Last edited 7 months ago

Clock overview

Applicable for STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

This article gives information about the Linux® Clock framework.
Clocks are generally provided by internal/external oscillators or PLLs.
They can pass through a gate, a muxing, a divider or a multiplier.
All peripheral clocks are organized as a tree.

All these elements are managed by the Common Clock Framework (CCF)

1. Framework purpose[edit source]

The purpose of this article is to introduce the Common Clock Framework. It provides general information and, based on examples, explains how to use it.

Linux Common Clock framework offers a generic API for configuring and controlling the different system clocks.

Drivers can easily enable/disable clocks, change their frequency, change the parent of the clocks associated to peripherals without any knowledge of the clock characteristics.

All clock tree specificities (such as clock source selection, muxing, dividor and gate) are abstracted by the Common Clock framework and the associated system clock driver.

2. System overview[edit source]

RCC
Clock Overview

2.1. Component description[edit source]

  • foo driver: any peripheral driver which needs to control and activate clock(s) associated to a given peripheral.
  • Clock core: the Common Clock framework is the generic Linux kernel interface that controls the clock nodes available in the system.
It features two generic interfaces:
- The upper interface unifies the definition and control of the clocks for all Linux platforms. This agnostic API is used by peripheral drivers for configuring and controlling the clocks associated to a specific peripheral.
- The lower interface allows the registration of platform specific functions in order to manage a platform specific clock tree.
  • clk-stm32mp: STM32 specific clock driver that supports RCC clocks.
  • clk-scmi: SCMI clock driver to manage secured clocks.
  • RCC: reset and clock controler RCC.

2.2. API description[edit source]

Documentation on the Common Clock framework can be found in the kernel documentation:

  • devm_get_clk(): looks up and obtains from the device tree a managed reference to a clock producer, to a root clock or to a clock node.
  • clk_prepare_enable(): selects a parent clock, configures the corresponding multiplexor and dividor, and enables the clock gating.
  • clk_disable_unprepare(): unprepares and gate a clock.
  • clk_get_rate(): obtains the current frequency (in Hz) for a given clock.
  • clk_set_rate(): sets the frequency for a given clock. If a clock has several parents, the clock framework can change the parent in order to obtain a better frequency.
  • clk_get_parent(): gets the parent clock source for a given clock
  • clk_set_parent(): sets the parent clock source for a given clock
  • ...

3. Configuration[edit source]

3.1. Kernel configuration[edit source]

By default the Common Clock framework is activated in the kernel configuration.

3.2. Device tree configuration[edit source]

A detailed device tree configuration is described in Clock device tree configuration.

4. How to use the Common Clock framework[edit source]

This paragraph describes how a standard peripheral driver can retrieve its clock configuration from the device tree and configure it.

The clocks associated to a given peripheral are declared in the device tree as described in https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml.

Specific platform define statements that abstract hardware clock offsets are defined in clock dt-binding header file:

Below an example of clock association(FOO_K) to a foo driver:

	foo: foo@adcdefgh {
               compatible = "foo-driver";
               ...
		clocks = <&rcc FOO_K>;
               ...
	};

Before using the clock specified in the device tree node, the foo driver has to request it at probe execution.

	static int foo_probe(struct platform_device *pdev)
	{
		struct clk *clk;
		...
		clk = devm_clk_get(&pdev->dev, NULL);
		if (IS_ERR(clk)) {
			ret = PTR_ERR(clk);
			dev_err(&pdev->dev, "clk get failed: %d\n", ret);
			goto err_master_put;
		}
		...
	}

The clock can then be configured and enabled using the Common Clock framework API.

If the peripheral needs several clocks, a name must be associated to each clock handle in the device tree node. The specified names must be used by the driver to retrieve the corresponding pointer for each clock.

Below an example of foo driver managing 2 clocks (FOO1_K and FOO2_K):

	foo: foo@abcdefgh {
		compatible = "foo-driver";

		clocks = <&rcc FOO1_K>, <&rcc FOO2_K>;
		clock-names = "foo1", "foo2";
	};
	static int foo_probe(struct platform_device *pdev)
	{
		priv->foo1clk = devm_clk_get(&pdev->dev, "foo1");
		if (IS_ERR(priv->foo1clk)) {
			ret = PTR_ERR(priv->foo1clk);
			if (ret != -ENOENT) {
				dev_err(&pdev->dev, "Can't get 'foo1' clock\n");
				return ret;
			}
		}
  		priv->foo2clk = devm_clk_get(&pdev->dev, "foo2")';
		if (IS_ERR(priv->foo2clk)) {
			ret = PTR_ERR(priv->foo2clk);
			if (ret != -ENOENT) {
				dev_err(&pdev->dev, "Can't get 'foo2' clock\n");
				return ret;
			}
		}
 	 }
	ret = clk_prepare_enable(priv->foo1clk);
	if (ret < 0) {
		dev_err(dev, "foo1 clk enable failed\n");
		goto err_bclk_disable;
	}

5. How to trace and debug the framework[edit source]

5.1. Tracing using dynamic debug[edit source]

By default, no kernel log showing the clock activity. However the user can enable the dynamic debug for the clock framework driver:

dmesg -n8
echo "file drivers/clk/* +p" > /sys/kernel/debug/dynamic_debug/control

Refer to dynamic debug for more details.

5.1.1. How to monitor with debugfs of clock framework[edit source]

Information on clocks are available in Debugfs interface located in the '/sys/kernel/debug/clk' directory.

It helps viewing all the clocks registered in tree format.

Show clock tree:

cat /sys/kernel/debug/clk/clk_summary
 
 clock                          count    count    count        rate   accuracy phase  cycle    enable
-------------------------------------------------------------------------------------------------------
ck_usbo_48m                          1        1        0    48000000          0     0  50000         Y
   usbo_k                            0        0        0    48000000          0     0  50000         N
usart1_k                             0        0        0    64000000          0     0  50000         Y
spi6_k                               0        0        0    64000000          0     0  50000         Y
rtcapb                               1        1        0    66625000          0     0  50000         Y
ck_rtc                               2        2        0       32768          0     0  50000         Y
   rtc_lsco                          1        1        0       32768          0     0  50000         Y
i2c6_k                               0        0        0    64000000          0     0  50000         Y
i2c4_k                               0        0        0    64000000          0     0  50000         Y
hash1                                0        0        0   266500000          0     0  50000         Y
gpioz                                1        1        0   266500000          0     0  50000         Y
cryp1                                0        0        0   266500000          0     0  50000         Y
bsec                                 0        0        0    66625000          0     0  50000         Y
ck_axi                               3        3        0   266500000          0     0  50000         Y
   ck_trace                          0        0        0   133250000          0     0  50000         N
   ck_sys_dbg                        0        0        0   266500000          0     0  50000         Y
   qspi_k                            0        0        0   266500000          0     0  50000         N
   fmc_k                             0        0        0   266500000          0     0  50000         N
   ethstp                            0        0        0   266500000          0     0  50000         N
   usbh                              1        1        0   266500000          0     0  50000         Y
   crc1                              0        0        0   266500000          0     0  50000         N
   ethmac                            1        1        0   266500000          0     0  50000         Y
   ethtx                             1        1        0   266500000          0     0  50000         Y
   gpu                               0        0        0   266500000          0     0  50000         N
   mdma                              0        0        0   266500000          0     0  50000         N
   pclk5                             0        0        0    66625000          0     0  50000         Y
   pclk4                             0        0        0   133250000          0     0  50000         Y
      ddrperfm                       0        0        0   133250000          0     0  50000         N
      stgenro                        0        0        0   133250000          0     0  50000         N
      usbphy                         0        0        0   133250000          0     0  50000         Y
      iwdg2                          0        0        0   133250000          0     0  50000         N
      dsi                            0        0        0   133250000          0     0  50000         N
      ltdc                           0        0        0   133250000          0     0  50000         N
ck_mpu                               0        0        0   650000000          0     0  50000         Y
   ck_mco2                           0        0        0   650000000          0     0  50000         N
pll2_r                               0        0        0   533000000          0     0  50000         Y
pll2_q                               0        0        0   533000000          0     0  50000         Y
   gpu_k                             0        0        0   533000000          0     0  50000         N
ck_lsi                               0        0        0       32000          0     0  50000         Y
   dac12_k                           0        0        0       32000          0     0  50000         N
   rng2_k                            0        0        0       32000          0     0  50000         N
ck_lse                               0        0        0       32768          0     0  50000         Y
   lptim5_k                          0        0        0       32768          0     0  50000         N
   lptim4_k                          0        0        0       32768          0     0  50000         N
   cec_k                             0        0        0       32768          0     0  50000         N
ck_csi                               0        0        0     4000000          0     0  50000         Y
   ck_per                            0        0        0     4000000          0     0  50000         Y
ck_hsi                               1        1        0    64000000          0     0  50000         Y
   ck_mco1                           0        0        0    64000000          0     0  50000         N
   uart8_k                           0        0        0    64000000          0     0  50000         N
   uart7_k                           0        0        0    64000000          0     0  50000         N
   uart6_k                           0        0        0    64000000          0     0  50000         N
   uart5_k                           0        0        0    64000000          0     0  50000         N
   uart4_k                           1        1        0    64000000          0     0  50000         Y
   usart3_k                          0        0        0    64000000          0     0  50000         N
   usart2_k                          0        0        0    64000000          0     0  50000         N
   i2c5_k                            0        0        0    64000000          0     0  50000         N
   i2c3_k                            0        0        0    64000000          0     0  50000         N
   i2c2_k                            0        0        0    64000000          0     0  50000         N
   i2c1_k                            0        0        0    64000000          0     0  50000         N
   spi5_k                            0        0        0    64000000          0     0  50000         N
   spi4_k                            0        0        0    64000000          0     0  50000         N
ck_hse                               4        5        0    24000000          0     0  50000         Y
   usbphy_k                          1        1        0    24000000          0     0  50000         Y
   pll4                              1        1        0   594000000          0     0  50000         Y
      pll4_r                         0        0        0    74250000          0     0  50000         Y
         fdcan_k                     0        0        0    74250000          0     0  50000         N
      pll4_q                         0        0        0    29700000          0     0  50000         N
         ltdc_px                     0        0        0    29700000          0     0  50000         N
         dsi_px                      0        0        0    29700000          0     0  50000         N
      pll4_p                         1        1        0    99000000          0     0  50000         Y
         ck_ker_eth                  2        2        0    99000000          0     0  50000         Y
            ethptp_k                 1        1        0    99000000          0     0  50000         Y
            ethck_k                  1        1        0    99000000          0     0  50000         Y
               ethrx                 1        1        0    99000000          0     0  50000         Y
         spdif_k                     0        0        0    99000000          0     0  50000         N
         sdmmc3_k                    0        0        0    99000000          0     0  50000         N
         sdmmc2_k                    0        0        0    99000000          0     0  50000         N
         sdmmc1_k                    0        0        0    99000000          0     0  50000         N
   pll3                              1        1        0   417755859          0     0  50000         Y
      pll3_r                         0        0        0    11290699          0     0  50000         Y
      pll3_q                         0        0        0    24573875          0     0  47058         Y
         adfsdm_k                    0        0        0    24573875          0     0  50000         N
         adc12_k                     0        0        0    24573875          0     0  50000         Y
         sai4_k                      0        0        0    24573875          0     0  50000         N
         sai3_k                      0        0        0    24573875          0     0  50000         N
         sai2_k                      0        0        0    24573875          0     0  50000         N
         sai1_k                      0        0        0    24573875          0     0  50000         N
         spi3_k                      0        0        0    24573875          0     0  50000         N
         spi2_k                      0        0        0    24573875          0     0  50000         N
         spi1_k                      0        0        0    24573875          0     0  50000         N
      pll3_p                         1        1        0   208877930          0     0  50000         Y
         ck_mcu                     15       15        0   208877930          0     0  50000         Y
            dfsdm_k                  0        0        0   208877930          0     0  50000         N
            gpiok                    0        0        0   208877930          0     0  50000         N
            gpioj                    0        0        0   208877930          0     0  50000         N
            gpioi                    1        1        0   208877930          0     0  50000         Y
            gpioh                    1        1        0   208877930          0     0  50000         Y
            gpiog                    1        1        0   208877930          0     0  50000         Y
            gpiof                    1        1        0   208877930          0     0  50000         Y
            gpioe                    1        1        0   208877930          0     0  50000         Y
            gpiod                    1        1        0   208877930          0     0  50000         Y
            gpioc                    1        1        0   208877930          0     0  50000         Y
            gpiob                    1        1        0   208877930          0     0  50000         Y
            gpioa                    1        1        0   208877930          0     0  50000         Y
            ipcc                     4        4        0   208877930          0     0  50000         Y
            hsem                     1        1        0   208877930          0     0  50000         Y
            crc2                     0        0        0   208877930          0     0  50000         N
            rng2                     0        0        0   208877930          0     0  50000         N
            hash2                    0        0        0   208877930          0     0  50000         N
            cryp2                    0        0        0   208877930          0     0  50000         N
            dcmi                     0        0        0   208877930          0     0  50000         N
            sdmmc3                   0        0        0   208877930          0     0  50000         N
            usbo                     0        0        0   208877930          0     0  50000         N
            adc12                    0        0        0   208877930          0     0  50000         Y
            dmamux                   1        1        0   208877930          0     0  50000         Y
            dma2                     0        0        0   208877930          0     0  50000         N
            dma1                     1        1        0   208877930          0     0  50000         Y
            pclk3                    1        2        0   104438965          0     0  50000         Y
               lptim3_k              0        0        0   104438965          0     0  50000         N
               lptim2_k              0        0        0   104438965          0     0  50000         N
               hdp                   0        0        0   104438965          0     0  50000         N
               pmbctrl               0        0        0   104438965          0     0  50000         N
               tmpsens               1        1        0   104438965          0     0  50000         Y
               vref                  0        0        0   104438965          0     0  50000         Y
               syscfg                0        1        0   104438965          0     0  50000         N
               sai4                  0        0        0   104438965          0     0  50000         N
               lptim5                0        0        0   104438965          0     0  50000         N
               lptim4                0        0        0   104438965          0     0  50000         N
               lptim3                0        0        0   104438965          0     0  50000         N
               lptim2                0        0        0   104438965          0     0  50000         N
            pclk2                    0        0        0   104438965          0     0  50000         Y
               fdcan                 0        0        0   104438965          0     0  50000         N
               dfsdm                 0        0        0   104438965          0     0  50000         N
               sai3                  0        0        0   104438965          0     0  50000         N
               sai2                  0        0        0   104438965          0     0  50000         N
               sai1                  0        0        0   104438965          0     0  50000         N
               usart6                0        0        0   104438965          0     0  50000         N
               spi5                  0        0        0   104438965          0     0  50000         N
               spi4                  0        0        0   104438965          0     0  50000         N
               spi1                  0        0        0   104438965          0     0  50000         N
               tim17                 0        0        0   104438965          0     0  50000         N
               tim16                 0        0        0   104438965          0     0  50000         N
               tim15                 0        0        0   104438965          0     0  50000         N
               tim8                  0        0        0   104438965          0     0  50000         N
               tim1                  0        0        0   104438965          0     0  50000         N
               ck2_tim               0        0        0   208877930          0     0  50000         Y
                  tim17_k            0        0        0   208877930          0     0  50000         N
                  tim16_k            0        0        0   208877930          0     0  50000         N
                  tim15_k            0        0        0   208877930          0     0  50000         N
                  tim8_k             0        0        0   208877930          0     0  50000         N
                  tim1_k             0        0        0   208877930          0     0  50000         N
            pclk1                    0        0        0   104438965          0     0  50000         Y
               lptim1_k              0        0        0   104438965          0     0  50000         N
               mdio                  0        0        0   104438965          0     0  50000         N
               dac12                 0        0        0   104438965          0     0  50000         N
               cec                   0        0        0   104438965          0     0  50000         N
               spdif                 0        0        0   104438965          0     0  50000         N
               i2c5                  0        0        0   104438965          0     0  50000         N
               i2c3                  0        0        0   104438965          0     0  50000         N
               i2c2                  0        0        0   104438965          0     0  50000         N
               i2c1                  0        0        0   104438965          0     0  50000         N
               uart8                 0        0        0   104438965          0     0  50000         N
               uart7                 0        0        0   104438965          0     0  50000         N
               uart5                 0        0        0   104438965          0     0  50000         N
               uart4                 0        0        0   104438965          0     0  50000         Y
               usart3                0        0        0   104438965          0     0  50000         N
               usart2                0        0        0   104438965          0     0  50000         N
               spi3                  0        0        0   104438965          0     0  50000         N
               spi2                  0        0        0   104438965          0     0  50000         N
               lptim1                0        0        0   104438965          0     0  50000         N
               tim14                 0        0        0   104438965          0     0  50000         N
               tim13                 0        0        0   104438965          0     0  50000         N
               tim12                 0        0        0   104438965          0     0  50000         N
               tim7                  0        0        0   104438965          0     0  50000         N
               tim6                  0        0        0   104438965          0     0  50000         N
               tim5                  0        0        0   104438965          0     0  50000         N
               tim4                  0        0        0   104438965          0     0  50000         N
               tim3                  0        0        0   104438965          0     0  50000         N
               tim2                  0        0        0   104438965          0     0  50000         N
               ck1_tim               0        0        0   208877930          0     0  50000         Y
                  tim14_k            0        0        0   208877930          0     0  50000         N
                  tim13_k            0        0        0   208877930          0     0  50000         N
                  tim12_k            0        0        0   208877930          0     0  50000         N
                  tim7_k             0        0        0   208877930          0     0  50000         N
                  tim6_k             0        0        0   208877930          0     0  50000         N
                  tim5_k             0        0        0   208877930          0     0  50000         N
                  tim4_k             0        0        0   208877930          0     0  50000         N
                  tim3_k             0        0        0   208877930          0     0  50000         N
                  tim2_k             0        0        0   208877930          0     0  50000         N
   clk-hse-div2                      0        0        0    12000000          0     0  50000         Y
dsi_k                                0        0        0           0          0     0  50000         N

  • Note: Some clocks are managed by SCMI and necessarily roots (they have no parents from the kernel's point of view).

In addition, each clock has a dedicated directory in which you can find the information such as prepare count, enable count, rate and accuracy:

/sys/kernel/debug/clk# cd usart2_k
/sys/kernel/debug/clk/usart2_k# ls
clk_accuracy      clk_flags           clk_phase             clk_prepare_count
clk_enable_count  clk_notifier_count  clk_possible_parents  clk_rate

Additional information, such as flags, notifier count and possible parents (for clocks with multiple parents) are also available. Just execute a 'cat' command to display them.

/sys/kernel/debug/clk/usart2_k# cat clk_possible_parents 
pclk1 pll4_q ck_hsi ck_csi ck_hse

5.1.2. How to monitor with debugfs of RCC driver[edit source]

Some clocks are managed by the secured world (throught SCMI) and could be not visible from Kernel. Then to have a complete clock summary use a cat command on stm32_clk_summary file.

Show complete clock tree:

cat /sys/kernel/debug/clk/stm32_clk_summary

                                            hardware
   clock                               rate     enable
------------------------------------------------------
ck_hsi                            64000000          Y
   spi4_k                         64000000          N
   spi5_k                         64000000          N
   spi6_k                         64000000          N
   i2c1_k                         64000000          N
   i2c2_k                         64000000          N
   i2c3_k                         64000000          N
   i2c5_k                         64000000          N
   i2c4_k                         64000000          N
   i2c6_k                         64000000          N
   usart1_k                       64000000          N
   usart2_k                       64000000          N
   usart3_k                       64000000          N
   uart4_k                        64000000          Y
   uart5_k                        64000000          N
   uart6_k                        64000000          N
   uart7_k                        64000000          N
   uart8_k                        64000000          N
   ck_mco1                        64000000          N
ck_csi                             4000000          Y
   ck_per                          4000000          ?
ck_lsi                               32000          Y
   rng1_k                            32000          N
   rng2_k                            32000          N
   dac12_k                           32000          N
ck_hse                            24000000          Y
   clk-hse-div2                   12000000          ?
   pll1                          650000000          Y
      pll1_p                     650000000          Y
         pll1_p_div              325000000          ?
         ck_mpu                  650000000          ?
            ck_mco2              650000000          N
   pll2                          533000000          Y
      pll2_p                     266500000          Y
         ck_axi                  266500000          ?
            pclk4                133250000          ?
               ltdc              133250000          N
               dsi               133250000          N
               iwdg2             133250000          N
               usbphy            133250000          Y
               stgenro           133250000          N
               ddrperfm          133250000          N
            pclk5                 66625000          ?
               spi6               66625000          N
               i2c4               66625000          N
               i2c6               66625000          N
               usart1             66625000          N
               rtcapb             66625000          Y
               tzpc               66625000          Y
               iwdg1              66625000          N
               bsec               66625000          Y
               stgen              66625000          Y
            tzc1                 266500000          Y
            tzc2                 266500000          Y
            gpioz                266500000          Y
            cryp1                266500000          N
            hash1                266500000          N
            rng1                 266500000          N
            bkpsram              266500000          N
            mdma                 266500000          N
            gpu                  266500000          N
            ethtx                266500000          Y
            ethrx                266500000          Y
            ethmac               266500000          Y
            crc1                 266500000          N
            usbh                 266500000          Y
            ethstp               266500000          N
            sdmmc1_k             266500000          N
            sdmmc2_k             266500000          N
            fmc_k                266500000          N
            qspi_k               266500000          N
            ck_sys_dbg           266500000          Y
            ck_trace             133250000          N
      pll2_q                     533000000          Y
         gpu_k                   533000000          N
      pll2_r                     533000000          Y
   pll3                          417755859          Y
      pll3_p                     208877930          Y
         ck_mcu                  208877930          ?
            pclk1                104438965          ?
               ck1_tim           208877930          ?
                  tim2_k         208877930          N
                  tim3_k         208877930          N
                  tim4_k         208877930          N
                  tim5_k         208877930          N
                  tim6_k         208877930          N
                  tim7_k         208877930          N
                  tim12_k        208877930          N
                  tim13_k        208877930          N
                  tim14_k        208877930          N
               tim2              104438965          N
               tim3              104438965          N
               tim4              104438965          N
               tim5              104438965          N
               tim6              104438965          N
               tim7              104438965          N
               tim12             104438965          N
               tim13             104438965          N
               tim14             104438965          N
               lptim1            104438965          N
               spi2              104438965          N
               spi3              104438965          N
               usart2            104438965          N
               usart3            104438965          N
               uart4             104438965          Y
               uart5             104438965          N
               uart7             104438965          N
               uart8             104438965          N
               i2c1              104438965          N
               i2c2              104438965          N
               i2c3              104438965          N
               i2c5              104438965          N
               spdif             104438965          N
               cec               104438965          N
               dac12             104438965          N
               mdio              104438965          N
               lptim1_k          104438965          N
            pclk2                104438965          ?
               ck2_tim           208877930          ?
                  tim1_k         208877930          N
                  tim8_k         208877930          N
                  tim15_k        208877930          N
                  tim16_k        208877930          N
                  tim17_k        208877930          N
               tim1              104438965          N
               tim8              104438965          N
               tim15             104438965          N
               tim16             104438965          N
               tim17             104438965          N
               spi1              104438965          N
               spi4              104438965          N
               spi5              104438965          N
               usart6            104438965          N
               sai1              104438965          N
               sai2              104438965          N
               sai3              104438965          N
               dfsdm             104438965          N
               fdcan             104438965          N
            pclk3                104438965          ?
               lptim2            104438965          N
               lptim3            104438965          N
               lptim4            104438965          N
               lptim5            104438965          N
               sai4              104438965          N
               syscfg            104438965          N
               vref              104438965          Y
               tmpsens           104438965          Y
               pmbctrl           104438965          N
               hdp               104438965          N
               lptim2_k          104438965          N
               lptim3_k          104438965          N
            dma1                 208877930          Y
            dma2                 208877930          N
            dmamux               208877930          Y
            adc12                208877930          Y
            usbo                 208877930          N
            sdmmc3               208877930          N
            dcmi                 208877930          N
            cryp2                208877930          N
            hash2                208877930          N
            rng2                 208877930          N
            crc2                 208877930          N
            hsem                 208877930          Y
            ipcc                 208877930          Y
            gpioa                208877930          Y
            gpiob                208877930          Y
            gpioc                208877930          Y
            gpiod                208877930          Y
            gpioe                208877930          Y
            gpiof                208877930          Y
            gpiog                208877930          Y
            gpioh                208877930          Y
            gpioi                208877930          Y
            gpioj                208877930          N
            gpiok                208877930          N
            dfsdm_k              208877930          N
      pll3_q                      24573875          Y
         spi1_k                   24573875          N
         spi2_k                   24573875          N
         spi3_k                   24573875          N
         sai1_k                   24573875          N
         sai2_k                   24573875          N
         sai3_k                   24573875          N
         sai4_k                   24573875          N
         adc12_k                  24573875          Y
         adfsdm_k                 24573875          N
      pll3_r                      11290699          Y
   pll4                          594000000          Y
      pll4_p                      99000000          Y
         sdmmc3_k                 99000000          N
         spdif_k                  99000000          N
         ethck_k                  99000000          Y
         ethptp_k                 99000000          ?
      pll4_q                      29700000          N
         dsi_px                   29700000          N
         ltdc_px                  29700000          N
      pll4_r                      74250000          Y
         fdcan_k                  74250000          N
   usbphy_k                       24000000          Y
   stgen_k                        24000000          Y
ck_lse                               32768          Y
   cec_k                             32768          N
   lptim4_k                          32768          N
   lptim5_k                          32768          N
   ck_rtc                            32768          Y
ck_usbo_48m                       48000000          ?
   usbo_k                         48000000          N
i2s_ckin                                 0          ?

6. Source code location[edit source]

The clock framework is composed of:

7. To go further[edit source]

See "how to build a clock tree" in

8. References[edit source]