Re: LCD Support in kernel

From: Tim Pushor (timp_at_crossthread.com)
Date: 09/16/04

  • Next message: Scott Gerhardt: "Re: What to backup" 
    Date: Wed, 15 Sep 2004 16:21:48 -0600
To: Henrik W Lund <henrik.w.lund@broadpark.no>

    Henrik W Lund wrote:

    >>
    >> I am planning on purchasing a crystalfontz LCD panel to be able to
    >> have a rudimentary interface with the system without having a
    >> keyboard/monitor/shell.
    >>
    >> I'm not sure whether to go the serial or USB route. What I want to do
    >> is to be able to display status as the system is coming up, then have
    >> a user level application accept input from the panel and display
    >> various statistics, then when the system is brought down, for the
    >> panel to notify the user that it is safe to turn off the machine.
    >>
    >> For the startup and shutdown I would need to hack stuff into the
    >> kernel. I have done a fair bit of C programming over the years, but
    >> never worked in the kernel. So I have 2 real questions:
    >>
    >> Would it be easier to control the USB or Serial panel from the Kernel?
    >> And - does anyone have any recommendations as to where I could even
    >> start looking in the kernel to do what I want?
    >>
    >> Thanks,
    >> Tim
    >>
    >> (Please CC: me as I am not subscribed to this list - Thanks!)
    >
    >
    > Greetings!
    >
    > I'd guess that the serial version would be the way to go, since
    > FreeBSD has builtin support for displaying to serial console
    > (typically used for headless systems, allowing admins to use a serial
    > communications program like HyperTerminal under Windows for out- and
    > input). This is, of course, assuming that the LCD panel interfaces
    > like a serial terminal. If it does, you've got about half the job
    > done, as FreeBSD will happily print bootup and shutdown information
    > out-of-the-box.
    >
    Well, I was *hoping* to be able to display my own messages to the
    display. I suppose I should have explained a little better - the display
    is a 2 line x 16 character display, so the output from the kernel
    startup would probably just be a blur ;-) It may even be difficult to
    determine where it is hanging if it were to hang (due to the small size
    and information capacity).

    > Further, if it announces touches to the screen as regular keypresses,
    > you're even luckier. All that really would remain for you to do was to
    > write the UI (as I don't think a ready-made solution exists for what
    > you want. I may be wrong, though). If this is to be a GUI (on top of
    > X, that is), you'd have to find out if X will display to serial
    > terminal. If it doesn't, I'm sure any idea you can come up with is
    > just as good/better than mine. ;-)
    >
    The display actually fits iniside a 5 1/4" drive bay, and the
    pushbuttons do not emulate a keyboard. I am not to worried about it,
    however, as I don't really need to be able to read the keypad during the
    startup and shutdown process.

    > Worst case scenario; the LCD screen interfaces like a toaster. My best
    > bet would be to do a kernel module. More info on how to do those can
    > be found here:
    >
    > http://www.freebsd.org/doc/en_US.ISO8859-1/books/arch-handbook/index.html
    >
    Thanks for the link - I will be sure to go through everything there. I
    *have* written device drivers for other operating systems and done a
    fair bit of interface code in C in the past.

    If it is possible, I would prefer to use the USB model, but that would
    require me homehow figuring out how to use the device drivers from my
    kernel module. A cursory look through the Architecture Handbook doesn't
    cover that (the USB device driver for the lcd panel in question already
    does exist in FreeBSD).

    I would also have to make sure that the USB subsystem (and probably the
    serial devices as AFAICT the USB driver for the lcd looks like a serial
    port to applications) was loaded as early on as I could so I could use
    it for most of the FreeBSD startup - and what about the shutdown? Will
    the device exist and work when the kernel is in the 'halted' state?

    I have thought about the possibility of talking directly to the serial
    port (I have done 16*50 interface code before) during my serial module,
    but that may open another can of worms.

    > I encourage others to elaborate (and correct me, of course) as they
    > see fit. Not having done much actual work on FreeBSD myself, what I
    > propose here is what my programmer's mind sees as probable based on
    > what documentation and experimenting I have seen and done.

    Thanks Henrik, I apprecate the response ;-)

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