IBM PC CONVERTIBLE Technical Reference page 156

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DMiLSETUP
THIS ROUTINE SETS UP THE DMA FOR READ/WRITE/VERIFY OPERATIONS.
INPUT
(AL) = MODE BYTE FOR THE DMA
(ES) - SEGMENT TO READ/WRITE THE DATA
(BP) - STACK POINTER (TO GET INPUT PARAMETERS)
OUTPUT
(AX,CX) DESTROYED
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02Fl
DMiLSETUP PROC NEAR
02Fl
FA CLI NO MORE INTERRUPTS
02F2 E6 OC OUT DMA+12,AL
SET THE FIRST/LAST F/F
02F4 EB 00 JMP
$+2
DELAY FOR DMA CONTROLLER
02F6
E6 OB OUT DMA+11,AL OUTPUT THE MODE BYTE
02F8 50 PUSH AX SAVE COMMAND
02F9 8C CO MOV
AX, ES GET THE ES VALUE
02FB Bl 04 MOV
CL,4 SHI FT COUNT
02FD 03 CO ROL AX,CL ROTATE LEFT
02FF
8A E8 MOV CH,AL GET HIGHEST NYBLE OF ES TO CH
0301 24 FO AND AL,OFOH ZERO THE LOW NYBBLE FROM SEGMENT
0303 03 46 OC
ADD AX,BXSAVE[BP] ADD ADDRESS OFFSET
0306 73 02
JNC J33 TEST FOR CARRY FROM ADDITION
0308 FE C5 INC CH CARRY MEANS HIGH 4 BITS MUST BE INC
030A J33 :
030A 50 PUSH AX SAVE START ADDRESS
030B
E6 04
OUT DMA+4,AL OUTPUT LOW ADDRESS
0300 8A C4
MOV AL,AH
030F E6 04 OUT DMA+4,AL OUTPUT HIGH ADDRESS
0311 8A C5
MOV AL,CH GET HIGH 4 BITS
0313 24 OF
AND AL ,OFH
0315 E6 81 OUT DMiLPAGE2,AL OUTPUT THE HIGH 4 BITS TO
DETERMINE COUNT
0317 8A 66 OE
MOV AH,ALSAVE[BP] NUMBER OF SECTORS (AL SAVE)
031A 2A CO SUB AL,AL TIMES 256 INTO AX
031C 01 E8
SHR AX,1
SECTORS
*
128 INTO AX
031E 50 PUSH
AX
031F BB 0006 MOV BX,6 GET THE BYTES/SECTOR PARM
0322 E8 0259 R CALL GELPARM
0325 8A CC MOV CL,AH USE AS SHIFT COUNT (0=128, 1=256 ETC)
0327 58 POP
AX
0328 03 EO SHL
AX,CL MUL TIPLY BY CORRECT AMOUNT
032A 48 DEC AX -1 FOR DMA VALUE
032B 50 PUSH AX
SAVE COUNT VALUE
032C E6 05 OUT DMA+5,AL
LOW BYTE OF COUNT
032E 8A C4 MOV AL,AH
0330 E6 05 OUT DMA+5,AL HIGH BYTE OF COUNT
0332 FB STI I NTERRUPTS BACK ON
0333 59 POP
CX RECOVER COUNT VALUE
0334 58 POP
AX RECOVER ADDRESS VALUE
0335 03 Cl ADD AX,CX ADD, TEST FOR 64K OVERFLOW
0337 BO 02 MOV
AL,2 MODE FOR 8237
0339 E6 OA OUT
DMA+lO,AL INITIALIZE THE DISKETTE CHANNEL
033B 58 POP AX RESTORE COMMAND
033C 73 OE JNC DMiLOUT
033E 3C 42 CMP
AL,42H NON-DMA OPERATION?
0340 74 OA
JE
DMiLOUT I F SO THEN NO BOUNDRY ERROR
0342 C6 06 0041 R 09 MOV DISKETTE_STATUS,DMA_BOUNDARY ; SET DMA BOUNDRY ERROR
0347 C6 46 OE 00 MOV BYTE PTR [BP+14] ,0
NO SECTORS TRANSFERRED (AL SAVE)
034B F9
STC SET CARRY TO INDICATE ERROR
034C DMA_OUT:
034C
C3 RET RETURN TO CALLER,
CARRY SET BY ABOV ElF ERROR
0340
DMiLSETUP ENDP
ROM BIOS 2-131