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Automatically Save and Load Snapshot Image Mode

Last modified by Microchip on 2026/08/17 15:51

Overview

In restore mode, at91bootstrap automatically saves the current contents of Double Data Rate (DDR) memory—including the Linux® system state, kernel, and running applications—as a snapshot image to flash memory.

On the next boot, everything is loaded back from the snapshot image into DDR and all running applications are restored immediately, thereby bypassing most of the traditional boot sequence.

fast boot workflow

Applicable Scenarios

This is ideal for scenarios where extremely fast boot times are required, and system state must be preserved seamlessly after a reboot. For example, embedded systems in industrial automation or consumer electronics can utilize this mode to minimize boot times.

Supported Devices and Prerequisites

  • Supported devices
    • SAMA5D2 (including SAMA5D2-SIP)
    • SAMA7G54
    • SAMA7D65
    • Not supported: SAM9X60 and SAM9X7
  • Hardware Requirements
    • Power Management Integrated Circuit (PMIC) is not necessary
  • Software Requirements
    • PM mode support: Restore mode (new)
    • Unlike Mode 1, Backup mode, Mode 2 uses the new Restore mode. All power supplies remain on, and Linux asserts a Central Processing Unit (CPU) reset to let at91bootstrap generate the snapshot automatically.
    • Linux patch: fastboot-linux-based-on-linux4microchip-20XX.XX.patch

Snapshot Image Generation

A valid snapshot must be captured from a running Linux system and saved to Non-Volatile Memory (NVM) (like an SD™ card or NAND Flash) before ultra-fast boot; this is done by at91bootstrap when put in Restore mode.

Start the standard boot sequence from ROM boot.

Update U-Boot bootargs.

Verify that the kernel and applications are ready.

Enter BSR mode by typing “echo mem > /sys/power/state” (make sure that RESTORE is set as the mem argument).

DDR enters Self-refresh mode.

An automatic CPU reset is triggered.

The Read-Only Memory (ROM) boot sequence is starting.

The ROM code is executed and loads the at91bootstrap into the internal Static Random-Access Memory (SRAM).

Exit DDR Self Refresh.

Analyze MEM_MAP from kernel, to get a valid memory page.

Save the valid memory page (Snapshot of DRAM) to NVM.

Power off the system.

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Demo

This is a demo on the SAMA7D65 Curiosity board showing the Automatically Load and Save Snapshot Image feature.

Using Restore mode, at91bootstrap saves the current DDR memory contents—including the system state, kernel, and running applications—as a snapshot image in flash memory. On the next boot, the snapshot image is restored to DDR, allowing the system and applications to resume immediately while bypassing most of the traditional boot process.

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