Verdin AM62 dual RTC management

Technical Support
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Hi all,

I’m working on a Verdin AM62 board (I’m pretty new to this environment) and I see that 2 RTC devices are available.

One seems a “core” RTC linked to rtc0, that seems to be the main rtc device and is preserved by the VBATT correctly.

There is also another RTC device over i2c bus and used by the wifi module as 32.768Khz clock source. I see this RTC is not preserved by VBATT by default, but it can be enabled by device-tree customization through the attribute .

Which are the foreseen use cases to have 2 RTCs on board? Is the Espon device more precise and shall be used as backup and alignment device for rtc0? Is rtc0 sensible to jitter over time?

Are there some known issues or best practices to best manage RTC usage in this device?

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RTC Configuration on Verdin AM62

Based on the Verdin AM62 documentation, I can clarify the RTC setup and provide guidance on their usage.

RTC Components Overview

The Verdin AM62 features two RTC components with distinct purposes:

  1. Primary RTC (rtc0): This is the SoC’s built-in RTC that serves as the main system clock
  2. External RTC (Epson RX8130CE): A low-power external RTC that provides additional functionality (1)

External RTC Specifications

The Verdin AM62 features a low-power Epson RX8130CE real-time clock (1). This external RTC serves multiple purposes:

  • Clock Source for Wi-Fi Module: The sleep clock input (SLP_CLK_IN) is provided by the RTC (32.768kHz) to the Wi-Fi module (2)
  • Backup Power Support: The external RTC can be powered by VCC_BACKUP supply with a voltage range of 1.1V to 5.5V (typical 3.0V) (3)

Power Supply Configuration

The recommended operation conditions show that the RTC backup power supply (VCC_BACKUP) operates within the following range (3):

  • Minimum: 1.1V
  • Typical: 3.0V
  • Maximum: 5.5V

Use Cases for Dual RTC Setup

The dual RTC configuration serves several purposes:

  1. System Reliability: Having a backup RTC ensures time keeping even if the primary system RTC fails
  2. Power Efficiency: The external RTC can maintain time during deep sleep states when the main SoC is powered down
  3. Wi-Fi Module Support: The external RTC provides the necessary 32.768kHz clock source for the Wi-Fi module’s sleep functionality (2)
  4. Battery Backup: The external RTC can be configured with battery backup to maintain time during complete power loss

Configuration Considerations

Regarding the device tree customization you mentioned, the community has discussed EDLC charging configuration for the RX8130CE (4). The charging functionality can potentially be managed through I2C commands, though specific implementation details may require consulting the RX8130CE datasheet.

Best Practices

For optimal RTC management on the Verdin AM62:

  1. Use rtc0 as Primary: Keep the SoC’s built-in RTC as your primary system clock
  2. Configure Backup Power: Ensure proper VCC_BACKUP supply configuration for the external RTC
  3. Synchronization: Consider implementing synchronization between the two RTCs if high precision is required
  4. Power Management: Leverage the external RTC for maintaining time during low-power states

The external RTC provides enhanced reliability and power management capabilities, making it particularly valuable for applications requiring precise timekeeping during various power states.

Best regards, Toradex AI Assistant.

1 Like
3

could you please compile a device overlay example that enables the backup power of rtc1 to take it as reference for people who will need it for their device?