is there a problem on this simple code

jrlen balane nbbalane at gmail.com
Tue Mar 15 01:15:22 CET 2005


@sir John
could you please show me how to do this exactly? it's in the "tip of
my toungue" but i just can get it, please...


On 14 Mar 2005 14:06:15 -0800, John Machin <sjmachin at lexicon.net> wrote:
> 
> jrlen balane wrote:
> > why is it that here:
> >
> > 1)rx_data = ser.read(10)
> >     (rx_command, rx_msg_no, rx_no_databyte, temp1, temp2, pyra1,
> > pyra2, voltage, current, rx_checksum) = unpack('10B', rx_data)
> >     print rx_command, rx_msg_no, rx_no_databyte, temp1, temp2, pyra1,
> > pyra2, voltage, current, rx_checksum
> >
> > >>> type (rx_command)
> > <type 'int'>
> >
> > but here:
> >
> > 2)rx_data_command = ser.read()
> 
> Are you sure you have really have read() -- which will read all
> available data -- or read(1) -- which will read just one byte???
> 
> >     (rx_command) = unpack('1B', rx_data_command)
> >
> > >>> type (rx_command)
> > <type 'tuple'>
> >
> > how can i make rx_command of type 'int' if i am to use 2)?
> 
> unpack returns a tuple. In 1) you unpack it. In 2) you don't unpack it.
> 
> either do this:
> 
> (rx_command,) = unpack('1B', rx_data_command) # unpack tuple
> 
> or this:
> 
> rx_command = unpack('1B', rx_data_command)[0] # grab 1st element of
> tuple
> 
> or, simply, to get what you want, just do this:
> 
> rx_command = ord(ser.read(1))
> 
> >
> > @sir John
> > the reason why my first post all starts with '70' , which is what i
> > really wanted to happen, is that it is buffered. the microcontroller
> > sends data at a very fast rate, that the program just retrieve data
> > from the buffer. so basically, they are not "real time". but there
> are
> > also cases where the command is in other position. the good thing is,
> > it remains in that position throughout...
> 
> It wasn't doing that before; In the second posting with examples, there
> were some that were a MIXTURE of (a) 70 as the first byte of 10 (b) 70
> as the fourth byte of 10 (128 128 103 70 2 6 64 64 192 0)
> 
> >
> > i want to make the program show data in "real time" so everytime i am
> > able to read data, i immediately use flushInput(), to erase data from
> > the buffer.
> 
> How large is the buffer?
> 
> >
> > so i what i want to do now is to search for the rx_command first
> > ('70') just so i know where my data should start.
> 
> OK, so NOW you are saying that the microcontroller is pumping out data
> continuously, it's not one response to each of your "67" commands???
> 
> In that case what I'd suggest you do is to read 19 bytes from the
> serial port (with time-out, I'd suggest; give up if you don't get 19
> bytes returned), and for each k in range(9), test for:
> 
> (a) byte[k] == 70
> (b) byte[k+2] == 6
> (c) checksum(byte[k:k+10]) == 0
> 
> If you don't get a valid data packet, give up.
> 
> This should snatch one valid data packet (if there are any) from the
> torrent.
> 
> --
> http://mail.python.org/mailman/listinfo/python-list
>



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