BLE data transfer speed issues with nRF52840

RE: BLE data transfer speed issues with nRF52840

masterLee — Thu, 08 Oct 2020 07:25:14 GMT

Hi,

Yes it makes sense. I will give it a try.

Thank you for your time!

RE: BLE data transfer speed issues with nRF52840

run_ar — Wed, 30 Sep 2020 14:35:07 GMT

Hi,
The gap event length is used by the scheduler. So I think this is limiting the length of the event in this case. This is also used to calculate the number of buffers the sd will allocate up to a maximum of 7. As en alternative you can use sd_ble_opt_set and enable ble_common_opt_conn_evt_ext_t. This will allow the connection event to extend past the allocated time. But I still think you need to increase the length a little to allocate the maximum number of tx buffers.

I the central device can handle a maximum of 6 packets per event the only way to increase the throughput is by using shorter intervals. In addition to the long MTU's and 2mbits. But I don't think that is limited by Android. But might be an issue with certain (older?) chipsets.

RE: BLE data transfer speed issues with nRF52840

masterLee — Wed, 30 Sep 2020 13:45:40 GMT

If I get it right the problem here is that there are no available TX buffers.

So how is this related to the gap event length?

No I have not changed ot, because it is already set to 6 which is the max number I can setsince I use an android central device(smartphone). Right?

But since you mention it again I will try it.

The NRF_SDH_BLE_GATT_MAX_MTU_SIZE is set already to 247

Is there any way that I can make the do{}(while) much faster? I mean the Tx Buffer.

RE: BLE data transfer speed issues with nRF52840

run_ar — Wed, 30 Sep 2020 13:30:05 GMT

Did you try to increase the gap event length?

You could possibly test at the Experimental: ATT_MTU Throughput Example to see how changing various parameters affect the throughput you get.

RE: BLE data transfer speed issues with nRF52840

masterLee — Tue, 29 Sep 2020 10:42:16 GMT

Ok so what can I do to fix it?

RE: BLE data transfer speed issues with nRF52840

run_ar — Tue, 29 Sep 2020 10:14:14 GMT

NRF_ERROR_RESOURCES means there are no available TX buffers. As long as you get that error message, data is not placed in the buffers and transmitted.

RE: BLE data transfer speed issues with nRF52840

masterLee — Mon, 28 Sep 2020 12:55:42 GMT

Thank you for your reply.

In image 1 as you can see, the time that data are being transferred, occupy a very small portion of the entire connection interval(each small pulse represents a transfer). The rest of the connection interval is not used for data transfer as I would expect until the buffer is free again and a new connection interval begins. This takes 90% of the connection interval so the way I see it, it is impossible to achieve higher transfer speed without removing the ( do{}while (err_code == NRF_ERROR_RESOURCES) check.

RE: BLE data transfer speed issues with nRF52840

run_ar — Mon, 28 Sep 2020 12:35:32 GMT

1. There is a limitation to connection event length, set in the sdk_config.h Try increasing NRF_SDH_BLE_GAP_EVENT_LENGTH

2. The NRF_ERROR_RESOURCES error means there are no available tx buffers. If you don't wait for the buffer to be freed before you move on to the next data bulk you will not transfer all the data.

3. You need to optimize the connection settings. More on that in other devzone cases e.g.https://devzone.nordicsemi.com/f/nordic-q-a/62363/nrf52832-throughput-test-with-nordic-uart-service

4. This seems to be enabled by default in sdk 17.0.2. but look at sdk_config.h NRF_SDH_BLE_GATT_MAX_MTU_SIZE and also the defines in ble_nus.c

#define BLE_NUS_MAX_RX_CHAR_LEN        BLE_NUS_MAX_DATA_LEN /**< Maximum length of the RX Characteristic (in bytes). */
#define BLE_NUS_MAX_TX_CHAR_LEN        BLE_NUS_MAX_DATA_LEN /**< Maximum length of the TX Characteristic (in bytes). *

5. 250 kBytes is not possible. Due to protocol timing restrictions and packet overhead the max is about 1.3 mbps. See SD guide on throughput: infocenter.nordicsemi.com/.../ble_data_throughput.html