# Cold boot architecture

Source: [https://docs.qualcomm.com/doc/80-70014-4/topic/bootloader-architecture.html](https://docs.qualcomm.com/doc/80-70014-4/topic/bootloader-architecture.html)

A cold boot starts the system from a power-off state. This process begins with the
            [PBL](https://docs.qualcomm.com/doc/80-70014-4/topic/bootloader.html#bootloader__section_gs4_mxh_rzb).

The following figure shows the cold boot flow:
Figure : Cold boot flow
                
                ![](data:image/png;base64,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)

The cold boot process operates in two security modes: Secure and Nonsecure.

At the EL0, EL1, and EL2 [exception levels](https://developer.arm.com/documentation/102412/0103/Privilege-and-Exception-levels/Exception-levels), the boot core can operate in
            either Secure or Nonsecure mode while EL3 always operates in Secure mode.

For more information on the security modes, see [Software Security Architecture](https://docs.qualcomm.com/bundle/publicresource/topics/80-70015-11/architecture.html).

The Linux kernel runs in the Nonsecure EL1 state. After the security settings are
            completed in the secure EL3 state, the XBL may switch to the UEFI nonsecure EL1
            state.

The cold boot sequence involves the following steps:

1. After a reset, the boot core exits the Reset state and executes the PBL. The PBL
                initializes the hardware clocks, CPU caches, memory management unit (MMU), and
                identifies the boot device based on the boot option settings.
2. The PBL loads and authenticates the XBL from the boot device. The XBL runs the
                security setup in EL3 Secure state and performs the following tasks:
    1. Initializes the hardware, firmware images, CPU cache, MMU, boot device,
                        PMIC, and DDR.
    2. Loads and authenticates the Qualcomm TEE image from the boot device.
    3. Loads and authenticates the Qualcomm Hypervisor image.
    4. Loads and authenticates the UEFI image.
    5. Makes a secure channel manager (SCM) call to jump to the Qualcomm TEE image.
                        SCM is the driver that communicates with Qualcomm TEE using a [secure monitor call](https://developer.arm.com/documentation/ddi0333/latest/programmer-s-model/exceptions/secure-monitor-call--smc-) (SMC).
3. The Qualcomm TEE sets up the secure environment and runs the Qualcomm Hypervisor
                image.
4. The Qualcomm Hypervisor hands over control to UEFI, which then loads and
                    authenticates the systemd-boot EFI image using the [UEFI secure boot](https://docs.qualcomm.com/bundle/publicresource/topics/80-70015-11/enable-uefi-secure-boot.html).
5. The systemd-boot image loads and authenticates the Qualcomm Linux kernel image, and
                then passes control to the Qualcomm Linux kernel.
6. The Qualcomm Linux kernel launches various Linux applications such as the bash
                shell.

**Parent Topic:** [Architecture](https://docs.qualcomm.com/doc/80-70014-4/topic/architecture.html)

Last Published: Feb 02, 2026

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