[lcd4linux] lcd4linux design ideas

[Michael R. <re...@eu...>]

Hi lcd4linux-users,

I want to give you some feedback about what has happened in my brain the 
past days...


As some of you might know, I got two really cool displays from 
MatrixOrbital. They have features that lcd4linux does not support at the 
moment, so I tried to implement them:

- Keypad support
- temperature sensors
- Fan RPM measurement
- Fan PWM control

You could dividethem into two parts: input functions (keypad, sensors) 
and output functions. I decided to work on the output first.

The Fan PWM control acts like a normal GPO (which would be supported by 
lcd4linux), but it's not a 'digital' one (which could be switched on or 
of), but an analog one, which can have values from 0 (switched off) to 
255 (full power). There's no support for such an analog GPO in 
lcd4linux. I started to modify this.

Then I realized that building a value for such a GPO isn't that easy. 
Think of a combination of one or more temperature sensors, and the fan 
RPM control. How would you configure this?

The best way would be the possibility to specify an algebraic 
expression, like

fan1 = 1000+150*log(30+0.25*temp2) + 250*(25+0.18*temp3)

such expressions would be cool with 'normal' GPO's, too. Now you can 
configure a GPO to be sensitive to any token, e.g. 'disk write:

GPO1 %dw

It would be activated whenever one single bit would go to the disk

better would be

GPO1 %dw>1000
or
GPO1 %dw>%dr

or anything you could think of...


Then I found a little piece of code, called the "Expression Evaluator" 
by Mark Morley, and found this a very small and simple solution for my 
issues. The code supports 'normal' algebraic expressions (2+3), variable 
assignments (a=3; b=5; c=2*a+b), functions (sin(25*b), and can be easily 
extended or new functions added.

To those concerned about size: It's really small, believe me! I cannot 
tell you exactly at the moment (as it does not compile), but I got an 
earlier version compiled and linked as a simple example, which has 10k.


I already extended the code to support 'logical' expressions (a>5,
b>10 & (c | d<100), and at the moment I'm implementing 'string' functions.


As the code is that simple, and new functions can be easily registered, 
I thought this could be the basis for a redesign of some lcd4linux 
internals:

Clients: Every client registers one or more new functions, and handles 
these functions with parameters:

e.g. net(interface, direction) could be: net('*', 'r') or net('eth1', 'rw')

So the long-wished 'statistices for each lan interface' could be solved 
this way


One could do calculations with these functions:

If you prefer PPP throughput in bytes/sec, you use ppp(0, r)
If you prefer kB/sec, use ppp(0,r)/1024
If you prefer MB/h, use ppp(0,r)/1024/1024*3600

other advantage: the 'temp1.factor' and 'temp1.offset' would be obsolete...

There would be a 'transform' function, where you could specify the field 
width and number of decimals, which is fixed now. Maybe like C printf(), 
maybe like dBase ('####.##')


The layout config scheme would stay as it is, but would support such 
expressions, too.


Code is not in the CVS by now, because it doesn't even compile. But this 
will change really quick...


What do you think about this? Have you got any other ideas what we could 
solve with this method? Do you think this is a good idea?


All comments are welcome!


bye, Michael

-- 
netWorks                                          Vox: +43 316  698260
Michael Reinelt                                   Fax: +43 316  692343
Geisslergasse 4                                   GSM: +43 676 3079941
A-8045 Graz, Austria                          e-mail: re...@eu...