 247. See table 2 here.

Q: I want to transfer 120bytes one time, is it possible?

A: Yes, this is possible as long as the smartphone/tablet also support it.

Also see this answer.

RE: How to increase Data Rate

Ferhat B — Wed, 17 May 2017 08:52:31 GMT

I want to transfer 120bytes one time, is it possible. How can i do it, i coulndt achieve.

RE: How to increase Data Rate

Ferhat B — Tue, 16 May 2017 13:14:02 GMT

Does the soft device send 6 pack together.
How much time ble sending (sd_ble_gatts_hvx) stops uart hanling.
I think the problem is uart waiting while ble sending.

About ATT MTU what is the maximum value, how much i can make "m_ble_nus_max_data_len" May i send 158bytes in one pack. In soft device document is see for client Att MTU 23 and 7.5ms

RE: How to increase Data Rate

Sigurd — Tue, 16 May 2017 11:52:46 GMT

Yes, the BLE_GATT_ATT_MTU_DEFAULT is 23, but if you use the ble_app_uart example in sdk 13, you have the m_ble_nus_max_data_len that is updated after ATT MTU exchange with the central. In the function gatt_init() in main.c we are trying to increase the ATT MTU to 64.

RE: How to increase Data Rate

Ferhat B — Tue, 16 May 2017 11:50:40 GMT

Do you mean 64 in below as ATT MTU
err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, 64);

RE: How to increase Data Rate

Ferhat B — Tue, 16 May 2017 11:46:57 GMT

Yes use SDK 13
BLE_GATT_ATT_MTU_DEFAULT 23
ble_hrs_heart_rate_measurement_send >> 20 bytes as pack length

RE: How to increase Data Rate

Sigurd — Tue, 16 May 2017 11:40:08 GMT

Are you using SDK 13? What ATT MTU size, and if you can enable DLE depends on what iPad version and what iOS version your iPad has.

If you enable DEBUG logging (#define NRF_LOG_DEFAULT_LEVEL 4 in sdk_config.h), you should be able to see the parameters that is negotiated between the central and peripheral.

RE: How to increase Data Rate

Ferhat B — Tue, 16 May 2017 11:11:07 GMT

Is it acceptable to send 158 byte in pheripheral usage.

RE: How to increase Data Rate

Ferhat B — Tue, 16 May 2017 11:06:17 GMT

I tried to fill 15 packet in other mcu. (every pack has 20 bytes) Thans send one by one every pack, squentaly. (Means 15 times 20 byte sequental) Result better.

But i read Soft Device send 6 packs one time, so i understand problem is not ble waiting.

RE: How to increase Data Rate

Ferhat B — Tue, 16 May 2017 11:01:28 GMT

Does uart interrupt works while sending pack. I read Soft Device dedicated to 20 bytes pack, Can i increase it.

I tried MSEC_TO_UNITS(7.5, UNIT_1_25_MS) but didnt make sense. Its an ECG Graph and for this step we use ipad

RE: How to increase Data Rate

Sigurd — Tue, 16 May 2017 10:42:24 GMT

Hi,

Is it the BLE data rate you want to increase? What are you connecting against? A smartphone?

You can lower the connection interval by changing the MIN_CONN_INTERVAL and MAX_CONN_INTERVAL values. Try setting it to e.g :

#define MIN_CONN_INTERVAL               MSEC_TO_UNITS(7.5, UNIT_1_25_MS) 
#define MAX_CONN_INTERVAL               MSEC_TO_UNITS(20, UNIT_1_25_MS)

There are also several other things you can do to increase the data rate. Such as increasing the ATT MTU size, enable Data length extension (DLE) and enable Connection event length extension.

RE: How to increase Data Rate

Ferhat B — Tue, 16 May 2017 05:45:30 GMT

I made pack length to 20bytes, Can we make uart active while ble send pack. How we make ble send time to 7.5ms