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EMM30_A.ASM
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Assembly Source File
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1989-11-29
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8KB
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135 lines
;-----------------------------------------------------------------------------;
; MODULE NAME: EMM30_A.ASM ;
; ;
; OS FUNCTION NAME: enable_OS_fcns ;
; ;
; DESCRIPTION: This function provides an OS/E with the ability to ;
; enable all programs or device drivers to use the OS/E ;
; specific functions. The capability is provided ONLY ;
; for an OS/E which manages regions of mappable ;
; conventional memory and cannot permit programs to use ;
; any of the functions which affect mappable conventional ;
; memory regions, but must be able to use these functions ;
; itself. When an OS/E disables these functions and a ;
; program attempts to use them, the memory manager ;
; returns a status to the program indicating that the ;
; OS/E has denied the program access to the function. In ;
; other words, the functions will not work when disabled. ;
; However, all programs may use them when enabled. ;
; ;
; The OS/E (Operating System/Environment) functions this ;
; function enables are: ;
; get_hw_info enable_DMA_reg_set ;
; get_alt_reg_set disable_DMA_reg_set ;
; set_alt_reg_set dealloc_DMA_reg_set ;
; get_alt_context_size enable_OS_fcns ;
; alloc_alt_reg_set disable_OS_fcns ;
; dealloc_alt_reg_set return_OS_access_key ;
; alloc_DMA_reg_set ;
; ;
; It appears contradictory that the OS/E can re-enable ;
; these functions when the function which re-enables them ;
; is itself disabled. An overview of the process follows.;
; ;
; The memory manager enables all the OS/E specific ;
; functions, including this one, when it is loaded. The ;
; OS/E gets exclusive access to these functions by ;
; invoking either of the Enable/Disable OS/E Function Set ;
; functions before any other software does. ;
; ;
; On the first invocation of either of these functions, ;
; the memory manager returns an access_key which the OS/E ;
; must use in all future invocations of either of these ;
; functions. The memory manager does not require the ;
; access_key on the first invocation of the ;
; Enable/Disable OS/E Function Set functions. ;
; ;
; On all subsequent invocations, the access_key is ;
; required for either the Enable or Disable OS/E Function ;
; Set functions. Since the access_key is returned only ;
; on the first invocation of the Enable/Disable OS/E ;
; Function Set functions, and presumably the OS/E is the ;
; first software to invoke this function, only the OS/E ;
; obtains a copy of this key. The memory manager must ;
; return an access key with a random value, a fixed value ;
; key defeats the purpose of providing this level of ;
; security for an OS/E. ;
; ;
; PASSED: &access_key: ;
; is a far pointer to an access key which EMM will ;
; initialize. The OS/E must use this key whenever it ;
; needs to access the OS/E specific EMM functions. ;
; ;
; RETURNED: status: ;
; is the status EMM returns from the call. All other ;
; returned results are valid only if the status ;
; returned is zero. Otherwise they are undefined. ;
; ;
; access_key: ;
; is an EMM initialized access key which the OS/E must ;
; use whenever it needs to access the OS/E specific ;
; EMM functions. Returned only on the first function ;
; invocation, the memory manager returns a random ;
; valued key which will be required thereafter for the ;
; execution of this function. On all invocations ;
; after the first, the correct key is not returned. ;
; ;
; C USE CONVENTION: unsigned int status; ;
; unsigned long access_key; ;
; ;
; status = enable_OS_fcns (&access_key); ;
;-----------------------------------------------------------------------------;
.XLIST
PAGE 60,132
IFDEF SMALL
.MODEL SMALL, C
ENDIF
IFDEF MEDIUM
.MODEL MEDIUM, C
ENDIF
IFDEF LARGE
.MODEL LARGE, C
ENDIF
IFDEF COMPACT
.MODEL COMPACT, C
ENDIF
IFDEF HUGE
.MODEL HUGE, C
ENDIF
INCLUDE emmlib.equ
INCLUDE emmlib.str
INCLUDE emmlib.mac
.LIST
.CODE
enable_OS_fcns PROC \
USES DI, \
ptr_access_key:FAR PTR DWORD
;---------------------------------------------------------------------;
; do; ;
; . enable the OS related functions & obtain an "access key" ;
; . required for future use of these functions; ;
;---------------------------------------------------------------------;
MOVE AX, enable_os_fcn_set_fcn
MOVE ES:DI, ptr_access_key
MOVE BX:CX, ES:[DI]
INT EMM_int
;---------------------------------------------------------------------;
; . pass the "access key" back to the OS; ;
;---------------------------------------------------------------------;
MOVE ES:[DI], BX:CX
;---------------------------------------------------------------------;
; . return (EMM status); ;
; end; ;
;---------------------------------------------------------------------;
RET_EMM_STAT AH
enable_OS_fcns ENDP
END