Soft Device received data handling

Question

Hi, 
 I am having some issues transferring data from an iPhone to the nRF51822.
Actually, I write block of 16 of my data from the iPhone on a specific characteristic on the nRF51822 and on each write event, I transfer the written data to another microcontroller which handles it.
When dealing with "huge" amounts of data (around 5kB), it happens sometimes that the data rate slows down drastically (like 4kB/s to a few bytes per second) and I receive the error on the iPhone that some blocks could not be written. 
 As I haven't clearly identified the issue yet, I would like to know more about how the soft device handles the data written on a characteristic (to give me a hint to debug properly). Is it cached while not handled by the on_write event? What are the buffer sizes?...

Matthieu Tardivon · Accepted Answer

Self answer but can be useful for the community. 
 I limited the amount of data sent by the iPhone to 1kB and wait for the nRF51822 to ask for the following block and it worked better as I didn't lose data anymore.
However, the data rate was fine at the beginning and dropped drastically during the transfer. The reason for that was that the connection parameters were not complying with the iOS requirements. Thus the iPhone was asking for a connection parameter update, which screwed the whole thing up. Once the connection parameters corrected on the nRF51822, it works nicely.

Soft Device received data handling

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