This is the documentation for the latest (main) development branch of Zephyr. If you are looking for the documentation of previous releases, use the drop-down menu on the left and select the desired version.

st,stm32-rcc

Vendor: STMicroelectronics

Description

STM32 Reset and Clock controller node.
This node is in charge of system clock ('SYSCLK') source selection and controlling
clocks for AHB (Advanced High Performance) and APB (Advanced Peripheral) bus domains.

Configuring STM32 Reset and Clock controller node:

System clock source should be selected amongst the clock nodes available in "clocks"
node (typically 'clk_hse, clk_hsi', 'pll', ...).
Core clock frequency should also be defined, using "clock-frequency" property.
Note:
        Core clock frequency  = SYSCLK / AHB prescaler
Last, peripheral bus clocks (typically PCLK1, PCLK2) should be configured using matching
prescaler properties.
Here is an example of correctly configured rcc node:
&rcc {
         clocks = <&pll>;  /* Select 80MHz pll as SYSCLK source */
         ahb-prescaler = <2>;
         clock-frequency = <DT_FREQ_M(40)>; /* = SYSCLK / AHB prescaler */
         apb1-presacler = <1>;
         apb2-presacler = <1>;
}

Specifying a gated clock:

To specify a gated clock, a peripheral should define a "clocks" property encoded
in the following way:
... {
         ...
         clocks = <&rcc STM32_CLOCK_BUS_APB2 0x00000020>;
         ...
}
After the phandle referring to rcc node, the first index specifies the registers of
the bus controlling the peripheral and the second index specifies the bit used to
control the peripheral clock in that bus register.

Specifying an alternate clock source:

Specifying an alternate source clock could be done by adding a clock specifier to the
clock property:
... {
         ...
         clocks = <&rcc STM32_CLOCK_BUS_APB2 0x00000020>,
                      <&rcc STM32_SRC_HSI I2C1_SEL(2)>;
         ...
}
In this example I2C1 device is assigned HSI as clock source.
It is device driver's responsibility to querry and use clock source information in
accordance with clock_control API specifications.

Properties

Properties not inherited from the base binding file.

Name

Type

Details

#clock-cells

int

Number of items to expect in a Clock specifier

This property is required.

Constant value: 2

clock-frequency

int

default frequency in Hz for clock output

This property is required.

ahb-prescaler

int

AHB prescaler. Defines actual core clock frequency (HCLK)
based on system frequency input.
The HCLK clocks CPU, AHB, memories and DMA.

This property is required.

Legal values: 1, 2, 4, 8, 16, 64, 128, 256, 512

apb1-prescaler

int

This property is required.

Legal values: 1, 2, 4, 8, 16

apb2-prescaler

int

This property is required.

Legal values: 1, 2, 4, 8, 16

undershoot-prevention

boolean

On some parts, it could be required to set up highest core frequencies
(>80MHz) in two steps in order to prevent undershoot.
This is done by applying an intermediate AHB prescaler before switching
System Clock source to PLL. Once done, prescaler is set back to expected
value.

Specifier cell names

  • clock cells: bus, bits