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This commit is contained in:
Jeff Parsons 2015-04-18 11:05:12 -07:00 • committed by jeffpar
commit ef63a126f5
2 changed files with 92 additions and 34 deletions
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40
devices/pc/bios/compaq/deskpro386/1988-01-28.nasm
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@ -9,29 +9,34 @@
;
; Overview
; --------
; This 32Kb ROM image is ORG'ed at 0x8000, because it needs to run at real-mode
; addresses F000:8000 through F000:FFFF, as well as protected-mode physical addresses
; %FFFF8000 through %FFFFFFFF. Additionally, DeskPro 386 systems mirror this 32Kb ROM
; at real-mode addresses F000:0000 through F000:7FFF, as well as protected-mode physical
; addresses %FFFF0000 through %FFFF7FFF.
; This 32Kb ROM image is ORG'ed at 0x8000, because most of its code is designed to run
; at real-mode addresses F000:8000 through F000:FFFF.
;
; In other words, both 32Kb halves of the top 64Kb of both the first megabyte and the
; 16th megabyte are physically mapped to this ROM image.
; And even though the 80386 resets with CS:IP set to F000:FFF0, the physical base address
; of CS is set to %FFFF0000, which means the ROM must also be mapped at physical addresses
; %FFFF8000 through %FFFFFFFF.
;
; Additionally, DeskPro 386 systems mirror this 32Kb ROM at real-mode address F000:0000
; through F000:7FFF. And that region is similarly mirrored at physical addresses %FFFF0000
; through %FFFF7FFFF.
;
; In other words, both 32Kb halves of the last 64Kb of both the first and last megabyte
; of the 80386's 32Gb address space are physically mapped to this ROM image.
;
; Finally, the DeskPro 386 has a "RAM Relocation" feature that allows 128Kb of RAM at
; %FE0000 through %FFFFFF to be mapped to %0E0000 through %0FFFFF, effectively replacing
; the ROM in the first megabyte with write-protected RAM; the top 64Kb of that RAM must
; first be initialized with the 64Kb at %0F0000 prior to remapping. It's also possible
; to copy external ROMs from %0C0000 through %0EFFFF into the bottom 64Kb of that RAM,
; but this is only done for ROMs known to contain relocatable code (eg, a Compaq Enhanced
; Video Graphics card).
; %00FE0000 through %00FFFFFF to be mapped to %000E0000 through %000FFFFF, effectively
; replacing the ROM in the first megabyte with write-protected RAM; the top 64Kb of that
; RAM must first be initialized with the 64Kb at %000F0000 prior to remapping. It's also
; possible to copy external ROMs from %000C0000 through %000EFFFF into the bottom 64Kb of
; that RAM, but this is only done for ROMs known to contain relocatable code (eg, a Compaq
; Enhanced Video Graphics card).
;
; Every DeskPro 386 system must have a MINIMUM of 1Mb of RAM, of which either 256Kb,
; 512Kb, or 640Kb can be physically mapped as conventional memory (at the bottom of the
; first megabyte), with the remainder (either 768Kb, 512Kb, or 384Kb) physically mapped
; to the top of the 16th megabyte (ending at address %FFFFFF), the last 128Kb of which
; to the top of the 16th megabyte (ending at address %00FFFFFF), the last 128Kb of which
; is used by the "RAM Relocation" feature. The remaining memory immediately below that
; 128Kb (ie, below %FE0000) can only be accessed by special system software, such as CEMM.
; 128Kb (ie, below %00FE0000) can only be accessed by special system software, such as CEMM.
;
; Compaq refers to that remaining memory as "Compaq Built-in Memory".
;
@ -6626,12 +6631,13 @@ xbc71: call xa3e0 ; 0000BC71 E86CE7 '.l.'
call xd6dd ; 0000BCAC E82E1A '...'
;;
;; Relocate the ROM and initialize conventional RAM
;; Switch to protected-mode, relocate the ROM, switch back to real-mode, disable
;; the A20 line, and then initialize all conventional RAM.
;;
call xc825 ; 0000BCAF E8730B
;;
;; This function loads the GDTR with [00FF0730,0047], but since the previous call
;; The next function loads the GDTR with [00FF0730,0047], but since the previous call
;; disabled the A20 line, the first selector load crashes, because physical address
;; %FF0730 requires A20.
;;