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EMM28_F.ASM
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Assembly Source File
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1989-11-29
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5KB
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97 lines
;-----------------------------------------------------------------------------;
; MODULE NAME: EMM28_F.ASM ;
; ;
; OS FUNCTION NAME: alloc_DMA_reg_set ;
; ;
; DESCRIPTION: This function gets the number of a DMA register set ;
; for an OS/E, if a DMA register set is currently ;
; available for use. ;
; ;
; In a multitasking operating system, when one task is ;
; waiting for DMA to complete, it is useful to be able to ;
; switch to another task. However, if the DMA is being ;
; mapped through the current register set, the switching ;
; cannot occur. That is, all DMA action must be complete ;
; before any remapping of pages can be done. ;
; ;
; The operating system would initiate a DMA operation on ;
; a specific DMA channel using a specific alternate map ;
; register set. This alternate map register set would ;
; not be used again, by the operating system or an ;
; application, until after the DMA operation is complete. ;
; The operating system guarantees this by not changing ;
; the contents of the alternate map register set, or ;
; allowing an application to change the contents of the ;
; alternate map register set, for the duration of the DMA ;
; operation. ;
; ;
; PASSED: &DMA_reg_set: ;
; is a far pointer to the DMA register set parameter. ;
; ;
; 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. ;
; ;
; DMA_reg_set: ;
; is the DMA register set number. If there are no DMA ;
; register sets supported by the hardware, a zero will ;
; be returned. ;
; ;
; C USE CONVENTION: unsigned int status; ;
; unsigned int DMA_reg_set; ;
; ;
; status = alloc_DMA_reg_set (&DMA_reg_set); ;
;-----------------------------------------------------------------------------;
.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
alloc_DMA_reg_set PROC \
ptr_DMA_reg_set:FAR PTR WORD
;---------------------------------------------------------------------;
; do; ;
; . allocate a DMA register set for use by the OS; ;
;---------------------------------------------------------------------;
MOVE AX, allocate_dma_reg_set_fcn
INT EMM_int
;---------------------------------------------------------------------;
; . pass the DMA register set back to the OS; ;
;---------------------------------------------------------------------;
MOVE DH:DL, 0:BL
MOVE ES:BX, ptr_DMA_reg_set
MOVE ES:[BX], DX
;---------------------------------------------------------------------;
; . return (EMM status); ;
; end; ;
;---------------------------------------------------------------------;
RET_EMM_STAT AH
alloc_DMA_reg_set ENDP
END