accessing memory mapped I/O in REAL MODE of x86 processor Arch..

hi all,

can any one clarify below points,

1. can we access the Peripheral registers which are of size 255 bytes
(memory-mapped) in real mode which consists of 1Mbyte of space only..
?

or we must access them in only protected mode ?

2. Which is going to edit GDT, LDT,IDT in a system, is it OPERATING
SYSTEM or BIOS(boot loader) ?

3. is there any reserved space in REAL MODE 1MB where we should not
map any custom pheripheral(memory map)..

with regards,
bhanu prakash.k

banu wrote:
hi all,

can any one clarify below points,

1. can we access the Peripheral registers which are of size 255 bytes
(memory-mapped) in real mode which consists of 1Mbyte of space only..
?

or we must access them in only protected mode ?

2. Which is going to edit GDT, LDT,IDT in a system, is it OPERATING
SYSTEM or BIOS(boot loader) ?

3. is there any reserved space in REAL MODE 1MB where we should not
map any custom pheripheral(memory map)..

?? Your question makes very little sense, but I'll try to answer it. ??

In real mode, the most reserved part of memory is the region between
0-640MB, where they map the general-purpose RAM. Between 640MB-1024MB region
is the section where you can map registers. However, be aware that there are
some standard periperals that always occupy the same locations in memory
such as the BIOS, the video BIOS, the video graphics buffer, etc.

http://www.osdata.com/system/physical/memmap.htm

Yousuf Khan

Yousuf Khan wrote:

banu wrote:
hi all,

can any one clarify below points,

1. can we access the Peripheral registers which are of size 255 bytes
(memory-mapped) in real mode which consists of 1Mbyte of space only..
?

or we must access them in only protected mode ?

2. Which is going to edit GDT, LDT,IDT in a system, is it OPERATING
SYSTEM or BIOS(boot loader) ?

3. is there any reserved space in REAL MODE 1MB where we should not
map any custom pheripheral(memory map)..

?? Your question makes very little sense, but I'll try to answer it. ??

In real mode, the most reserved part of memory is the region between
0-640MB, where they map the general-purpose RAM. Between 640MB-1024MB
region is the section where you can map registers. However, be aware that
there are some standard periperals that always occupy the same locations
in memory such as the BIOS, the video BIOS, the video graphics buffer,
etc.

http://www.osdata.com/system/physical/memmap.htm

Yousuf Khan

Ehhmm, dont you mean KB and not MB?

Eric wrote:
In real mode, the most reserved part of memory is the region between
0-640MB, where they map the general-purpose RAM. Between 640MB-1024MB
region is the section where you can map registers. However, be aware
that there are some standard periperals that always occupy the same
locations in memory such as the BIOS, the video BIOS, the video
graphics buffer, etc.

http://www.osdata.com/system/physical/memmap.htm

Yousuf Khan

Ehhmm, dont you mean KB and not MB?

Damn, you're right. I'm just in the process of getting used to using GB's
instead of MB's mostly, and now I have to think back to the ancient days
about DOS. :-)

Yousuf Khan