In-Line Assembly for I/O Port to Memory Array

[Alan Wirtz]

I can really use some assistance to help me determine why my
simple assembly language subroutine does not function as I would
like. What I need to do is move a number of 16 bit A to D
converter values located at I/O port &H300 to an array in
memory. The A to D values are in a First in-First out memory
that will automatically address the next sample each time an “IN”
instruction to port &H300 is executed. The transfers need to
be done very quickly so have attempted to do the transfers via
in-line assembly in a sub routine. I have established an
ABSOLUTE array starting at &H30000 in which to put the A to D
data values. The following test program shows what I would like
to accomplish. When the program is run, it shows that memory
locations that should have been replaced by the A to D port
values remain as previously initialized.

' Test Program to put A/D Converter Values into memory array
' starting at addres &H30000

DEFINT I 'All "I" Variables are Intergers (%)

DIM ABSOLUTE AtoD??(1:32760) AT &H30000 'Create Large Array Starting
'at address &H30000.
DIM AtoDAddress AS DWORD PTR 'Address pointer to A to D Data
AtoDAddress = &H30000 'Set the AtoD address pointer to the start of AtoD Data
CLS

PRINT "AtoDAddress Pointer is "HEX$(AtoDAddress)
PRINT "Fill part of the AtoD array with known values"
' Want to fill the AtoD array with a seqence of known values
I = 8
W1?? = 0
DO ' Fill AtoD array with words from 0 to 8
@AtoDAddress = W1?? 'put Word value into AtoD array
AtoDAddress = AtoDAddress + 2 ' Increment to next Word address
W1?? = W1?? + 1 'Increment W1
I = I - 1
LOOP While I > 0

PRINT "AtoDAddress Pointer is " HEX$(AtoDAddress)

I = 0
AtoDAddress = &H30000
PRINT "AtoDAddress Pointer is "HEX$(AtoDAddress)
' Want to display the word values in the AtoD array
DO ' Display AtoD array words from locations 0 through 8
W1?? = @AtoDAddress 'put Array value into W1??
PRINT "A/D Array Address/Values " HEX$(AtoDAddress), HEX$(W1??) ' Display
' address then Hex value
AtoDAddress = AtoDAddress + 2 ' Increment to next Word address
I = I + 2
LOOP While I < 16
PRINT "AtoDAddress Pointer is "HEX$(AtoDAddress)

AtoDAddress = &H30000
AddOffset?? = &H0000 ' Set address offset to 0000h
NofS% = 6
PRINT "Called INSTRING SubRoutine " (NofS%) (AddOffset??)

CALL INSTRING(BYVAL NofS%, BYVAL AddOffset??) ' Call INSTRING

I = 0
PRINT "AtoDAddress Pointer is "HEX$(AtoDAddress)
' Want to display the word values in the AtoD array
DO ' Display AtoD array words from locations 0 through 8
W1?? = @AtoDAddress 'put Array value into W1??
PRINT "A/D Array Address/Values is " HEX$(I), HEX$(W1??) ' Display address
'then Hex value
AtoDAddress = AtoDAddress + 2 ' Increment to next Word address
I = I + 2
LOOP While I < 16
PRINT "AtoDAddress Pointer is "HEX$(AtoDAddress)

END

SUB INSTRING(BYVAL No%, BYVAL AddOff??) 'Move A/D Values to memory

! push DI ; Save DI
! pushf ; Save the flag register

! mov AX, &H3000 ; Move the segment 3000H to Register AX
! mov ES, AX ; Move the segment 3000H in AX to Register ES

! mov AX, AddOff?? ; Move Offset address into AX
! mov DI, AX ; Move the Address Offset in AX to Register DI

! mov CX, No% ; Move Number of A/D samples to CX
! mov DX, &H300 ; Move the A/D port address into DX

! cld ; Clear direction flag (to increment addrss pointer)
TRANSDATA:
! in AX, DX ; Input A/D Word from I/O port &H300 & put into AX
! stosw ; Store A/D Word in [AtoDAddress] (ES I), Incr. DI,
! loop TRANSDATA ; Decrement CX. Jump to TRANSDATA if not zero

! popf ; Restore Flag Register
! pop DI ; Restore DI

END SUB

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[Lance Edmonds]

Oh golly.

Firstly, can you be sure there is nothing important at &H30000? Using an arbitary address like that seems quite unwise. Better you should DIM the array normally, then use VARPTR32() to obtain a pointer to the array. If you do so, you should notice the address provided is MUCH higher in memory.

Next, what OS are you running under?

Finally, when you say "does not function as I would like"... can you be a little more specific? What "fails" precisely?

PS: When posting code, please use the [CODE] tags described at http://www.powerbasic.com/support/forums/ubbcode.html - Thanks!

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Alan Wirtz]

Thanks for your response Lance. You seem to have noticed that
am a beginner at programing (this is my first effort to do any
significant programing in any language). The test program that
I included writes known values to the array then reads the known
values back successfully. Then, the subroutine with the assembly
language is called which is supposed to read from I/O port &H300
and put the port values in the array. When the array values are
printed out again, they have not changed from the original values.
I assumed from this result that the assembly language subroutine
is not functioning as I would like.

I know it would be best to dimension an array normally as you
suggest but I can't figure out how to get the Address for the
array into the ES I registers so that I can put the I/O port
values into the correct memory locations. I also need to be
able to address any arbitrary location within the array - not
just the start of the array.

[Alan Wirtz]

I forgot to mention that the operating system I'm using is IBM
PC DOS 7.

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[Lance Edmonds]

Try this to get you going:

 dim x as integer, w(1:32760) as word
 x = varseg(w(1))
 !push DS
 !push DI
 !pushf
 !mov DX, &H300
 !mov ES, x
 !mov DI, 0
 !mov cx, 32760
 !cld
TransData:
 !mov AX, CX  ; test purposes only, substitute "!in AX, DX"
 !stosw
 !loop TransData
 !popf
 !pop DI
 !pop DS
 print "Done! Test values:", w(1), w(16380), w(32760)

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Alan Wirtz]

Lance; Your suggestion works just fine as best I can tell at
this time. Thanks Very Much! I now understand how to pass an
address to an assembly language routine.

I have placed the assembly code inside a Subroutine and I am
passing BYVAL the number of transfers needed (mov CX, N%),
the address segment (mov DS, S%) and the address offset into the
data array (mov DI, o%). Everything seems to work fine but I
would like to know if there are any restrictions to what I use
for the address offset for the DI register other than to keep it
an even number less than 32768?

[Lance Edmonds]

None that spring to mind over and above those you have mentioned.

Of course, you could do more than 32768 elements in your "sample", but you'd have to add code to work across the segment boundary (that's what I love about Windows programming - flat addressing means no segments, and no segment boundary addressing to deal with! )

Have fun with your project!

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>