[Lcd4linux-devel] Fwd: Re: [lcd4linux] uClinux patch.

[Hans E. <ha...@ru...>]

tisdag 16 januari 2007 21:25 skrev du:
> Hi Hans,

Hello Michael.

> I hope you don't mind the CC'ing to lcd4linux-devel....

No problem. Maybe you can create a task in the seemingly smooth Trac system,
we are currently looking at moving over our open parts of our embedded
project to Trac. Looks promising.

> > Meaning we would really want a simple button/LCD interface for an
> > operator to handle, something very simple and easy to set up and use.
> > Ideas involving menu hierarchy in a XML or XML-like format for example(or
> > something very more light weight, a simple intentaion format may do
> > well). Would it be possible/suitable to add such functionality to
> > lcd4linux?
>
> Oh, I read the evil word "Buttons" here :-)
>
> > Saw there was a
> > button plug-in for example. Im more of a hardware/kernel guy than
> > userland/sysadmin so im not well oriented in all the aspects of user
> > interaction in uclinux, maybe/probably this has been done before. Any
> > ideas?
>
> Well, I am thinking about Buttons/keypads for years now. As I'm thinking
> about dynamic layouts....

Yes, UIs or GUIs are allways a hazzle. Im still hesitating to make a
 descition about the LCD/button or touchscreen or whatever will suit our
 project. Hope i can postpone this decision a few more weeks until i know
 what is the right(meaning flexible, not painting ourselves into a crorner)
 solution. Need to investigate more here. Anyone with ideas around this are
 very welcome to speak.

> > I should have checked out the SVN version instead, but no problem of
> > making a new patch since it was no major changes. In short i just wanted
> > to achieve a compile with no referencs to parport related functions,
> > there were a few references to it in drv_HD44780.c/.h even though not
> > allways needed when display sits on i2c (or maybe other hardware as
> > well).
>
> I will provide a special configure target "--with-drivers=HD44780-I2C"
> which will compile the HD44780 driver withaout any parport references.
> Please test & give feedback!

Great, i will try it. Will grab latest SVN whenever you have anything
compiling.

> > And i also needed to
> > change fork() to vfork() since uClinux does not support fork().
>
> erm... are you really sure? From what I know, vfork just saves a few
> cycles if fork() is immediately followed by exec(), but the caller
> blocks until the exec() is successful (so it's dangerous because if
> exec() fails, the behaviour is undefined)

Both are right. UClinux are Linux for MMU-less systems, hence it lacks the
true memory protection and also the complete VM subsystem that Linux
supports - there is NO virtual memory in uclinux and fork() works need
virtual memory to work. fork() create a parent and a child with separate taks
control structures and programs will reside in separate virtual memory
mappings(sharing memory until COW). For details, have a look here:

http://docs.blackfin.uclinux.org/doku.php?id=living_without_forks&s=vfork

> is there any *reliable* preporcessor constant I could use?

Use #ifdef UCLINUX
is the commony used macro whever doing special cases for uClinux, it should
allways be defined when compiling towards uclinux.

> > I think embedded linux is comming strong
> > now so it would be cool for lcd4linux to be the lcd software of choice
> > such systems.
>
> 1000% agree :-)

Great!

> bye, Michael

Adios!

/Hans

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