is there a problem on this simple code

[jrlen balane]

the assembly program for the microcontroller is created by a
classmate. he based the protocol for the serial program from a
protocol he found in the internet. unfortunately, i can't find the
fpdf file, guess i'll just ask him later when he comes back.

On 13 Mar 2005 03:28:43 -0800, John Machin <sjmachin at lexicon.net> wrote:
> 
> jrlen balane wrote:
> > the hardware is a school project that uses a microcontroller for
> "light dimming"
> > the message command "67" will tell the microcontroller (PIC16F877) to
> > do a command (to control the intensity of a lamp)
> > the message command "70" should tell the GUI that the microcontroller
> > has started transmitting.
> > the message sent by the GUI is different from the message sent by the
> > microcontroller
> > (but i guess sir John is right, i think i should use different
> > variable for the data transmitted and data received)
> > i am currently developing this part of the project which implements
> > the serial communication
> > i've fixed the command and total_data since i know beforehand that
> > this will be its value.
> > to simplify the program, i have also fixed the message_no since the
> > microcontroller will still accept the transmitted data as long as the
> > checksum == 0.
> 
> (1) But it's NOT zero after the first time around! (2) How do you know
> what it will accept? Guessing or reading the manual? If the checksum is
> not zero, then what happens? Please quote the exact section from the
> manual.
> 
> >
> > anymore suggestion???...
> 
> YES: show the whole program; you have left out the initialisation part.
> 
> > ==================================================
> > command = 67
> > message_no = 1
> > total_data = 2
> > item=10000
> > for item in range(10000, 30001, 250):
> >     ser.open()
> >     data_hi, data_lo = divmod(item, 0x100)
> >     checksum = -(data_hi + data_lo + 0x46) & 0xff
> >     ser.write(pack('6B', command, message_no, total_data, data_lo,
> > data_hi, checksum))
> >     data = ser.read(10)
> >     (command, msg_no, no_databyte, temp1, temp2, pyra1, pyra2,
> > voltage, current, checksum) = unpack('10B', data)  #serial receive
> > protocol
> >     print command, msg_no, no_databyte, temp1, temp2, pyra1, pyra2,
> > voltage, current, checksum
> >     ser.flushInput()
> >     ser.close()
> >
> > ===================================
> > i've rewritten the code and deleted some unnecessary entries, now the
> > problem is :
> > 21 6 64 64 192 0 0 0 175 70
> > 70 2 6 64 64 192 0 0 0 114
> > 70 11 6 64 64 192 0 0 0 105
> > 0 0 104 70 2 6 64 64 192 0
> > 70 2 6 64 64 192 0 0 0 114
> > 128 128 103 70 2 6 64 64 192 0
> > 70 2 6 64 64 192 0 0 0 114
> > 16 208 246 70 2 6 64 64 192 0
> > 70 2 6 64 64 192 0 0 0 114
> >
> > ===================================
> > the received data does not always start with the command "70",
> > is this ok??? since i can always search first for the command "70"
> > before i read the remaining 9 bytes, then calculate first for the
> > checksum before finally accepting the received data.
> >
> > am i making sense here?! please help me...
> 
> As Dennis has told you, searching is pointless. You are losing data
> now. Before you weren't losing data. Until you fix that problem,
> fiddling with anything else is pointless. You have stopped doing
> sleep() -- why? You are now doing ser.open() and ser.flushInput() and
> ser.close() on *each* time around the loop -- why? I'd strongly suggest
> you put these back the way they were. THEN do what I told you to do:
> use a separate tx_command and rx_command. The first time through the
> loop, command is set to 70 from the received data, and then the second
> time around, you SEND 70, not 67!!! Fix that, and then show us what you
> get. DON'T try searching for a 70. Don't thrash around trying multiple
> changes at once -- make changes one at a time so you can see the
> effects.
> 
> Do you have a part number for the manual which describes the 67 and 70
> "commands" and the check-sum? Is the manual on the internet anywhere?
> 
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