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Question about VRAM setting in dm8168

1330hayacool7102
Guru 10655 points


After looking "TMS320DM81XX Graphics Control Using Frame Buffer Driver.pdf", I have a question about the following description

Given below are the basic steps to open FBDev nodes and draw GUI in display.
1) Boot kernel with at least 16M VRAM size.   ==> why there's a limitation in VRAM about 16M??

Any one know that?

  • 0
    TI__Mastermind 20245 points

    Hi,

    This is because by default when ti81xxfb.ko is inserted it allocates buffer for 1920X1080 resolution and it requires almost 16MB for that buffer. Buffer is allocated using this VRAM memory.

    Regards,

    Hardik Shah

  • 0 in reply to HardikShah
    Guru 10655 points

    Thanks. Hardik.
    1. can you caculate the value of 16M? 1920x1080x2x3(3 graphic layer) ?? how did you get the value?
    2. if the limitation is at lease 16M, why did you set vram=40M in the document? 40M-16M=24M. What's the usage of 24M?

  • 0 in reply to 1330hayacool7102
    TI__Guru 66380 points

    Please see my comments below.

    Regards,

    yihe

    Medwin Tsai said:

    Thanks. Hardik.
    1. can you caculate the value of 16M? 1920x1080x2x3(3 graphic layer) ?? how did you get the value?

    [yihe] 16M = 1920x1080*4(1 ARGB32 1080P buffer) * 2(2 such buffer)
    2. if the limitation is at lease 16M, why did you set vram=40M in the document? 40M-16M=24M. What's the usage of 24M?

    [yihe] there are three fbdev drivers, two HD and one SD, the 24 is for the second HD and SD framebuffer.