Non Standard Timings in fb.modes

[lenny001]

Hi,
I am new to the Rpi (and here), but not to Linux. I have some experience (not a guru) with Linux programming and setup, but the Rpi has such great graphics I am starting a new project.

I want to drive video monitors with the Rpi that have non standard geometry and timings and no EDID chip. I have looked into fbset and fb.modes. I have created new entries in the fb.modes file.

One has been modified from the standard 1280x1024-60 mode and works well.

The other was written from scratch and has a resolution of 1280x1280-60. I know all of the timing parameters and created the entry, but When I run the fbset command it returns the error: ioctl FBIOPUT_VSCREENINFO: Invalid argument.

My question is what is the maximum vertical resolution and maximum pixel clock? Can new entries be added to the fb.modes file and what are their limits? Any advice would be welcome!

Problem entry:

mode "1280x1280-60_low"
#D: 122 MHz, H: 79.12 kHx, V: 59.9 Hz
geometry 1280 1280 1280 1280 8
timings 8026 10 220 40 10 10 10
hsync low
vsync low
endmode

Many Thanks,
Lenny

[lenny001]

Hi Everyone,
Many thanks for giving my rambling post a look. It is a funky question and I have found some of the answers.

It is very possible to edit the fb.modes file and add many other types of display timings/resolutions. Here is a great description of all of the parameters.

The current max number of vertical lines is 1200. I tried my display with those timings and it did work, but really didn't solve my problem. I would suppose that is hard coded in the GPU.

I did not try any other pixel clock settings as that can temporarily charge the LCD with unwanted image retention, so I will leave that for another day.

I did find a great spec here for the Broadcom BCM2835 GPU.

Thanks Again,
Lenny

[-rst-]

I vaguely remember some of the 'big guys' mentioned there is a limit of '1200 vertical'...

It definitely is hardcoded in the framebuffer driver. https://github.com/raspberrypi/linux/bl ... m2708_fb.c line 190:

Code: Select all

if (yres > 1200) {
    pr_err("bcm2708_fb_check_var: ERROR: VerticalTotal >= 1200; "
                 "special treatment required! (TODO)\n");
    return -EINVAL;
}

...which most likely explains your error message.