[Tinyos-devel] Proposed UART Changes

[Philip Levis]

On Jun 17, 2009, at 12:56 PM, Trevor Pace wrote:

> Hey Eric,
>
> The problem I am seeing right now is that I am developing a module  
> which should in theory work on any mote that supports UART. However,  
> there exists no hardware abstraction interface provided by all  
> platforms that would allow me to disable/enable communication.  It  
> does exist at the lower HPL but that is implemented per chip.
>
> So for me to shut-off my reception temporary I must wire a chip- 
> specific HPL Uart module removing the possibility of compatibility  
> with other chip sets. The Msp430HplUart you mentioned does support  
> enabling/disabling for sure, unfortunately by the time it gets to  
> the PlatformSerialC abstraction (which is available to all chipsets  
> with UART) then I lose that ability.

It seems we definitely want a UartControl or UartSettings interface.

One constraint is that we want to catch bad settings at compile-time.  
For example, trying to set the UART to a speed the MCU does not  
support should be a compile-time error. The standard way to do this is  
with enums: if you use an undefined enum you don't compile.

How about something like

interface UartControl {
   command error_t enableRx();
   command error_t disableRx();
   command bool rxEnabled();

   command error_t enableTx();
   command error_t disableTx();
   command bool txEnabled();

   // TOS_UART_2400, TOS_UART_57600, etc.
   command error_t setSpeed(uart_speed_t spd);
   command uart_speed_t speed();

   // TOS_PARITY_NONE, TOS_PARITY_EVEN, TOS_PARITY_ODD, etc.
   command error_t setParity(uart_parity_t par);
   command uart_parity_t parity();

   command error_t setStop();
   command error_t setNoStop();
   command bool stopBits();
}

Thoughts?

Phil