CC2650MODA: Bluetooth hangs when sending data too fast - SPP server example

Hi Zahid,

I was trying to send a ton of bytes - I will describe better bellow but better what I found to be the problem:

I found the problem to be related to the SDI/UART buffer was 128bytes and the queue message had also that size (the SDItask to applicationTask queue).

In the application task, it tried to straight up put all the data to send in the "bluetooth hands" (using SerialPortService_SetParameter). This would return a error MSG_BUFFER_NOT_AVAIL when the data was over the MTU-3 (or was it -4?) which is hardcoded at 65. Since there was no success, the UART message would not be discarded and there would be an attempt to send it again - this of course resulted in continuous failing.

The LED blinking with a delay should not by itself influence the system to cause this behavior.

I had a test where some bytes we're sent without issue and then after some time, 200 bytes we're sent at max speed.  This would cause 2 messages queues to be sent with a length of 128 and 72. The first one with 128 bytes would trigger this problem right away.

I changed the PDU to 255 in both client CC2650 and server C2650 and the issue was gone.

I strongly suggest this example to be revised. The application should instead of sending the message queue straight up to SerialPortService_SetParameter, it should break it into smaller chunks with max size of the MTU (again for me it had to be PDU-4-3 or MTU-3 for some reason). I found another bug too. I might attempt, if I have time, to make a commit (that's the correct term?) to the github - though I never really done that - with my suggestion.

Another thing, might it not be best to have the MTU to be just 20? These will surely be used with android, and most apps will not handshake the MTU and keep the default value of 20 without the CC2650 server knowing. (just a thought).

Here is what I did (for packages with max sizeof 20) to make everything work:

                    uint16_t l = pMsg->length;
                    uint8_t *a = pMsg->data;
                    //send in packets of 20 bytes
                    while(l > 20){
                        retVal = SerialPortService_SetParameter(SERIALPORTSERVICE_CHAR_DATA, 20, a);
                        l -= 20;
                        a+=20;
                    }
                    //send the rest of the bytes
                    if(l != 0)
                        retVal = SerialPortService_SetParameter(SERIALPORTSERVICE_CHAR_DATA, l, a);

Can you please verify if I will not have issues by calling SerialPortService_SetParameter in a row? As far as I can see the data to be sent reaches the bluetooth task through a queue - so there won't be any problem of sending more data into bluetooth task before the previous one is transmited, right?