Using DOS debug, how to read bios/chipset registers? \ VOGONS

Using DOS debug, how to read bios/chipset registers?

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First post, by GigAHerZ

Posted on 2020-12-23, 09:43

GigAHerZ Offline

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I think it should be possible, yet, i have absolutely no knowledge in that low level programming. Therefore, maybe one of you can help me out?

I would like to match some jumpers on board with some register values in chipset using datasheet. For that, i need a way to read certain addresses to see, if some bits have flipped, when i have changed the jumper settings. (obviously, jumpered bits are read-only)

Maybe someone can help me out and show, how to use dos debug for example to read some register addresses? Let's say, i want to see all 8 bits on register 60h in chipset. What should i write?

Thank you!

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!

Reply 1 of 8, by Tiido

Posted on 2020-12-23, 12:31

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Start QBASIC instead and use the INP and OUT functions to do things

OUT &H60, 123 'write 123 to $60
PRINT INP(&H60) 'show content of $60 on screen

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Reply 2 of 8, by GigAHerZ

Posted on 2020-12-23, 14:41

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Seems like i've been slightly off track.
I found this thing here in the forum: "As explained in the data sheet, the chipset registers are accessed through port I/O. $22 is the index port and $23 is the data port."

So what would that mean? Always write to 22h and then read back from 23h?

Last edited by GigAHerZ on 2020-12-23, 15:17. Edited 2 times in total.

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!

Reply 3 of 8, by BloodyCactus

Posted on 2020-12-23, 14:43

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well if you wanted to set a value to a port, you wouldnt use debug necessarily unless you wanted to write asm that way.

start debug and type;

a
mov dx,060
mov al,0FF
out dx,al
mov ah,04c
int 021

rip
100
g

the "a" is for assemble, then you have lines of code setting the port and the value in al
the 4c/cd21 is to exit the app

rip sets the instruction pointer to 100
g runs the program

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Reply 4 of 8, by GigAHerZ

Posted on 2020-12-23, 15:17

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GigAHerZ wrote on 2020-12-23, 14:41:

Seems like i've been slightly off track.
I found this thing here in the forum: "As explained in the data sheet, the chipset registers are accessed through port I/O. $22 is the index port and $23 is the data port."

So what would that mean? Always write to 22h and then read back from 23h?

I ask and i answer: Yes, this is how it works. Write register address to 22h and then read 23h for the value. Thanks, @Tiido, as you gave everything i needed, both reading and writing.

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!

Reply 5 of 8, by maxtherabbit

Posted on 2020-12-23, 15:50

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you can do direct port IO in DEBUG, no need for BASIC or any assembly

-i 60

-o 60 FF

Reply 6 of 8, by maxtherabbit

Posted on 2020-12-23, 15:54

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are you familiar with the program CTCHIP34? if your chipset is supported it provides an easy front end to changing chipset register values

Reply 7 of 8, by GigAHerZ

Posted on 2020-12-23, 16:15

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maxtherabbit wrote on 2020-12-23, 15:54:

are you familiar with the program CTCHIP34? if your chipset is supported it provides an easy front end to changing chipset register values

Now i know! Yep, i can see same values there. Thanks!

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!

Reply 8 of 8, by BloodyCactus

Posted on 2020-12-23, 21:29

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maxtherabbit wrote on 2020-12-23, 15:50:

you can do direct port IO in DEBUG, no need for BASIC or any assembly

-i 60

-o 60 FF

heh I never knew that one! I use debugx which is a better debug ... 386 regs, and indeed the I (w|d) port functions.

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