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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', ...).
As part of this node configuration, SYSCLK frequency should also be defined, using
"clock-frequency" property.
Last, bus clocks (typically HCLK, PCLK1, PCLK2) should be configured using matching
prescaler properties.
Here is an example of correctly configured rcc node:
&rcc {
         clocks = <&pll>;  /* Set pll as SYSCLK source */
         clock-frequency = <DT_FREQ_M(80)>; /* SYSCLK runs at 80MHz */
         ahb-prescaler = <1>;
         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.

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

ahb-prescaler

int

 
AHB prescaler. Sets a HCLK frequency (feeding Cortex-M Systick)
lower than SYSCLK frequency (actual core frequency).
Zephyr doesn't make a difference today between these two clocks.
Changing this prescaler is not allowed until it is made possible to
use them independently in Zephyr clock subsystem.

Legal values: 1

apb1-prescaler

int

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

apb2-prescaler

int

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

Specifier cell names

  • clock cells: bus, bits