fix SERIAL_BUFFER_SIZE for SAMD & nRF5x (Adafruit)

[hathach]

This PR fixes current master build with SAMD & Adafruit nRF core. PR #448 introduce the usage of SERIAL_RX_BUFFER_SIZE however this symbol is not define on SAMD & nRF core. There is SERIAL_BUFFER_SIZE that should be used

https://github.com/arduino/ArduinoCore-samd/blob/master/cores/arduino/RingBuffer.h#L31

current build errror

SerialFirmata.cpp: In member function 'void SerialFirmata::checkSerial()':
SerialFirmata.cpp:368:56: error: 'SERIAL_RX_BUFFER_SIZE' was not declared in this scope
           if (!((bytesToRead <= 0 && bytesAvailable >= SERIAL_RX_BUFFER_SIZE/2)
                                                        ^~~~~~~~~~~~~~~~~~~~~
/home/hathach/Arduino/libraries/firmata/utility/SerialFirmata.cpp:368:56: note: suggested alternative: 'SERIAL_BUFFER_SIZE'
           if (!((bytesToRead <= 0 && bytesAvailable >= SERIAL_RX_BUFFER_SIZE/2)
                                                        ^~~~~~~~~~~~~~~~~~~~~
                                                        SERIAL_BUFFER_SIZE
Multiple libraries were found for "Firmata.h"

[zfields]

I would request a nested #if, so it made clear the order of precedence for sourcing SERIAL_RX_BUFFER_SIZE.

// The RX and TX hardware FIFOs of the ESP8266 hold 128 bytes that can be 
// extended using interrupt handlers. The Arduino constants are not available
// for the ESP8266 platform.
#if !defined(SERIAL_RX_BUFFER_SIZE)
  #if defined(UART_TX_FIFO_SIZE)
    #define SERIAL_RX_BUFFER_SIZE UART_TX_FIFO_SIZE
  #elif defined(SERIAL_BUFFER_SIZE) // For SAMD and nRF5x core
    #define SERIAL_RX_BUFFER_SIZE SERIAL_BUFFER_SIZE
  #endif
#endif

This appears to be a good candidate for abstraction with a FIRMATA_SERIAL_RX_BUFFER_SIZE variable. Not to mention, when viewed like this, it illustrates we are not guaranteed to have a default value for SERIAL_RX_BUFFER_SIZE, which can be easily supplied with an #else preprocessor command.

[hathach]

Push to my branch but github doesn't update PR, close & reopen PR as a trick to force update

[zfields]

The code looks good to me!

@soundanalogous has the hardware to run tests before we merge, so I'll let him work his magic.

Thanks for the PR!

[hathach]

with the removal of FIRMATA_SERIAL_RX_DELAY for SAMD at commit 6e6b5c8

This PR may not be needed anymore. I am not sure the above commit an interim commit or not. Feel free to merge or close this issue or tell me if you need to make any changes.

[soundanalogous]

6e6b5c8 fixes the compile issue but doesn't enable support for using a serial buffer with SMAD boards.

I'll look into getting this merged sometime this weekend if I can find some time to test it.

[hathach]

thanks, feel free to merge whenever you have time.