pc386 BSP on board with UMA

[Joel Sherrill]

Hi,

I have been debugging a lock up during initialization
on an embedded PC with 1GB RAM but the last part is
reserved for video, etc.. See Section 5.4 in this
manual.

=================================================================
http://www.intel.com/assets/pdf/datasheet/252615.pdf

Voids of physical addresses that are not accessible as general system 
memory and reside within
system memory address range (< TOM) are created for SMM-mode and legacy 
VGA graphics
compatibility. It is the responsibility of BIOS to properly initialize 
these regions. The number
of UMA options has been extended. Allocation is at a fixed address in 
terms of rigid positioning
of UMA system memory 􀃆TOM-TSEG-UMA(size), but it is mapped at any 
available address by
a PCI allocation algorithm. GMADR and MMADR are requested through BARs.
The following table details the location and attributes of the regions.

Table 33. Pre-allocated System Memory
System Memory Segments Attributes Comments
00000000H - 03E7FFFFH R/W Available system memory 62.5 -MB
03E80000H - 03F7FFFFH R/W Pre-allocated Graphics VGA memory
1-MB (or 4/8/16/32- MB) when IGD is
enabled
03F80000H - 03FFFFFFH SMM Mode Only - CPU Reads TSEG Address Range
03F80000H - 03FFFFFFH SMM Mode Only - CPU Reads TSEG Pre-allocated 
system memory

=================================================================

The memory sizing algorithm finds 1007MB on this board. But
if you clear all of that memory, the system locks up. If I
decrease that to 1004MB, things work. My reading of the
above is that we shouldn't touch the last 64MB RAM.

Does that make sense? Is there some way to know this?

Help... :)

-- 
Joel Sherrill, Ph.D.             Director of Research&  Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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