Platforms need common symbols for indicating RAM size.

[WestfW]

AVR arduinos define RAMSTART and RAMEND, Due defines IRAM0_SIZE and IRAM0_ADDR, and Zero defines HMCRAMC0_SIZE and HMCRAM0_ADDR. (All via the Atmel include files...)
For the sake of sketches that want to run on all platforms, and want to modify their memory consumption based on how much memory is available (ie in buffers; similar to the way that HarwareSerial sizes the ISR buffers), it would be nice to have common symbols that would allow a programmer to determine memory size. (probably RAMSTART and RAMEND, since they're already in use. I had to dig to find the SAM symbols.)

[sandeepmistry]

@WestfW I've submitted arduino/ArduinoCore-samd#131 to resolve the SAMD side of this.

The SAM core side is going to be a trickier, from the Due product page:

SRAM: 96 KB (two banks: 64KB and 32KB)

So the SRAM does not have continuos addresses:

• IRAM0_ADDR = 0x20000000
• IRAM0_SIZE = 0x10000
• IRAM1_ADDR = 0x20080000
• IRAM1_SIZE = 0x8000

Any thoughts on how to handle the SAM core side? One option is to define RAMSTART and RAMSTART1, etc.