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8.0

DOS protected mode - PCI memory access error

Asked by Alfredo_Quintero in MS DOS, Network Cards & Adapters, Microsoft Hardware

Tags: dos, pci, memory, access, mode

I am trying to access the dual-port RAM of a PCI device using a DOS extender which allows DOS protected mode operation. I used PCI Sniffer to detect the BIOS assigned resources for this PCI device. It is assigned 8 bytes of I/O port and 256 Kbytes starting from 0x0xDE00_0000. Using MSVS I created a console application which can be executed in DOS thanks to the DOS extender. The application can access the 8 bytes in the I/O area, and I am sure of this since the expected values at startup can be read with the fucntion _inp() and it is possible to write data onto the I/O area with the _outp( , ) function and the LEDs in the front panel bracket change as expected, as per the specification of this specific device. Using the fucntion _outp( , ), the RunCPU bit and MemEna bit of this card are set and the LED turns to the expected behaviour. Setting the MemEna bit of this device should make it possible to access the memory assigned to it by the BIOS, but when issuing the command:

volatile unsigned short * pw;
printf("Offset %8X= %2X",f_wSegment, *pw);

The program crashes with the message:
dkrnl32: exception C0000005, flags=0 occured at BF:430156
ax=225D24 bx=42BBB3 cx=E664A4F dx=493040
si=225D24 di=225EB0 bp=225EB0 sp=225D24
exception caused by access to memory address DE004000
ip = Module 'dn3pcins.exe' + 30156
dkrnl32:fatal exit!

If the protected mode is enabled, why do I get this error?

Thanks.

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[+][-]07/21/07 11:47 AM, ID: 19540221Accepted Solution

Your question has an Asker Certified™ answer! Alfredo_Quintero verified that this solution worked for them--which means it will likely work for you, too. Click to view the solution free for 30-days now.

About this solution

Zones: MS DOS, Network Cards & Adapters, Microsoft Hardware

Tags: dos, pci, memory, access, mode

Solution Provided By: For-Soft

Participating Experts: 2

Solution Grade: A