[Gambas-user] Parallel Port - Illegal Seek -

[Doriano Blengino]

mike ha scritto:
> On 04/07/2010 02:47 PM, nando wrote:
>   
>> Seek will not change the address.
>>
>>
>> ---------- Original Message -----------
>> From: Doriano Blengino<doriano.blengino at ...1909...>
>> To: nando_f at ...951..., mailing list for gambas users
>> <gambas-user at lists.sourceforge.net>
>> Sent: Wed, 07 Apr 2010 11:06:42 +0200
>> Subject: Re: [Gambas-user] Parallel Port - Illegal Seek -
>>
>>    
>>     
>>> nando ha scritto:
>>>      
>>>       
>>>> Using SEEK is not correct.
>>>> If you think of the parallel port as a file, you cannot seek.
>>>> It doesn't make sense.
>>>> You can only read and write.
>>>> What are you trying to accomplish ?
>>>> -Fernando
>>>>
>>>>        
>>>>         
>>> He is trying to do low level access to the parallel port, which has 3
>>> hardware addresses.
>>> In that respect, seek() would make sense to select which IO address to
>>> read from/write to.
>>> Whether this works or not, depends on how the kernel driver interprets
>>> the seeks, but the following listing makes it clear that somewhere
>>> (other OSes?) this behavior works.
>>> The error could also arise from other problems: permissions, missing
>>> modules, wrong major/minor numbers and so on...
>>>
>>> Regards,
>>> Doriano
>>>       
How already stated in a previous email, it is possible to access I/O 
ports in different manners.
After a research, I discovered two viable ways - direct access (I don't 
know if gambas has I/O instructions), and /dev/port, which is a device. 
In this last case seek() is used to address a port.

 From http://tldp.org/HOWTO/IO-Port-Programming-2.html :
>
> Another way to access I/O ports is to |open()| |/dev/port| (a 
> character device, major number 1, minor 4) for reading and/or writing 
> (the stdio |f*()| functions have internal buffering, so avoid them). 
> Then |lseek()| to the appropriate byte in the file (file position 0 = 
> port 0x00, file position 1 = port 0x01, and so on), and |read()| or 
> |write()| a byte or word from or to it.
>
> Naturally, for this to work your program needs read/write access to 
> |/dev/port|. This method is probably slower than the normal method 
> above, but does not need compiler optimisation nor |ioperm()|. It 
> doesn't need root access either, if you give a non-root user or group 
> access to |/dev/port| --- but this is a very bad thing... [about 
> security]...
Using /dev/port can be problematic: can gambas do unbuffered I/O?

Other methods would be to use some external program or library (shared 
object). If gambas does not have I/O (peek & poke), then an external 
library is the most performant way, though not the simpler. Gambas can 
interface with external libraries using EXTERNAL declaration.

Googling about this issue, I found some interesting page:
    http://tldp.org/HOWTO/IO-Port-Programming-2.html
    http://www.epanorama.net/circuits/parallel_output.html
    http://www.faqs.org/docs/Linux-mini/IO-Port-Programming.html
    http://cyberelk.net/tim/parport/parport.html
    http://people.redhat.com/twaugh/parport/html/ppdev.html

The best way would be to write a gambas component, having either 
internal I/O instructions (a C component) or relying to an external 
library (a gambas component calling an external library; may be there is 
something already done somewhere).

Hey, gambas gurus out there... someone has the time? I do not.

Regards,
Doriano