Serial store & forward

[jnsbyr]

Activating a host stream write buffer (see #447) may result in unexpected behaviour: when receiving serial data with e.g. 9600 baud it may happen that without write buffers several received serial bytes where sent to the host in the same TCP frame but with write buffers each byte gets sent separately again, so nothing is gained.

The reason for this is quite simple: the host stream write buffer increases the Firmata performance and now the serial port can be polled faster than bytes are received. Even without a host stream write buffer this will happen anyway at lower baud rates.

This kind of fragmentation can be avoided by implementing a store & forward buffer for the incoming serial data. It can be globally activated and configured by defining an acceptable forwarding delay with

#define FIRMATA_SERIAL_RX_DELAY 50

in SerialFirmata.h.