pc386 BSP on board with UMA

[Chris Johns]

Joel Sherrill wrote:
> 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
> 
> =================================================================
> 

Interesting manual. Seems to assume you know what TSEG, SMM etc is.

> The memory sizing algorithm finds 1007MB on this board.

What memory sizing code is this ?

> 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?
> 

I have not followed in detail the size you need to leave, but I would 
have thought the BIOS would have taken this into account for you.

Chris

> Help... :)