Reducing latency - BLE nano as MIDI controller

[Pasquale]

Hi All, I am building a wireless MIDI controller using the BLE nano v2.0 from RedBearLab. MIDI is a protocol to control software musical instrument, therefore latency needs to be <10ms and at the moment it ranges roughly between 20 and 100ms.

I am using UART service to send data between the BLE peripheral and the central device (my laptop). The way I test the latency is by sending a single number or character from the ble module (using the serial monitor) to a connection utility using UART (I am using the Bluefruit Connect from Adafruit).

I use Arduino IDE to upload the firmware on the board and I have already tried to decrease the connection interval to reduce the latency. It has improved with this modification, but is not short enough yet.

#define MIN_CONN_INTERVAL MSEC_TO_UNITS(1, UNIT_1_25_MS)
#define MAX_CONN_INTERVAL MSEC_TO_UNITS(1, UNIT_1_25_MS)

static Gap::ConnectionParams_t conn_params = {
  .minConnectionInterval = MIN_CONN_INTERVAL,
  .maxConnectionInterval = MAX_CONN_INTERVAL,
  .slaveLatency = 0,
  .connectionSupervisionTimeout = 10000
};

I noticed that sometimes the latency is short and sometimes is longer and that makes me assume there is a sort of period which controls how often packets gets sent, but I am not totally sure.

Do you know what other parameters or settings I can change in order to solve the issue?

I want to point out that I have already done this with the Adafruit Feather 32u4 with very short latency, therefore is definitively possible, but I need to use a smaller board.

Thanks in advance for any help!

[Pasquale]

Thanks for the comment.

I am using a MacBook Pro as a central device and the latency ranges between 30 and 100 ms, it varies. It is true that the UART service is slower but I have achieved better performances with another board (with its own firmware) and works better that the BLE Nano. However, I need to use the Nano for dimensions.

Are there other parameters I can play with to increase the Throughput of the UART service.

Also, does any body know how to implement the MIDI service on the BLE Nano?

Thanks

[MartinBL]

Was the other board also using a proprietary BLE service? Or was it using the actual MIDI service? As mentioned, this might make a big difference.

[Pasquale]

The other Board was a Feather 32u4 and was always using UART service with it.

[MartinBL]

Are you using the same code on the Nano and Bluefruit?

[Pasquale]

The code is different, because Adafruit has developed its own libraries to work with ble.

For example, to send a message through UART with the feather, you just need to use:

ble.print("message")

with the Nano everything is a bit more complicated. I am linking the complete code I am using just to test the UART service latency.

Code

Thanks for any insight.