Re: Driver for Sharp LH155BA

-----Original Message-----
From: Antonino A. Daplas [mailto:adaplas@gmail.com] 
Sent: Tuesday, 1 August 2006 10:36 AM
To: linux-fbdev-devel@lists.sourceforge.net
Cc: rwolf@cardaccess.com.au
Subject: Re: [Linux-fbdev-devel] Driver for Sharp LH155BA

Richard Wolf wrote:

quoted

Hi,

I'm writing a driver for the Sharp LH155BA LCD driver.  This is a 
driver designed for controlling small/medium lcd panels (up 

to 128 x 64 pixels).

quoted

I'm trying to decide whether it is sensible to write a frame buffer 
driver for a device of this nature.  Does the frame buffer 

abstraction 

quoted

make sense for a display this small?

The dimensions of the display does not matter.

quoted

On our target hardware it is not possible to access the 

display memory 

quoted

directly.  Rather, all accesses to display memory and other control 
registers are through a small number of io ports.  

Therefore it is not 

quoted

possible to map display memory.  Is this relevant?

Yes, if the display memory is not mappable, then it won't be 
usable as a driver for X, for example.

You can however allocate a shadow buffer in system RAM which 
can be mmapp'ed.
Then on intervals, perhaps by interrupt or timer, update the 
physical screen.
Unfortunately, this is inefficient, as you may be updating 
the screen even if the shadow buffer haven't changed.  But 
that is the best you can do without hacking the kernel.

Another option is to just forget about mmap, and create your 
own fb_read and fb_write hooks.  This is more efficient, but 
not all apps use this method to update the framebuffer. The 
driver will be usable as a console though.

Tony

Thanks Tony

Presumably if I take the shadow buffer route then I could maintain _two_
shadow buffers.  This would allow me to detect whether the user accessible
buffer had been changed and update the display only when necessary.  

Regards,

Richard


-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys -- and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV

Richard Wolf wrote:

Presumably if I take the shadow buffer route then I could maintain _two_
shadow buffers.  This would allow me to detect whether the user accessible
buffer had been changed and update the display only when necessary.  

Yes, that will work too.

Tony

-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys -- and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV

Antonino A. Daplas wrote:

Richard Wolf wrote:

quoted

Presumably if I take the shadow buffer route then I could maintain _two_
shadow buffers.  This would allow me to detect whether the user accessible
buffer had been changed and update the display only when necessary.  

Yes, that will work too.

check for the epson SED15xx (not sure) driver. sounds like similar 
hardware, same approach.

markus
-- 
_______________________________________________________________________
plain GmbH        | daiserstrasse 15      | 81371 münchen
fon 089.540.149.0 | fax 089.540.149.44    | http://www.plain.de

-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys -- and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV