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| problems with address 0x00100000 https://forum.osdev.org/viewtopic.php?f=1&t=11240 |
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| Author: | DIGIT4L_PUNK [ Sat Jan 07, 2006 4:47 pm ] |
| Post subject: | problems with address 0x00100000 |
hi I'm working on kernel image loader for DOS. I use flat-real mode to copy the image to the destination memory address (pointed by ES:EDI) when EDI = 0x00100000 (beginnig of the 1st megabyte) after the mem-copy is done, system hangs. and e.g. if EDI = 0x00200000 everithing works fine. so, what's the problem? ??? keep in mind, I have Compaq DeskPro |
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| Author: | kataklinger [ Sat Jan 07, 2006 5:03 pm ] |
| Post subject: | Re:problems with address 0x00100000 |
Flat real mode? Memory area from 0x100000 to 0x10FFEF is known as HMA maybe DOS puts some drivers or TSRs there. |
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| Author: | GLneo [ Sat Jan 07, 2006 5:06 pm ] |
| Post subject: | Re:problems with address 0x00100000 |
try the deleting the command in config.sys:DEVICE=C:\WINDOWS\HIMEM.SYS that should stop dos from puting things in hma, mabey? |
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| Author: | Candy [ Sat Jan 07, 2006 5:09 pm ] |
| Post subject: | Re:problems with address 0x00100000 |
DIGIT4L_PUNK wrote: hi I'm working on kernel image loader for DOS. I use flat-real mode to copy the image to the destination memory address (pointed by ES:EDI) when EDI = 0x00100000 (beginnig of the 1st megabyte) after the mem-copy is done, system hangs. and e.g. if EDI = 0x00200000 everithing works fine. so, what's the problem? ??? keep in mind, I have Compaq DeskPro If your A20 doesn't enable properly, you're memcpy'ing to the IVT and further on. The very next interrupt (random-ish) will crash your system then. If your DOS uses a HMA driver, that crashes your system if the A20 does work. If neither of these, it should work. Note, 0x200000 doesn't use A20 but A21 (and A[19..0]) so it does work if the A20 enable failed. |
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| Author: | DIGIT4L_PUNK [ Sat Jan 07, 2006 5:38 pm ] |
| Post subject: | Re:problems with address 0x00100000 |
I made a test of A20. here it is: Code: mov word [ES:DWORD 0x001b8000],'! ' It shoud print '!' on the screen if the memmory-wrapping was active. ... and I've got a question: when enabling A20 GATE, only 20th bit is enabled?  I knew that entire >=20 bits were enabled when toggling A20 GATE. Am i wrong ???
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| Author: | Candy [ Sun Jan 08, 2006 3:17 am ] |
| Post subject: | Re:problems with address 0x00100000 |
DIGIT4L_PUNK wrote: ... and I've got a question: when enabling A20 GATE, only 20th bit is enabled? I knew that entire >=20 bits were enabled when toggling A20 GATE. Am i wrong ???AFAIK, the A20 gate ONLY controls the A20 line. That means, the A21..A31 line are always on, but that doesn't matter since you can't access them from real-mode anyway. So, if you can't get the A20 enabled, you'll have half your memory in 1M chunks with gaps. |
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