BLE Reads of 500 bytes taking 9 seconds

RE: BLE Reads of 500 bytes taking 9 seconds

SleepingDog — Mon, 03 Feb 2020 12:53:21 GMT

Thank you *VERY* much, Dmitry. That was it. Clearly I have more learning to do with respect to BLE. I did not understand this aspect of the protocol at all.

RE: BLE Reads of 500 bytes taking 9 seconds

Sigurd — Mon, 03 Feb 2020 10:09:06 GMT

Decreasing the connection interval will help. I also recommend increasing NRF_SDH_BLE_GAP_EVENT_LENGTH in sdk_config.h from 6 to e.g. 320

RE: BLE Reads of 500 bytes taking 9 seconds

Dmitry — Sun, 02 Feb 2020 19:26:58 GMT

Hi,

The connection interval in original example is 100-200 msec. If you didn't change it, device can transfer 5-10 packets per second. A default MTU size is 23 bytes that allows you to transfer your characteristic by twenty five 20-byte chunks, requiring 50 packets - 25 requests and 25 responses, so total time will vary from 5 to 10 seconds - that's your case. To improve speed, a simplest way is to decrease connection interval:

#define MIN_CONN_INTERVAL      MSEC_TO_UNITS(15, UNIT_1_25_MS)
#define MAX_CONN_INTERVAL      MSEC_TO_UNITS(20, UNIT_1_25_MS)

A better speed improvement can be achieved by increasing MTU up to 251 bytes and use DLE (data length extension), but it has to be supported by both sides. You can search forum, there was a number of threads about increasing MTU size.