Is there a way to reset the output queue for a QModbusRtuSerialMaster instance.
I think that the other end is being saturated with retries which it can't handle, causing QModbusRtuSerialMaster to retry making the problem worse.
A possible solution would to reset the output queue, removing pending requests, if there is no reply for a particular message after some time.
I've looked through the source code and documentation and I can't see any obvious method.
I would guess simply closing and re-opening it will not flush the queue immediatly and instead wait for the queue to clear.
I don't think you can. Although there might be some workarounds: for example closing the connection or, since the request queue is handled internally, you can reduce the timeout and the number of retries.
Also, I think that if your slave cannot handle the request, you should change your business logic in order to reduce the request or create your own queue and send them with different timings.