Updated/added config options for all Due Serial

[bluesign2k]

For USART based Serial (Serial1, Serial2, Serail3), expanded config
options to include 1.5 stop bits and mark & space parity modes. Also
added defines ready for 9-bit implementation - currently commented out
until serial read/write supports it.

For UART based Serial, added ability to set config. Due to UART module
limitations, mode is fixed with 8-bit, 1 stop but parity is selectable
(none, odd, even, mark, space).

In both classes, user configs are masked to prevent bad mode
configuration.

[cmaglie]

@bluesign2k
AFAIR only 8 bit data modes are supported in hardware, currently the compiler doesn't show any error and users may be a bit puzzled why the serial ports doesn't behave as expected (until they look at the documentation of course).

Is there a way to place static assertions to prevent users from doing:

Serial.begin(9600, SERIAL_7N1);

?

[matthijskooijman]

Not sure if that's possible. You could of course not define SERIAL_7N1, though that doesn't give a very clear error message...

C++11 has static_assert, but I think that's only useful for actual constant expressions, not for expressions that might also be variable.

[bluesign2k]

To be honest, I was aware of this issue and did have a look at the possibility of getting the compiler to throw some sort of error if the user tried to set an invalid mode. However, I never managed to find a suitable solution. I debated making the options some sort of child of the class, so the user would have to do something along the line of:

Serial.begin(9600, Serial.SERIAL_8N1);

and therefore the following would throw an error as SERIAL_7N1 isn't a child of Serial:

Serial.begin(9600, Serial.SERIAL_7N1);

...but it seemed messy.

Truth be told, I figured it either would be a problem as users could read the documentation, or someone with better knowledge might have a solution.

[cmaglie]

What about:

#define SERIAL_8N1 UART_Modes.SERIAL_8N1
[....]
#define SERIAL_7N1 USART_Modes.SERIAL_7N1

where USART_Modes is a child class of UART_Modes?

[cmaglie]

Thanks!