Re: Using framebuffer device under Linux

[Lawrence <lawrencio@hotpop.com>]

Hi Karsten,

Thank you very much for your invaluable adivce. Your assumption is 
right. I've set the color bit to 24bit so that the program fail. After 
setting it back to 8 bit, the program works elegantly.

Next I'll examine the code carefully in order to grasp the assets in it.

Thanks again for all your help.

Best Regards,
Lawrence

Karsten Scheibler ??:

>Hello Lawrence,
>
>  
>
>>Thanks for your suggestion. here is what I got from strace:
>>
>>execve("./fb", ["./fb"], [/* 18 vars */]) = 0
>>ioctl(0, 0x4b3b, 0x80492e8)             = 0
>>ioctl(0, 0x4b3a, 0x1)                   = 0
>>open("/dev/fb0", O_RDWR)                = 3
>>ioctl(3, 0x4600, 0x804931c)             = 0
>>ioctl(3, 0x4604, 0x80492ec)             = 0
>>ioctl(3, 0x4601, 0x80493bc)             = -1 EINVAL (Invalid argument)
>>ioctl(3, 0x4601, 0x804931c)             = 0
>>ioctl(3, 0x4605, 0x80492ec)             = 0
>>ioctl(0, 0x4b3a, 0)                     = 0
>>_exit(1)                                = ?
>>
>>
>>The system call in question seems on setting screen parameters.  But I 
>>don't know how to deal with this.  Could you please give me some hints?
>>    
>>
>
>The fb example code tries to change the colordepth to 8bpp. That brings me to
>the assumption that you use vesafb with another colordepth. vesafb is unable
>to change colordepth after boot. All "real" fb drivers allow that, vesafb
>not, due to BIOS calling limitations after boot. You should
>change your vga= line which is passed to the kernel, to a mode with 8bpp.
>
>If 
>
>cat /proc/fb
>
>outputs something like
>
>0 VESA
>
>then my assumption is right. Otherwise i would be interested in additional
>information about your system (kernelversion etc.).
>
>You may try to execute
>
>fbset
>
>to see your current fb parameters
>
>
>
>karsten
>-
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>  
>