查看“VREFBUF internal peripheral”的源代码

==Article purpose==
The purpose of this article is to
* briefly introduce the VREFBUF  peripheral and its main features
* indicate the level of security supported by this hardware block
* explain how each instance can be allocated to the three runtime contexts and linked to the corresponding software components
* explain, when needed, how to configure the VREFBUF peripheral.

==Peripheral overview==
The '''VREFBUF''' peripheral is an internal voltage regulator.

===Features===
The VREFBUF is supplied via the VDDA pin. When enabled, it can provide a reference voltage in the range of: 1,5V, 1,8V, 2,048V or 2,5V.

The VREFBUF can be used to provide an analog voltage reference for:
* ADC internal peripheral<ref name="adc_internal">[[ADC internal peripheral]]</ref>
* DAC internal peripheral<ref name="dac_internal">[[DAC internal peripheral]]</ref>
* External components through the dedicated VREF+ pin.

The VREFBUF can be left unused. In this case, an external voltage regulator can provide reference voltage to VREF+ pin.

Refer to the [[STM32MP15 resources#Reference manuals|STM32MP15 reference manuals]] for the complete list of features, and to the software components, introduced below, to know which features are really implemented.

===Security support===
The VREFBUF is a '''non-secure''' peripheral.

==Peripheral usage and associated software==
===Boot time===
The VREFBUF is usually not used at boot time. But it may be needed by the SSBL (see [[Boot chain overview]]), to supply the internal ADC<ref name="adc_internal"/> for example.

===Runtime===
====Overview====
The VREFBUF can be allocated to the Arm<sup>&reg;</sup> Cortex<sup>&reg;</sup>-A7 non-secure to be used under Linux<sup>&reg;</sup> with regulator framework<ref name="regulator">[[Regulator overview]], Linux<sup>&reg;</sup> regulator framework overview</ref>.
{{Info|The VREFBUF is a system resource<ref name="resource manager">[[Resource_manager_for_coprocessing#The_system_resources|Resource manager for coprocessing]], focus on system resources</ref> which needs to be also controlled by the resource manager<ref name="resource manager"/> in case its consumers (e.g. ADC<ref name="adc_internal"/>, DAC<ref name="dac_internal"/> or an external device connected to VREF+ pin) are spread across:
* the Arm<sup>&reg;</sup> Cortex<sup>&reg;</sup>-A7 non-secure context
* the Arm<sup>&reg;</sup> Cortex<sup>&reg;</sup>-M4 context

For this reason, the direct control of VREFBUF from the Arm<sup>&reg;</sup> Cortex<sup>&reg;</sup>-M4 is not recommended in STM32Cube<ref name="STM32Cube">[[STM32CubeMP1 architecture]]</ref> by default.<br/>
It's recommended to implement it in STM32Cube '''only if''' all consumers and the VDDA supply pin are controlled in the Arm<sup>&reg;</sup> Cortex<sup>&reg;</sup>-M4 context.
}}

The [[#Peripheral assignment|Peripheral assignment]] chapter describes which peripheral instance can be assigned to which context.

====Software frameworks====
{{:Internal_peripherals_software_table_template}}
 | Analog
 | [[VREFBUF internal peripheral|VREFBUF]]
 | 
 | Linux [[Regulator overview|regulator]] framework
 |
 |
 |-
 |}

====Peripheral configuration====
The configuration is applied by the firmware running in the context to which the peripheral is assigned. The configuration by itself can be performed via the [[STM32CubeMX]] tool for all internal peripherals. It can then be manually completed (especially for external peripherals) according to the information given in the corresponding software framework article.

* For the Linux kernel configuration, please refer to [[Regulator_overview#Microcontroller_device_internal_regulator|device internal regulator]]. An example can be found also in [[ADC_device_tree_configuration#DT_configuration_example|ADC DT configuration example]]
* In case the control of VREFBUF consumers are spread across the various cores, see also [[Resource manager for coprocessing]]

====Peripheral assignment====
{{:Internal_peripherals_assignment_table_template}}
<onlyinclude>
 | rowspan="1" | Analog
 | rowspan="1" | [[VREFBUF internal peripheral|VREFBUF]]
 | VREFBUF
 | 
 | <span title="assignable peripheral" style="font-size:21px">☐</span>
 |
 | Assignment (single choice)
 |-
</onlyinclude>
 |}

==References==
<references/>