[Tinyos-help] Help writing to telosb over UART in Python

[Darren Bishop]

I am writing a Pyhton software to manage our mote testbed; I must use Python 
to integrate into the 'larger' system and I must use TinyOS-1.x.

I am having trouble writing to the motes over UART. I can read from them 
perfectly i.e. I have implemented the HDLC-like framing and CRC calculation 
and all is well. For example, I read the following from a telosb mote running 
the Oscilloscope image:
rxpkt: 7e 42 0e 00 00 00 00 00 7d 5e 00 1b 7d 5d 00 00 8d 00 00 0d 9c dc 43 01 
00 f6 00 08 66 3f 7e

[As an aisde, can anyone explain why the payload length is moved to rxpkt[2], 
and where bytes rxpkt[3-7] come from?]

My goal here is to implement a 'command interpreter' on the mote, where 
commands are sent from the PC.

The content of CommandMsg.h is as follows:

enum {
	COMMAND = 1 << 15,
	STATUS = 0 << 15,
	INTERNAL = 1 << 14,
	EXTERNAL = 0 << 14
};

struct CommandMsg
{
    uint16_t cmd;
    uint16_t mask;
    uint16_t arg;
};

enum {
	AM_COMMANDMSG = 20
};

The byte array (Python: array.array('B')) of data I want to send goes through 
the following transformations:

Data: 0b 00 00 00 a3 08 (11, 0, 2211)
Message: 7e 00 1b 7d 0b 00 00 00 a3 08
Packet: 7e 42 06 00 00 00 00 00 7d 5e 00 14 7d 5d 0b 00 00 00 a3 08 f9 f0 7e

The final packet format reflects what I read of the wire i.e. Packet[2] is the 
data length followed by 5 pad bytes.

I open the port with the following Python code (assume necessary modules are 
imported):

def open(self):
	self.__fd = os.open(self.__port, os.O_RDWR|os.O_NOCTTY)
        iflag, oflag, cflag, lflag, ispeed, ospeed, cc = \
	termios.tcgetattr(self.__fd)
        cflag = termios.CS8 | termios.CLOCAL | termios.CREAD
        iflag = termios.IGNPAR | termios.IGNBRK
        oflag = 0 # saw this in serialsource.c
        ispeed = termios.__dict__['B'+str(self.__baudrate)]
        ospeed = termios.__dict__['B'+str(self.__baudrate)]

        termios.tcflush(self.__fd, termios.TCIFLUSH);
        termios.tcsetattr(self.__fd, termios.TCSANOW, \
	[iflag, oflag, cflag,  lflag, ispeed, ospeed, cc]);


When I write the packet, the little green LED by the mote-USB connector (not 
the main 3-LEDS) flashes, but I do not get the desired result i.e. the main 
red-LED does not switch on (as it is 'commanded' to).

Has anyone achieved writing to a (telosb?) mote in C or Python? Have I set the 
wrong output flags (oflag) on the serial port maybe? Have I got the frame 
format wrong?

Your help is appreciated.

-- 
Warm regards,

Darren Bishop, MSc, BSc (Hons), MBCS