RTC internal peripheral
目录
Article purpose
The purpose of this article is to
- briefly introduce the RTC peripheral and its main features
- indicate the level of security supported by this hardware block
- explain how it can be allocated to the three runtime contexts and linked to the corresponding software components
- explain, when needed, how to configure the RTC peripheral.
Peripheral overview
The RTC peripheral is used to provide the date and clock to the application. It supports programmable alarms and wake up capabilities.
Features
Refer to 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 RTC peripheral is a secure peripheral.
Peripheral usage and associated software
Boot time
By default after a backup domain power-on reset (performed at boot time), all RTC registers can be read or written in both secure and non-secure modes.
In OpenSTLinux distribution, the first stage bootloader (FSBL, running in secure mode) keeps this default configuration, leaving full control to Linux® at runtime.
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The RTC peripheral is able to generate two interrupts:
- A secure interrupt, connected to the Arm® Cortex®-A7 GIC, not used in OpenSTLinux distribution.
- A non-secure interrupt, connected both to Arm® Cortex®-A7 GIC and Cortex-M4 NVIC: this interrupt is used on Linux® and by default in OpenSTLinux distribution.
The RTC peripheral is part of the backup domain which reset and clock are controlled via the RCC by the first stage bootloader (FSBL, running in secure mode) at boot time.
The RTC reset occurs when the backup domain is reset. To avoid clearing the TAMP register contents, this is only done on cold boot, not on wake up.
Runtime
Overview
The RTC peripheral can be allocated to the Arm® Cortex®-A7 non-secure core to be used under Linux® with RTC framework.
Software frameworks
| Domain | Peripheral | Software frameworks | Comment | ||
|---|---|---|---|---|---|
|
Cortex-A7 secure (OP-TEE) |
Cortex-A7 non-secure (Linux) |
Cortex-M4 (STM32Cube) |
|||
| Core | RTC | Linux RTC framework | |||
Peripheral configuration
The configuration is applied by the firmware running in the context to which the peripheral is assigned. The configuration can be done alone via STM32CubeMX tool for all internal peripherals, and then manually completed (especially for external peripherals) according to the information given in the corresponding software framework article.
For Linux kernel configuration, please refer to RTC device tree configuration.
Peripheral assignment
Internal peripherals assignment table template
| rowspan="1" | Core | rowspan="1" | RTC | RTC | ✓ | ✓ | | RTC is mandatory to resynchronize STGEN after exiting low-power modes. |-
|}
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