Visit the LQ Articles and Editorials section
Go Back > Forums > Linux Forums > Linux - Hardware
User Name
Linux - Hardware This forum is for Hardware issues.
Having trouble installing a piece of hardware? Want to know if that peripheral is compatible with Linux?


  Search this Thread
Old 11-22-2005, 11:29 AM   #1
LQ Newbie
Registered: Nov 2005
Posts: 1

Rep: Reputation: 0
Newbie question about usage of mmap

Hi there,

I have a PCI device and I tried to write a short code to access it in user space with mmap.

first I "cat /proc/bus/pci/devices" and get the device's address: 0x00001800.

then I write the following code:

#include <sys/mman.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

int main(void)
void *map;
int fd;
int src = 0;
ulong base;
ulong length;

base = 0x00001800;
length = 0xFF;

fd = open("/dev/mem", O_RDWR);
map = mmap(NULL, (size_t)length, (PROT_READ | PROT_WRITE), MAP_SHARED, fd,(off_t)base);
if (map == MAP_FAILED)
printf("map failed: %s\n",strerror(errno));

memcpy(map+0x85,&src, 1);

return 0;

I run the code and got the error says that "Invalid Argument", I guess that is because of some misuse of mmap, but where is the error?


Old 11-22-2005, 02:10 PM   #2
Registered: Sep 2005
Location: Old Blighty
Distribution: Slackware, NetBSD
Posts: 536

Rep: Reputation: 30
The offset (the last arg to mmap) must be multiple of the page size (4K on x86, 8K on 64-bit archs). Try just using an offset of zero and taking the 0x1800 into account when accessing the memory.


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
RAM usage question. 99%? TheVrolok Linux - Newbie 2 11-28-2005 09:49 PM
Question about memory usage stefaandk Linux - Newbie 3 08-03-2005 03:22 AM
how to determine cpu usage, memory usage, I/O usage by a particular user logged on li rags2k Programming 4 08-21-2004 05:45 AM
memory usage question bmicielli Linux - Hardware 3 12-27-2003 08:15 PM
CPU usage question infamous41md Linux - Newbie 2 04-01-2003 06:40 PM

All times are GMT -5. The time now is 12:21 AM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration