Implementing FB driver for serial attached TFT

[Markus Rudolf <rudolf@mpch-mainz.mpg.de>]

I'm currently using an embedded ARM920 board running kernel 2.6.5.

I designed a custom hardware using my onboard FPGA to attach a serial controlled
small TFT (actually it's a display from a mobile phone which uses some sort of
SPI to communicate) to my CPU.

The display supports 132 pixel horizontal and 176 pixel vertical resolution, and
uses a 16bit 565RGB color encoding per pixel.

I want to code a framebuffer driver for it to keep the application software as
portable as possible (thought about using directFB or something like that
later).

I guess the vfb.c code is a good base to start from.

As the display does not have memory mappable RAM I need to use some kernel
memory as framebuffer and copy this memory via the serial link to the display
(thought about usig a kernel thread and / or interrupt handler, as the transfer
logic in the FPGA has a 512 word FIFO with interrupt signaling if the FIFO runs
empty. Did that to free some CPU time).

What kind of changes do I have to do to the vfb.c regarding the setup of the
capabilities (resolution / color scheme)? I didn't got that stuff with those
different color coding schemes. If someone could point out what mode would be
best for my display I would really appreciate.

If I use the framebuffer console, will the console automatically adjust its size
to the small display or how can I set a correct mode here ?

I also read that it's impossible to mmap() the kernel memory, but that most FB
applications will try to do so. How can I fix this issue ?

Many questions, I know, but I'm really a bit lost.

Thanks for any comments !

Markus



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