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Blog post update

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This commit is contained in:
Jeff Parsons 2016-01-21 22:54:47 -08:00
commit 8eb1e0aa21
2 changed files with 19 additions and 19 deletions
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24
_posts/2015-04-16-compaq-deskpro-386-update.md
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@ -111,18 +111,18 @@ three physical address ranges at any time, regardless whether A20 is disabled or
Which is a good thing, because I came across at least one code sequence in the ROM BIOS that enters
protected-mode with A20 disabled -- an unwise thing to do on most machines:
;;
;; When we arrive here, the A20 line has been disabled; on most systems, that would
;; mean that the ROM's GDT would only be accessible at the "low" ROM address (%0F0730),
;; not the "high" address (%FF0730). But fortunately, A20 management on Compaq
;; DeskPros affects wrap-around only from the 1st to the 2nd megabyte; no other address
;; range is affected.
;;
;; FYI, it seems this code doesn't do anything if bits 6 and 7 of the RAM Settings
;; register are set to anything other than 0x40 (ie, it returns to real-mode almost
;; immediately after entering protected-mode).
;;
lgdt [cs:0x077e] ; 0000F498 load [gdtr_hi] into GDTR
;
; When we arrive here, the A20 line has been disabled; on most systems, that would
; mean that the ROM's GDT would only be accessible at the "low" ROM address (%0F0730),
; not the "high" address (%FF0730). But fortunately, A20 management on Compaq
; DeskPros affects wrap-around only from the 1st to the 2nd megabyte; no other address
; range is affected.
;
; FYI, it seems this code doesn't do anything if bits 6 and 7 of the RAM Settings
; register are set to anything other than 0x40 (ie, it returns to real-mode almost
; immediately after entering protected-mode).
;
lgdt [cs:0x077e] ; 0000F498 2E0F01167E07; load [gdtr_hi] into GDTR
mov eax,cr0 ; 0000F49E 0F2000
or ax,0x1 ; 0000F4A1 0D0100
mov cr0,eax ; 0000F4A4 0F2200

6
docs/README.md
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@ -16,14 +16,14 @@ Help is available for the following JavaScript Machines:
{% if page.developer %}
Assorted documentation is also available for programming the machines:
Instruction documentation is also available:
* [6502 Instructions](/docs/6502/)
* [x86 Instructions](/docs/x86/)
* [6502 Instructions](/docs/6502/)
{% endif %}
Our [Publication Archive](/pubs/) also includes these PC-related resources:
Our [Publication Archive](/pubs/) includes these PC-related resources:
* [Datasheets](/pubs/pc/datasheets/)
* [Magazines](/pubs/pc/magazines/)