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Author Topic: Does anyone experience or know why Dell PC's have problems with IO Reads?  (Read 7996 times)

Posts: 5

« on: August 24, 2009, 10:23:41 PM »

I have a simple PCI card that utilizes IO addresses.  I send IO Writes and IO Read commands.  Card works great in many PC's... all except some Dell machines.

It seems that when you do a IO read using a tool like TVicPort and read a 16bit or 32bit data, depending on what you read back, the Dell PC will give you bad data.

For example, I create a simple program to write sequential data and read data back after each write.

So example:

1      -   Call Outpw(&H2F8, &H1)
2      -   Call Outpw(&H2F8, &H2)
3      -   Call Outpw(&H2F8, &H3)
4      -   Call Outpw(&H2F8, &H4)
5      -   Call Outpw(&H2F8, &H5)
6      -   Call Outpw(&H2F8, &H6)

Between each writes, I do a IO Read.  I find that the read back occurs liek this:


So you see, why is that some reads, come back 'FFFF' or erronous?  IT just so happens that it is not Random!!  It actually is reproducible, for example.  If I write a hex 4 to that port, then I immediately do a IO read command to the PCI bus, I get back 'FFFF'.  Completely reproducible. 

This problem is reproducible and depending on what the data is, the Dell PC seems to "correct" my read data.  I have made sure that no other devices is sharing the same IO address.

So could anyone telll me why Dell PC's do this?

« Last Edit: August 24, 2009, 10:28:02 PM by nukezero » Logged

Posts: 5

« Reply #1 on: August 24, 2009, 10:25:24 PM »

oh and i need to add, I have tried tons and tonts of port opening programs like UserPort, Direct I/O, Port IO, and TvicPort, all of which is designed to open up the IO ports in Windows XP.

Same problem!  All are reproducible on a late model Dell Optiplex PC.  I am using Visual Basic and have tried many, many different DLL's to do IO writes and IO reads and same problem.


Posts: 5

« Reply #2 on: August 25, 2009, 11:50:43 PM »

After two and a half weeks of troubleshooting, I figured out that some motherboards require Parity generation.

My problem was my card does not generate parity (output) back to the bus.  The bus will give goofy values if the AD lines aren't even parity.

Food for thought.

Posts: 2

« Reply #3 on: November 21, 2009, 07:57:38 AM »

No, not all software runs on Windows 7 just like vista.
But it does have a compatability mode that uses a virtual machine and runs XP.
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