====== flink Linux Kernel Modules ======

<box blue right 42% | **Downloads**>
  * [[https://github.com/flink-project/flinklinux | flink Linux Kernel Modules on Github]]
</box>

This is the user documentation for the flink kernel modules. They offer drivers capabilities to communicate with various hardware interfaces. For more information about the inner workings see [[https://github.com/flink-project/flinklinux|flink Linux Kernel Modules on Github]]. The driver API can be found under [[http://api.flink-project.ch/doc/flinklinux/html|API]]

===== Overview =====
When flink is used on a Linux based system the flink library in userspace communicates with the hardware by means of several kernel modules. The basic module is ''flink.ko''. Further, every flink device needs one more kernel module for each hardware interface which is used to communicate with an external FPGA. This could be ''flink_pci.ko'', ''flink_spi.ko'', ''flink_lpb'', ''flink_axi'' or ''flink_eim''. They use the appropriate underlying subsystem for the particular bus. 

===== Requirements =====
  * Linux based operating system
  * GCC 4.6 or newer
  * GNU make

===== Building =====
  * Clone git repository: <code>git clone https://github.com/flink-project/flinklinux.git --recursive
cd flinklinux
git submodule init
git submodule update</code>
  * Choose the target plattform and find its appropriate kernel configuration together with the kernel headers. Find more help about this in [[https://www.debian.org/releases/stable/i386/ch08s06.html.en|Compiling a New Kernel]] \\ \\
  * Build for the host plattform with: <code>make</code>
  * Build for a plattform different from the host with: <code>make ARCH=arch CROSS_COMPILE=comp KERNELDIR=path</code> with the following settings
    * ''arch'': target plattform such as ''powerpc'' or ''arm'' 
    * ''comp'': cross compiler such as ''powerpc-linux-gnu-'' or ''arm-linux-gnueabi-''
    * ''path'': path to kernel headers \\ \\
  * The makefile will switch to the kernel directory, read the current configuration and compile all necessary flink kernel modules for the choosen target plattform.
  * Use ''depmod'' to create suitable dependency files for the new modules. This step is not necessary if modules are loaded with ''insmod''.

===== Generating the documentation =====
Create the makefile with cmake (in the root directory): <code>cmake .</code>
After this generate the documentation as given in the ''Doxyfile'' by : <code>make doc</code>
===== Installation =====
  * Move new kernel modules into the default location to ''/lib/modules/version'' of the target plattform.
  * Load each module with ''insmod'', e.g. <code>insmod flink.ko</code>
  * If dependency files were created beforehand its better to use <code>modprobe flink.ko</code>
  * Some kernel module must be loaded with the appropriate arguments according to the target board specifications (see below)

===== Module Parameters =====
Determine the availabe parameters for each kernel module with the command ''modinfo''. The following table shows the currently available modules with their parameters.
^ module ^ parameters ^ description ^ example ^
| flink.ko | | core module | |
| flink_pci.ko | vendor id, product id| for pci interface | flink_pci vid=0x1172 (Altera) pid=4 |
| flink_spi.ko | device memory length (see below) | for spi interface | flink_spi dev_mem_length=0x280 |
| mpc5200/flink_lpb.ko | device memory length (see below) | for local plus bus | mpc5200/flink_lpb dev_mem_length=0x280 |
| imx6/flink_eim.ko | | for EIM bus |  |
| zynq/flink_axi.ko |either hardcoded into module or reading device tree node| for AXI bus |  |

Busses like //PCI// have discoverability built into them. Any device connected to such a bus can tell the system, what kind of device it is and what resources it uses. On the //SPI// this is not possible. Therefore, you must provide the total device memory length when loading the module. This length is determined by the number and types of the subdevices implemented in VHDL, see [[flink_vhdl|flink VHDL]]. \\ If an //info subdevice// is present, it will give the information about the total device size and the parameter can be ommitted, see [[flink_vhdl#info_subdevice|Info Subdevice]]. 

===== Performance =====
When parallel busses such as PCI or LocalPlusBus are used, any flink transfer happens very quickly and basically depends on the speed of the bus and the FPGA. Care has to be taken when using the SPI interface. The standard SPI subsystem in a standard Linux distribution uses an internal queueing mechanism which is rather slow. Subsequent transfers of a message are separated by approximately 70μs. Further, every flink read or write includes a 8 byte transfer (address and data phase). Though SPI allows for full duplex transfers this feature cannot be used here.\\
IMPORTANT When using SPI timing considerations become crucial. As a rule of thumb: Every flink transfer (such as updating a PWM high time or reading a encoder value takes up to 200μs. SPI should be used for low-frequency control application with not too many parallel channels.