We have been thinking about new Carambola mother board with integrated MCU. But for now it is not clear should it be "arduino" powered atmega or more powerful MCU like Cortex.

I already suggested that a few posts ago and Sprite_tm has even provided me with a link to his website where he did something similar for another embedded system project. My original suggestion was to use the STM32F407 (discovery board is cheaply available), which runs on 168MHz has decently sized memory (1MB flash and 192kB RAM) and it even has an LCD interface. I suppose that this microcontroller is even powerfull enough to make it into a real USB - VGA/TV graphics card (with an R2R DAC or dedicated DAC chip).

But I liked the minimalistic idea of using just those simple USB to parallel chips to control small displays via USB. Those chips are easier to solder than the STM32F407, and you could solder them to SSOP28 adapter boards for fast and easy prototyping.
I guess the advantage would be that you'd only need to develop the driver software on the Carambola to work with the USB to parallel bridge, as opposed to also writing a decent firmware to run on the STM32.

In the end the STM32 solution would clearly be the best and most versatile option. One could even think about redesigning the current Carambola dev board to include the USB graphics card (with on board USB HUB of course) and provide video out to those projects that might need it.[/quote]

Kernel driver and firmware for Cortex isn't problem but IMHO this solution will be very expensive.Better solution would be to use cheap mcu with hardware LCD support like Rockchip (12$) or something like this and to add wifi SIP module (5$) if you need wifi radio.

Gedass: You may want to take a look at the FT245 and the FT2232HS. The first is an 8-bit fifo-style usb1.1 interface which can send the data fairly quickly (iirc at the maximum usb1 allows) with only one or two externel parts; the second one is a kick-arse usb2.0 high speed interfacing IC with quite a lot of options, including emulating a standard uC-style address/databus. It oughtto be a breeze to connect an LCD to that. Writing a driver should be possible too, though it's a bit more work because you'd have to implement talking to the FTxxx-chip in kernelspace. (Current implementations for non-serial use are userspace-based, iirc.)

If you're thinking about including a companion chip in the Carambola-build: may I suggest a small-ish FPGA directly connected to some kind of high-speed bus, preferably with DMA-support? That way, anyone who wants it can whip up a desired peripherial, or even just download it from opencores.org or something. That'd allow almost any peripherial possible, from a 16-port serial driver to a VGA framebuffer.

I've had a look at the datasheet for the FT2232HS. Sounds like it'd be the perfect match to extend the Carambolas peripheral abilities with a USB LCD interface. With 32 high speed I/O lines it could control an LCD and read data from a camera module like the OV7670...

FYI: I've finished my article. It includes all the necessary schematics and patches for the Carambola kernel. Read it here: http://spritesmods.com/?art=spitft