.. _clock_control_litex_sample:
LiteX Clock Control Driver Sample
#################################
Introduction
************
This sample is providing an overview of LiteX clock control driver capabilities.
The driver uses Mixed Mode Clock Manager (MMCM) module to generate up to 7 clocks with defined phase, frequency and duty cycle.
Requirements
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* LiteX-capable FPGA platform with MMCM modules (for example Digilent Arty A7 development board)
* SoC configuration with VexRiscv soft CPU and Xilinx 7-series MMCM interface in LiteX (S7MMCM module)
* Optional: clock output signals redirected to output pins for testing
Configuration
*************
Basic configuration of the driver, including default settings for clock outputs, is held in Device Tree clock control nodes.
.. literalinclude:: ../../../dts/riscv/riscv32-litex-vexriscv.dtsi
:start-at: clk0: clock-controller@0 {
:end-at: };
.. literalinclude:: ../../../dts/riscv/riscv32-litex-vexriscv.dtsi
:start-at: clk1: clock-controller@1 {
:end-at: };
.. literalinclude:: ../../../dts/riscv/riscv32-litex-vexriscv.dtsi
:start-at: clock0: clock@82005000 {
:end-at: };
This configuration defines 2 clock outputs: ``clk0`` and ``clk1`` with default frequency set to 100MHz, 0 degrees phase offset and 50% duty cycle. Special care should be taken when defining values for FPGA-specific configuration (parameters from ``litex,divclk-divide-min`` to ``litex,vco-margin``).
**Important note:** ``reg`` properties in ``clk0`` and ``clk1`` nodes reference the clock output number (``clkout_nr``)
Driver Usage
************
The driver is interfaced with the :ref:`Clock Control API <clock_control_api>` function ``clock_control_on()`` and a LiteX driver specific structure:
.. doxygenstruct:: litex_clk_setup
:project: Zephyr
| To change clock parameter it is needed to cast a pointer to structure ``litex_clk_setup`` onto ``clock_control_subsys_t`` and use it with ``clock_control_on()``.
| This code will try to set on ``clk0`` frequency 50MHz, 90 degrees of phase offset and 75% duty cycle.
.. code-block:: c
struct device *dev;
int ret;
struct litex_clk_setup setup = {
.clkout_nr = 0,
.rate = 50000000,
.duty = 75,
.phase = 90
};
dev = DEVICE_DT_GET(MMCM);
clock_control_subsys_t sub_system = (clock_control_subsys_t*)&setup;
if ((ret = clock_control_on(dev, sub_system)) != 0) {
LOG_ERR("Set CLKOUT%d param error!", setup.clkout_nr);
return ret;
}
Clock output status (frequency, duty and phase offset) can be acquired with function ``clock_control_get_status()`` and clock output frequency only can be queried with ``clock_control_get_rate()``
In both getter functions, basic usage is similar to ``clock_control_on()``. Structure ``litex_clk_setup`` is used to set ``clkout_nr`` of clock output from which data is to be acquired.
Sample usage
************
This example provides a simple way of checking various clock output settings. User can pick one of 4 possible scenarios:
* Frequency range,
* Duty cycle range,
* Phase range,
* Setting frequency, duty and phase at once, then check clock status and rate,
Scenarios are selected by defining ``LITEX_CLK_TEST`` as one of:
* ``LITEX_TEST_FREQUENCY``
* ``LITEX_TEST_DUTY``
* ``LITEX_TEST_PHASE``
* ``LITEX_TEST_SINGLE``
Code is performed on 2 clock outputs with ``clkout_nr`` defined in ``LITEX_CLK_TEST_CLK1`` and ``LITEX_CLK_TEST_CLK2``. Tests are controlled by separate defines for each scenario.
Building
********
.. code-block:: none
west build -b litex_vexriscv zephyr/samples/drivers/clock_control
Drivers prints a lot of useful debugging information to the log. It is highly recommended to enable logging and synchronous processing of log messages and set log level to ``Info``.
Sample output
*************
.. code-block:: none
[00:00:00.200,000] <inf> CLK_CTRL_LITEX: CLKOUT0: set rate: 100000000 HZ
[00:00:00.240,000] <inf> CLK_CTRL_LITEX: CLKOUT1: updated rate: 100000000 to 100000000 HZ
[00:00:00.280,000] <inf> CLK_CTRL_LITEX: CLKOUT0: set duty: 50%
[00:00:00.320,000] <inf> CLK_CTRL_LITEX: CLKOUT0: set phase: 0 deg
[00:00:00.360,000] <inf> CLK_CTRL_LITEX: CLKOUT1: set rate: 100000000 HZ
[00:00:00.400,000] <inf> CLK_CTRL_LITEX: CLKOUT1: set duty: 50%
[00:00:00.440,000] <inf> CLK_CTRL_LITEX: CLKOUT1: set phase: 0 deg
[00:00:00.440,000] <inf> CLK_CTRL_LITEX: LiteX Clock Control driver initialized
*** Booting Zephyr OS build zephyr-v2.2.0-2810-g1ca5dda196c3 ***
Clock Control Example! riscv32
device name: clock0
clock control device is 0x40013460, name is clock0
Clock test
Single test
[00:00:00.510,000] <inf> CLK_CTRL_LITEX: CLKOUT0: set rate: 15000000 HZ
[00:00:00.550,000] <inf> CLK_CTRL_LITEX: CLKOUT0: set phase: 90 deg
[00:00:00.590,000] <inf> CLK_CTRL_LITEX: CLKOUT0: set duty: 25%
[00:00:00.630,000] <inf> CLK_CTRL_LITEX: CLKOUT1: set rate: 15000000 HZ
[00:00:00.670,000] <inf> CLK_CTRL_LITEX: CLKOUT1: set duty: 75%
Getters test
CLKOUT0: get_status: rate:15000000 phase:90 duty:25
CLKOUT0: get_rate:15000000
CLKOUT1: get_status: rate:15000000 phase:0 duty:75
CLKOUT1: get_rate:15000000
Clock test done returning: 0
References
**********
- :ref:`litex-vexriscv`
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