Experimental Physics and
Industrial Control System

Jukka Pietarinen <[email protected]> · Fri, 05 Oct 2007 20:39:13 +0300

Emmanuel Mayssat wrote:

To find the pci address in linux, use 'lspci' as root
The PCI address is function of the hardware location (pci slot) in the
computer. So if you fiddle with the hardware that address will change.

The kernel driver should take care of handling the PCI addresses and
provide a method to memory map (mmap) the hardware address into user
space. When this is done the hardware I/O or memory space can be
accessed directly from user space.
. insmod xxx.ko should be called once during system boot (this might not
be correct, maybe just only once then don't have to be called
anymore)???

Look at 'modprobe' instead of 'insmod'. Modprobe loads driver
dependencies, while insmod doesn't.
Look at /etc/modprobe.conf or /etc/modules.conf that is where the driver
configuration goes. Use 'modprobe' in /etc/rc.d/rc.local

Many drivers allocate device numbers dynamically and the major number
assigned can be found from /proc/devices. A device node in /dev has to
be created for each major/minor combination the device is using. After
this the application can open the device /dev/xxx and perform file
operations e.g. mmap.
As an example the Linux kernel driver for the MRF cPCI-EVG is loaded
following:
/sbin/modprobe pci_mrfevg || exit 1
majors=$(awk "\$2==\"mrfevg\" {print \$1}" /proc/devices)
echo "Found" $(echo $majors | wc -w) "Event Generators."
echo "Creating device nodes..."
device=1
for major in $majors; do
    dev=$(echo $device | awk '{ printf "%c", 96+ $1}')
    device=$((++device))
    rm -f /dev/eg$dev[0-3]
    echo "Creating nodes /dev/eg"$dev"[0-3] for major" $major
    mknod '/dev/eg'$dev'0' c $major 0
    mknod '/dev/eg'$dev'1' c $major 1
    mknod '/dev/eg'$dev'2' c $major 2
    mknod '/dev/eg'$dev'3' c $major 3
# Allow write access to members of group mrf
    chgrp mrf '/dev/eg'$dev[0-3]
    chmod g+w '/dev/eg'$dev'3'
done
In this driver minor number 3 provides a direct memory map to a PCI
address space of the hardware.
Below is an excerpt from the API sources for the EVG to show how the

user space access to the EVG registers is gained. The function is called
with "/dev/ega3" as the device name and it return a pointer to a user
space address (*pEg) which the kernel directly maps to hardware.
int EvgOpen(struct MrfEgRegs **pEg, char *device_name)
{
  int fd;
 /* Open Event Generator device for read/write */

fd = open(device_name, O_RDWR);

#ifdef DEBUG

DEBUG_PRINTF("EvgOpen: open(\"%s\", O_RDWR) returned %d\n",
device_name, fd);

#endif

if (fd != -1)

{

/* Memory map Event Generator registers */

*pEg = (struct MrfEgRegs *) mmap(0, EVG_MEM_WINDOW, PROT_READ |
PROT_WRITE, MAP_SHARED, fd, 0);

#ifdef DEBUG

DEBUG_PRINTF("EvgOpen: mmap returned %08x, errno %d\n", (int) *pEg,

errno);

#endif

if (*pEg == MAP_FAILED)

{

close(fd);

return -1;

}

}
  return fd;
}
The sources for MRF CompactPCI EVG/EVR drivers are available from me.
Please let me know if you want a copy.
Regards,
Jukka

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System