Re: I want to know how to write a lcd driver with spi interface

From: peter meng
Date: Mon Dec 01 2008 - 22:40:56 EST


Thank you very mach .
I'm a newbie on video driver .
Could you recommended the lcd driver that already use spi interface on Linux to me ?
I want to emulate it .

Best Regards

--- On Tue, 12/2/08, Iwo Mergler <iwo@xxxxxxxxxxxxxxxxxx> wrote:

> From: Iwo Mergler <iwo@xxxxxxxxxxxxxxxxxx>
> Subject: Re: I want to know how to write a lcd driver with spi interface
> To: mengsanshui@xxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Date: Tuesday, December 2, 2008, 7:09 AM
> peter meng wrote:
> > 1. I want to know how to write a lcd driver with spi
> interface on
> > linux(2.6.24) ? I'm using a
> tft-lcd(FT-G128160UTSW-123W-E vendor --TRULY)
> > with s6d0151(IC) that connected to s3c2412 with spi
> .
> > interface : SDI --> GPG6 WR-->GPG7 CSB
> -->GPG3 RS-->GPB1 RESET -->GPB2 )
> >
> > 2.How the framebuffer related with spi interface ? I
> mean how the
> > framebuffer know it transfer the data with spi
> interfcae not the
> > RGB/80-System interface.
> The main difference is that a framebuffer is memory mapped,
> whereas an SPI
> connected display is more suitable for a function call
> abstraction. The two don't
> relate very well.
> Your SPI display has an internal frame buffer, which you
> can access via SPI,
> but cannot memory map. A function call interface would
> easily map to the
> SPI transfer, but requires applications written for such an
> API.
> If you absolutely have to use a framebuffer abstraction,
> you can create a fake
> framebuffer in RAM. Now, you have to solve the problem of
> keeping the display's
> framebuffer in sync with the RAM one.
> The simplest approach is to have a kernel timer fire a few
> times per second
> and transfer the whole RAM fb via SPI every time. The
> faster you refresh, the
> better the synchronisation, but you'll hit CPU or SPI
> bus limits eventually. It
> also causes image artefacts with fast updating content,
> e.g. video.
> If your CPU+RAM is much faster than SPI, it might be
> beneficial to detect
> which part of the display was changed and only update that
> stripe/rectangle.
> In practice, it is best to use a combination of methods.
> Have a timer based
> update for most GUI-type applications and then modify the
> more demanding
> applications to control the refresh directly, for instance
> through a IOCTL.
> If your applications use a graphics library on top of the
> framebuffer (e.g. QTE),
> you may be able to add synchronisation calls into that
> library, for better
> efficiency.
> One more avenue to look at is to use the MMU for
> synchronisation. That is,
> you map the RAM fb as read only, such that if an
> application writes to it, it triggers
> an exception. In the exception handler you remap the memory
> as read/write,
> execute the write, update the display and remap r/o. This
> would be very inefficient,
> so you may want to leave the memory mapped r/w and start a
> timer to collect a
> number of changes before mapping r/o again.
> The best method very much depends on your use case,
> applications, relative
> speeds of CPU and SPI, size of display, etc.
> >
> > 3. Where i can get the example driver on linux ?
> A well documented framebuffer skeleton:
> drivers/video/skeletonfb.c
> A RAM-based framebuffer: drivers/video/vfb.c
> A simple SPI driver (EEPROM): drivers/spi/at25.c
> Kind regards,
> Iwo

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