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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 |
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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 |
#3
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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? |
#4
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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 |
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