Getting BLE_HS_ENOMEM errors when sending data in loop about nimble-arduino HOT 4 OPEN

Some logs would help but I suspect that the delay is a bit too short, do you know what the connection interval is?

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The connection interval (desc->conn_itvl) is 24 units, which I believe is 30 msecs. Does that mean I should make my delay between notify's a bit over 30 msecs to avoid using up all the buffer? Is there a way to force a more frequent connection interval?

from nimble-arduino.

I added a print to the onStatus callback. It looks like the first 8 notify's are okay but it starts to fail after that:

onStatus TX status: 1 rc: 0
onStatus TX status: 1 rc: 0
onStatus TX status: 1 rc: 0
onStatus TX status: 1 rc: 0
onStatus TX status: 1 rc: 0
onStatus TX status: 1 rc: 0
onStatus TX status: 1 rc: 0
onStatus TX status: 1 rc: 0
onStatus TX status: 4 rc: 6
onStatus TX status: 4 rc: 6
onStatus TX status: 4 rc: 6
onStatus TX status: 4 rc: 6
...

I increased the delay to a full second (1000 msecs) and it still sends only the first eight.

from nimble-arduino.

I found my problem.

I was calling writeTest() in response to a request coming from the client. Thus, it was called from the onWrite() callback in my subclass of BLECharacteristicCallbacks. I'm guessing that the BLE stack holds a lock until the onWrite() callback returned. Thus, NimBLE was queuing notify messages to be sent when onWrite() returned, but when writeTest() did too many notify() calls it ran out of buffers.

The fix was to have onWrite() set a flag to request that writeTest() be called from the loop() function. With that change, writeTest() can send thousands of bytes. I'm seeing throughputs of about 5k bytes/second from a micro:bit V2 to my MacBook Pro, which is great!

I now have a new problem.

I'm using a delay in the writeTest() loop to avoid queuing data faster than NimBLE can send it. To maximize bandwidth, I want to minimize that delay. Through trial-and-error, I've found that 12 msecs works but 10 msecs results in errors (status: 4, return code: 6) and lost data. I'd rather not depend on a delay for this.

Is there a function I can call to be sure that a buffer is available for doing a setValue and notify on an attribute? Alternatively, is there some way to get an immediate return code indicating that the setValue or notify failed and should be tried again later? (I'm using onStatus now, but I'm not sure exactly when that gets called. Is it triggered by the setValue() or the notify() call? Is onStatus() called immediately when the error occurs?

Thanks!

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