Question

Inside my kernel-mode driver is the following code:

PHYSICAL_ADDRESS    physAddr;
PVOID               pvk;
unsigned int        reg_addr; // physical address to write to
unsigned int*       reg_val;  // pointer to value to be written

// assume reg_addr and reg_val are initialized to some values

physAddr.QuadPart = (ULONGLONG)reg_addr;
pvk = MmMapIoSpace(physAddr,sizeof(reg_addr),MmNonCached);
WRITE_REGISTER_ULONG((ULONG*)pvk,(ULONG)&reg_val);

The address is not being written to, and I’m not sure why. Is this the correct procedure or am I missing a step? Also, could my pointer arithmetic be wrong? I’ve tried all permutations, and none have resulted in the correct result. I want the physical memory specified by reg_addr to be written with what is specified by the value pointed to by reg_val.

Answer 1

There are a few things that look odd/wrong with your code:-

First, PHYSICAL_ADDRESS.QuadPart is a 64-bit value, but you’re assigning a 32-bit int to it. Are you sure that’s what you want to do?

Second, I assume you want to map a 32-bit ‘ULONG’ register:

pvk = MmMapIoSpace(physAddr,sizeof(reg_addr),MmNonCached); 

That will probably work, but what I think you mean is this

pvk = MmMapIoSpace(physAddr, sizeof(ULONG), MmNonCached); 

Finally, you’re writing the address of the pointer variable reg_val to your register. Your comment implies you want to write the value pointed to by reg_val? If so, use this instead.

WRITE_REGISTER_ULONG((ULONG*)pvk, *reg_val);