Re: [Lcd4linux-devel] RE: [lcd4linux] problem with i2c connected LCD display

[paul k. <pau...@xs...>]

Hi there,

Thanks for inviting me in! I already gave the 0.10 source code a quick 
look (just a download from the sources on the website, no CVS access yet)
Compiles nicely for me, so no problem there.

I agree with Luis his code, it looks nice and usable. But it doesn't 
compile :'(
I spend some time looking for a solution on the internet, and it is a 
bit of a horror story.

First Luis, did you ever get this code working? Right now I assume it 
could have worked with a 2.4.x kernel.

The thing is, the kernel team decided that user space (application) 
access to /dev/.. should not be done. For that reason most kernel 
includes are no longer available. Only exception the i2c includes. 
<linux/i2c.h> etc, but including them results in compile errors. (As 
Michael noted)
The reason is an undefined __user__  macro. Which  is part  of the 
kernel teams effort to change the user space behaviour (if I understand 
correctly). Only found a single note on how to solve it; add #include 
<linux/compiler.h>. And yes, it compiles nicely. Unfortunatly it doesn't 
link. The i2c_smbus functions are unresolved. So far I found no solution 
for this :'(

So how does the kernel team wants us to access devices? If I understand 
it correctly it is supposed to go through dedicated kernel modules like 
pcf8574 (part of the 2.6 kernel) which are supposed to show up as 
devices in /sys (sysfs). I am using the Gentoo 2.6.10-r6 kernel and a

  modprobe pcf8574

results in a /sys/bus/i2c/devices/0-0020 device. This contains (among 
some other files) a read and write file. Apperently writing to the write 
file should write data to the connected pcf8574. (I haven't tested it yet)

So my question is. Would going for the /sys device be the right solution 
for lcd4linux?

Paul


Michael Reinelt wrote:

> Hi there,
>
>>> I am willing to give it a shot, if you are prepared to provide me 
>>> with some assistance on where to start and how to start. It would be 
>>> my first effort on writing code on linux.
>>
>>
>>
>> No problem, I'm not really a C expert but at least I can help you
>> to follow the 'good line'. :)
>
>
> Hey, would be great if someone would work on this part! I can't be of 
> any help, because I don't have neither an I2C port on my notebook, nor 
> an I2c Interface. But I like the code from Luis, and I think we've got 
> a good framework for using HD44780 over two different busses.
>
> The main reason for the i2c code not working is that most of the code 
> is #ifdef'ed out because I can't get it to compile. maybe some header 
> or something is missing.... I don't know.
>
> Paul, the first thing you'll have to do is getting anonymous CVS 
> access, so you can work on the latest version of the source. If you 
> need assistance with CVS or anything other, please let me know.
>
>
> bye, Michael
>