getting data from i/o port

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cylo

Joined: 06 Nov 2004
Posts: 20

cylo 10 Nov 2004, 08:11

hello!

i am realy new in assembler and need to get an memory mapped register adress through a i/o port.

i program on a amd geode gx1 cpu.
http://tech.parvus.com/documents/GeodeGX1.pdf

i need to get the gx_base adress which is saved in the gc register index B8h (p.98 ). to do that i have to use the memory i/o port 22h/23h (p.53). i have to set the index in 22h with a OUT(?) instructuion to get data through the 23h port.

but i dont realy know how the syntax could be look like...

need help! Embarassed

[Matrix_Spell_Checking=adjust,reason="there are memory mapped i/o ports and they are mapped by device ex.: $a000 so use with mov, xor ... so topic name should be without memory"]Matrix[/Matrix_Spell_Checking]

10 Nov 2004, 08:11

Matrix

Joined: 04 Sep 2004
Posts: 1166
Location: Overflow

Matrix 10 Nov 2004, 12:16

howdy,
i recomend you Ralph Brown's Port List,

however in / outis a simple thing

Code:


in al,$60 ; read immediate port till $ff
in ax,$60 ; note: you can't do this with a byte port, unless you wanna read 2 byte ports
in eax,$60 ; note: you can't do this with a byte port, unless you wanna read 4 byte ports

out $60,al ; write immediate port till $ff
out $60,ax ; note: you can't do this with a byte port, unless you wanna write 2 byte ports
out $60,eax ; note: you can't do this with a byte port, unless you wanna write 4 byte ports

mov dx,$378
in al,dx ; read from port dx

in ax,dx ; note: you can't do this with a byte port, unless you wanna read 2 byte ports
in eax,dx ; note: you can't do this with a byte port, unless you wanna read 4 byte ports


mov dx,$378
out dx,al ; read from port dx

out dx,ax ; note: you can't do this with a byte port, unless you wanna write 2 byte ports
out dx,eax ; note: you can't do this with a byte port, unless you wanna write 4 byte ports

10 Nov 2004, 12:16

cylo

Joined: 06 Nov 2004
Posts: 20

cylo 10 Nov 2004, 16:39

Code:

mov dx,$22
mov al,$B8
out dx,al
mov dx,$23
in al,dx
mov al,myvar

i didnt get it... right? Smile

10 Nov 2004, 16:39

bubach

Joined: 17 Sep 2004
Posts: 341
Location: Trollhättan, Sweden

bubach 10 Nov 2004, 17:19

right, except:

Code:

mov [myvar], al

10 Nov 2004, 17:19

Matrix

Joined: 04 Sep 2004
Posts: 1166
Location: Overflow

Matrix 10 Nov 2004, 18:19

yeah, you're right, you can also do this cause posrt number is below 255

Code:

mov al,$B8 
out $22,al 
in al,$23 
mov [myvar],al

myvar rb 1 ; reserve 1 bytes for myvar

however using dx can give the ability for a relocateable port addressing

example:

Code:


mov [baseaddress],$378 ; reset initial value ( printer port 1 )

call readprinterstatus
call readdata

int 20h

readprinterstatus:
mov dx,baseaddress
add dx,1 ; this will read status register
in al,dx
ret

readprinterdata:
mov dx,baseaddress ; this will data port
in al,dx
ret

baseaddress dw $278 ; initial value ( printer port 2 )

10 Nov 2004, 18:19

cylo

Joined: 06 Nov 2004
Posts: 20

cylo 10 Nov 2004, 19:17

okay. this code works better... :p

mov al,$B8
out $22,al
in al,$23
mov [myvar],al

but in the sheet is written that only bit 1:0 of the 8bit gc register has the gx_base adress i need. how can i filter this two bits?

10 Nov 2004, 19:17

ASHLEY4

Joined: 28 Apr 2004
Posts: 376
Location: UK

ASHLEY4 10 Nov 2004, 19:59

The best thing you can do is get this code, it works in the same way as the code you want, but its for sound, you can see from the code how it is done,(not the wav bit, but the AC97 bit).
http://www.programmersheaven.com/zone10/cat592/23237.htm

\\\\||////
(@@)
ASHLEY4.

Batteries not included, Some assembly required.

10 Nov 2004, 19:59

Matrix

Joined: 04 Sep 2004
Posts: 1166
Location: Overflow

Matrix 10 Nov 2004, 19:59

you know basic instructions no?

Code:


;get bit 2 from al
test al,100b ; binary
; now bit is in carry

;get bit 2 from al same with complex 386 microcode
bt ax,2 ; put bit 2 in carry
; now bit is in carry

;or if you don't care al is destroyed do:
and al,100b ; binary
setnz al ; this puts not zero flag in al

;or if you don't care al is destroyed do:
shr al,2 ; shift arithmetical right 2 bits
and al,1 ; mask out bit 0
; now al has the bit 2

;or if you don't care al is destroyed do:
shr al,3 ; shift arithmetical right 2 bits
; now carry has bit 2

;u can use carry like:
jc label1
; not carry
label1:
carry:

10 Nov 2004, 19:59

cylo

Joined: 06 Nov 2004
Posts: 20

cylo 10 Nov 2004, 20:47

okay now i got it...

Code:

and al,3

that gives me the result i am looking for. sorry i am a asm noob Wink

10 Nov 2004, 20:47

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