[U-Boot-Users] U-Boot Memory Allocation for Framebuffer?

Michael Bendzick michaelb at logicpd.com
Tue Jul 27 20:38:39 CEST 2004

I'm doing some development on a LCD framebuffer for the OMAP 1510 Innovator
board (ARM925T CPU), and am encountering some difficulties with code flying
off to strange places.

I'm theorizing that the code flies off because memory is not properly
allocated for the framebuffer.  I'm basing all of my new U-Boot related code
on cpu/mpc8xx/lcd.c, and adding LCD code from the OMAP kernel to get a final

I make use of this code from lib_arm/board.c:

	 * reserve memory for LCD display (always full pages)
	/* bss_end is defined in the board-specific linker script */
	addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
	size = lcd_setmem (addr);
	gd->fb_base = addr;
#endif /* CONFIG_LCD */

I have a lcd_setmem function that works fine, but I don't think the memory
map gets properly initialized once it knows how much framebuffer memory is

As the board initializes, "U-Boot code: 11080000 -> 1109D7B0  BSS: ->
110A1DA0" is printed, and the call lcd_setmem(0x110a2000) happens.
lcd_setmem wants to reserve the size 0x13000, which causes 'addr' in the
above code block to be 1108f000, and that is the location of the

With the framebuffer occupying 1108f000 to 110A2000, that leaves only
1108000 to 1108f000 for U-Boot.  Taking a look at disassembly of the binary,
there is definitely valid code in the framebuffer range.

I'm wondering how the code block above, which also appears in roughly the
same form in lib_ppc/board.c, is supposed to grab a block of free memory for
the framebuffer.  Do I need to just allocate uchar
framebuffer[col*row*depth+palette] and point the framebuffer address to that
instead?  Something else?


-Michael Bendzick
Systems and Software Engineering
Logic Product Development
michael.b at logicpd.com

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