[Tinyos-devel] Proposed UART Changes

[Trevor Pace]

I am currently working as a research assistant for Dalhousie University and
I have been given the task of interfacing a Glucose Meter with a Crossbow
Iris mote. I have written private modules that request and process data
using the UART0 module on the Iris Atmega128 processor. However, I ran into
a few issues with UART and TinyOS.

FIRST:

The Glucose Meter communicates at 9600 baud however the default baud rate
for the iris mote is defined in /platforms/micaz/hardware.h as such:

enum {
  PLATFORM_BAUDRATE = 57600L
};

This means that in order for me to use a different baud rate I must change
that to 9600L, which is not good. My proposed solution to this (that I am
currently using) is to use pre-compiler defines:

#ifndef PLATFORM_BAUDRATE
#define PLATFORM_BAUDRATE 57600L
#endif

That allows me to just add to my makefile:

CFLAGS += -DPLATFORM_BAUDRATE=9600

And sure enough it works for that program only, as it should.

SECOND:

The way the glucose meter is setup it is only possible to do Half-duplex
communication, and whatever I transmit using UartByte.send() will be
received; throwing the event UartStream.receivedByte(). This means that I
must disable reception for the UART module (not just interrupts because the
module will still be buffering the received data). However, there exists no
command to disable/enable either the receive or transmit modules at the
PlatformSerialC abstraction (which provides common interfaces to all types
of motes supporting UART communication).

My solution for this was to write a function to disable reception and then
send a byte, though this only will work for ATM128 processors:

CLR_BIT(UCSR0B, 4);
call UartByte.send(byte);
SET_BIT(UCSR0B, 4);

My proposed solution for this is to create a new interface called
UartControl which provides at least the following commands:

command void disableRx();
command void enableRx();
command void disableTx();
command void enableTx();

They could of course return errors if need be. This interfaces would be
provided from the HPL abstraction to the PlatformSerialC module which would
then pass it on. Thus providing the ability to disable/enable reception or
transmission of the UART module.

I am just wondering whether this is an area you feel that TinyOS should move
towards. Surely there are other devices which may want to communicate using
serial communication so these ideas won't apply to just my own situation. If
you feel that this is something you would like to see I would be more than
willing to write the code to implement this.

Trevor Pace
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