[syslinux] COM32 question

[H. Peter Anvin]

ganapathy murali krishnan wrote:
> I am new to 32-bit programming in DOS. So this might be a stupid question.
> 
> How do I access an absolute memory location in my COM32 code. If I 
> understand it correctly, all the memory addresses use virtual addresses. 
> I need to write code to read an absolute location in memory
> 
> Is it as simple as
> 
> answer = *(unsigned char *)MK_PTR(seg,ofs)
> 
> or does the fact that the COM32 code is runing using virtual addresses 
> complicate matters.
> 

COM32 actually doesn't use virtual addresses at all, it uses 32-bit flat 
addresses.  MK_PTR() and SEG()/OFFS() can be used to convert 32-bit flat 
addresses from/to 16-bit real-mode segment:offset type pointers, as long 
as the address falls in the first megabyte of memory.

The first megabyte restriction is important, that's why you need the low 
memory bounce buffer.

	-hpa