I think you can interface to the LCD by using a non-os approach - but you won't have a wealth of information to draw on. The standard Renesas Demo's are all built around the FreeRTOS code. I had never worked with an OS before digging into the Direct Drive GAPI demo to polish up some existing labs. Turns out the OS really doesn't get in the way and was largely invisible to me (I basically just wrote embedded C as normal). I just had to pay attention to setting up my functions intitially. There is a 1668 demo board that you might want to see if you can get your hands on (contact your local Renesas FAE). If you can get a board - and look at the existing Demo - chances are you will have a much better time getting your board doing what you want.
As it was explained to me - as long as you have your pixel clock running - and have the Vsync / Hsync doing the correct thing - and have your enable line going the right direction - you will get pixels out on the screen... maybe in the wrong spots and not stable - but yoiu will get something. That is IF you are shifting out data on your I/O.
So look at your rough timing on the dot clock and vsync/hsync & make sure your enable is going the correct direction. Make sure your backlight is working. The most painful part is getting a stable hello world on screen. After that it gets fun. Make sure and check for opens or bridges in your connector as well. If you can get hold of the 1668 demo board - you can sit with a scope and check all timings of the Demo - then double check them on your board.
Note that if you "go it alone" and bypass the GAPI / RTOS that you will be faced with re-writing 6-12 months worth of code. That is some nasty stuff to tackle if you don't have too.
I would start by going to the www.america.renesas.com/h8lcd page then click on the 2378 kit owner button on the upper right corner - and looking at what is up there for the 2378. (the 1668 version is a work in progress). Note that the demo code can be customized to run on the 1668 pretty easily... I have been playing with the 1668 for several months. The Demo code that comes with the 1668 demo board can be easily set up to run from the SDRAM (I think it is actually configured this way).
The 1668 demo board from Renesas is configured to boot up - then copy contents of the Serial Flash that is on the board to SDRAM (this contains all the Graphics images).
Note you might want to look below the obolete 2378 annotated schematics at the link thta says Annotated Schematics for the H8SX/1668... they might point you in the right direction. Be sure and read over all the notes on the .pdf. You might find a smoking gun in hardware. I have tried to attach the annotated schematic to this post.
