10. What are kernel modules and how are they loaded in linuxRT?In the linux world, kernel modules are pieces of code that can be loaded and unloaded into the kernel upon demand.
They extend the functionality of the kernel without the need to reboot the system.
For example, one type of module is the device driver, which allows the kernel to access hardware connected to the system.
Without modules, we would have to build monolithic kernels and add new functionality directly into the kernel image.
Besides having larger kernels, this has the disadvantage of requiring us to rebuild and reboot the kernel every time we want new functionality.
linuxRT too, lets you load and unload kernel modules dynamically.
Now we are ready to load some kernel modules essential to our ioc - like EVR.
In our 'startup.cmd' script, we have the following line which lets us customize and load our kernel modules:
/afs/slac/g/lcls/epics/iocCommon/ioc-b34-bd32/kernel-modules.cmd
The location for kernel modules is specified as an environment variable in linuxRT:
KERNEL_DRIVER_HOME=/afs/slac/g/lcls/package/linuxKernel_Modules
There are several linux and linuxRT drivers in this directory.: Linux Kernel Modules
The PCI EVR230 driver is here. The following driver version has been built for the latest linuxRT 3.14.12-rt9: EVR230_PCI_EVR_DRIVER=$KERNEL_DRIVER_HOME/pci_mrfevr_linuxRT/buildroot-2014.08
The PCI Express EVR300 driver built for linuxRT 3.14.12-rt9, is here:
EVR300_PCI_EVR_DRIVER=$KERNEL_DRIVER_HOME/pci_mrfev300_linuxRT/buildroot-2014.08
The kernel drivers are installed (loaded) dynamically as follows: # Load the MRF EVR230 Kernel Module for timing
insmod $EVR230_PCI_EVR_DRIVER/pci_mrfevr.ko
$EVR230_PCI_EVR_DRIVER/module_load # Load the MRF EVR300 Kernel Module for timing
insmod $EVR300_PCI_EVR_DRIVER/pci_mrfevr300.ko
$EVR300_PCI_EVR_DRIVER/module_load
There are a couple of things to note:
1. Currently the EVR kernel modules SW has the restriction that if there are both a PMC EVR230 and a PCI-e EVR300 in a linux box,
then the PMC EVR230 MUST BE initialized as card 0 and loaded first. EVR300 must be initialized as card 1.
Additionally, due to hard-coded device names in the module, it is essential to setup the following links:
ln -s /dev/er3a0 /dev/erb0
ln -s /dev/er3a1 /dev/erb1
ln -s /dev/er3a2 /dev/erb2
ln -s /dev/er3a3 /dev/erb3 2. If only one EVR (either PMC EVR230 or PCI EVR300) is installed in your system, then the above restriction does not apply and soft links are not needed.
Take a look at the following script:
/afs/slac/g/lcls/package/linuxKernel_Modules/pci_mrfev300_linuxRT/buildroot-2014.08/module_load
Notice how kernel modules are loaded as device drivers under the /dev/ in linuxRT much like linux.
3. The Broadcom Ethernet NIC driver used to be a separate kernel module and its dirver was loaded dynamically via ;modprobe tg3' in this script.
With the latest linuxRT version 3.14.12-rt9, this step has become unnecessary as the driver has become part of this linuxRT boot image.
4. The SIS digitizers for uTCA, loads their device drivers in 'kernel-modules.cmd':
SIS8300_DRIVER=$KERNEL_DRIVER_HOME/sis8300drv/MAIN_TRUNK
modprobe uio
insmod $SIS8300_DRIVER/sis8300drv.ko
Please note that as of date, SIS8300 has NOT been rebuilt for the latest linuxRT 3.14.12-rt9.
It is currently unsupported on COTS Linux servers. For convinience, you can setup a soft link to your ioc's home directory in kernel-modules.cmd as below: ln -s /afs/slac/g/lcls/epics/iocCommon/ioc-b34-bd32 /home/laci/ioc-b34-bd32
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