Registered User m (→Overview) |
Registered User mNo edit summary |
||
(67 intermediate revisions by 8 users not shown) | |||
Line 1: | Line 1: | ||
{{ApplicableFor | |||
{{ | |MPUs list=STM32MP13x, STM32MP15x | ||
|MPUs checklist=STM32MP13x, STM32MP15x | |||
}} | |||
__FORCETOC__ | __FORCETOC__ | ||
== Generic boot sequence == | == Generic boot sequence == | ||
=== Linux start-up === | === Linux start-up === | ||
Starting Linux<sup>®</sup> on a processor is done in several steps that progressively initialize the platform peripherals and memories. | Starting Linux<sup>®</sup> on a processor is done in several steps that progressively initialize the platform peripherals and memories. These steps are | ||
explained in the following | explained in the following paragraphs and illustrated by the diagram on the right, which also gives typical memory sizes for each stage. | ||
[[File: Boot_chains_overview.png| | [[File: Boot_chains_overview.png|center|link=|Generic Linux boot chain]] | ||
==== ROM code ==== | ==== ROM code ==== | ||
The ROM code is a piece of software that takes its name from the read only memory (ROM) where it is stored. It fits in a few tens of Kbytes and maps its data in embedded RAM. It is the first code executed by the processor, and it embeds all the logic needed to select the boot device (serial link or | The ROM code is a piece of software that takes its name from the read only memory (ROM) where it is stored. It fits in a few tens of Kbytes and maps its data in embedded RAM. It is the first code executed by the processor, and it embeds all the logic needed to select the boot device (serial link or flash) from which the first-stage bootloader (FSBL) is loaded to the embedded RAM.<br> | ||
Most products require to trust the application that is running on the device and the ROM code is the first link in the chain of trust that must be established across all started components: this trust is established by authenticating the FSBL before starting it. In turn, the FSBL and each following component authenticates the next one, up to a level defined by the product manufacturer. | |||
==== First stage | ==== First stage bootloader (FSBL) ==== | ||
Among other things, the first stage | Among other things, the first stage bootloader (FSBL) initializes (part of) the clock tree and the external RAM controller. Finally, the FSBL loads the second-stage bootloader (SSBL) into the external RAM and jumps to it.<br /> | ||
The [[TF-A overview|Trusted Firmware-A (TF-A)]] and [[U-Boot overview|U-Boot]] secondary program loader (U-Boot SPL) are two possible FSBLs. | The [[TF-A overview|Trusted Firmware-A (TF-A)]] and [[U-Boot overview|U-Boot]] secondary program loader (U-Boot SPL) are two possible FSBLs. | ||
==== Second-stage | ==== Second-stage bootloader (SSBL) ==== | ||
The second-stage | The second-stage bootloader (SSBL) runs in a wide RAM so it can implement complex features (such as, USB, Ethernet, display), that are very useful to make Linux kernel loading more flexible (from a storage device on USB or on a network), and user-friendly (by showing a splash screen to the user). [[U-Boot overview|U-Boot]] is commonly used as a Linux bootloader in embedded systems. | ||
==== Linux kernel space ==== | ==== Linux kernel space ==== | ||
Line 27: | Line 26: | ||
==== Linux user space ==== | ==== Linux user space ==== | ||
Finally, the Linux kernel hands control to the user space starting the init process that runs all initialization actions described in the root file system (rootfs), including the application framework that exposes the user interface (UI) to the user<br /> | Finally, the Linux kernel hands control to the user space starting the init process that runs all initialization actions described in the root file system (rootfs), including the application framework that exposes the user interface (UI) to the user.<br /> | ||
=== Other services start-up === | === Other services start-up === | ||
[[File: STM32MP boot chain.png | [[File: STM32MP boot chain.png|right|link=|STM32MP boot chain]] | ||
In addition to <span style="color:#FFFFFF; background: | In addition to <span style="color:#FFFFFF; background:{{STDarkBlue}};"> Linux </span> startup, the boot chain also installs the secure monitor and may support coprocessor firmware loading. | ||
<br /><br /> | <br /><br /> | ||
For instance, for the STM32MP15, the boot chain starts: | For instance, for the STM32MP15, the boot chain starts: | ||
* | * The <span style="color:#FFFFFF; background:{{STPink}};"> secure monitor </span>, supported by the Arm<sup>®</sup> Cortex<sup>®</sup>-A secure context (TrustZone). Examples of use of a secure monitor are: user authentication, key storage, and tampering management. | ||
* | * The <span style="color:#FFFFFF; background:{{STLightBlue}};"> coprocessor </span> firmware, running on the Arm Cortex-M core. This can be used to offload real-time or low-power services. | ||
<br /> | <br /> | ||
The dotted lines in the diagram on the right mean that: | The dotted lines in the diagram on the right mean that: | ||
* | * The <span style="color:#FFFFFF; background:{{STLightBlue}};"> coprocessor </span> can be started by the '''second stage bootloader (SSBL)''', known as “'''early boot'''”, or '''Linux kernel''' (by default). | ||
<br clear=all> | <br clear=all> | ||
== STM32MP boot sequence == | == STM32MP boot sequence == | ||
=== Diagram frames and legend === | === Diagram frames and legend === | ||
[[File:Boot diagrams contexts.png | [[File:Boot diagrams contexts.png|right|link=|STM32MP hardware execution contexts]] | ||
The [[Getting_started_with_STM32_MPU_devices#Multiple-core_architecture_concepts|hardware execution contexts]] are shown with vertical frames in the boot diagrams: | The [[Getting_started_with_STM32_MPU_devices#Multiple-core_architecture_concepts|hardware execution contexts]] are shown with vertical frames in the boot diagrams: | ||
* the <span style="color:#FFFFFF; background: | * the <span style="color:#FFFFFF; background:{{STPink}};"> Arm Cortex-A secure </span> context, in pink | ||
* the <span style="color:#FFFFFF; background: | * the <span style="color:#FFFFFF; background:{{STDarkBlue}};"> Arm Cortex-A non-secure </span> context, in dark blue | ||
* the <span style="color:#FFFFFF; background: | * the <span style="color:#FFFFFF; background:{{STLightBlue}};"> Arm Cortex-M </span> context, in light blue, for {{MicroprocessorDevice | device=15}} only | ||
The horizontal frame in: | The horizontal frame in: | ||
* the bottom part shows the '''boot chain''' | * the bottom part shows the '''boot chain''' | ||
* the top part shows the '''runtime''' services, that are installed by the '''boot chain''' | * the top part shows the '''runtime''' services, that are installed by the '''boot chain''' | ||
<br clear=all> | <br clear=all> | ||
[[File:Boot chains legend.png | [[File:Boot chains legend.png|right|link=|Boot chain diagrams legend]] | ||
The legend on the right | The legend on the right illustrates how the information about the various components shown in the frames are involved in the boot process. These are highlighted as follows: | ||
* The box '''color''' shows the component source code origin | * The box '''color''' shows the component source code origin | ||
* The '''arrows''' show the loading and calling actions between the components | * The '''arrows''' show the loading and calling actions between the components | ||
Line 62: | Line 60: | ||
<br clear=all> | <br clear=all> | ||
=== | === STM32MP13 boot chain === | ||
==== Overview ==== | ==== Overview ==== | ||
STM32MP13 boot chain uses [[TF-A overview|Trusted Firmware-A (TF-A)]] as the FSBL in order to fulfill all the requirements for security-sensitive customers, and it uses [[U-Boot overview|U-Boot]] as the SSBL. Note that this boot chain can run on any STM32MP13 device [[STM32MP13_microprocessor#Part_number_codification|security]] variant (that is, with or without the secure boot).<br> | |||
Refer to the [[Security overview|security overview]] for an introduction of the secure features available on STM32MP13, from the secure boot up to trusted applications execution. | |||
[[File:STM32MP13 boot chain.png|center|link=|STM32MP13 boot chain]] | |||
==== ROM code ==== | |||
The [[STM32 MPU ROM code overview|ROM code]] starts the processor in secure mode. It supports the FSBL authentication and decryption. | |||
==== First stage bootloader (FSBL) ==== | |||
The FSBL is executed from the [[SYSRAM_internal_memory|SYSRAM]].<br /> | |||
Among other things, this bootloader initializes (part of) the clock tree and the [[DDRCTRL and DDRPHYC internal peripherals|DDR controller]]. Finally, the FSBL loads the second-stage bootloader (SSBL) into the DDR external RAM and jumps to it.<br> | |||
The bootloader stage 2, so called TF-A BL2, is the [[TF-A overview|Trusted Firmware-A (TF-A)]] binary used as FSBL on STM32MP13.<br> | |||
==== Second stage bootloader (SSBL) ==== | |||
[[U-Boot overview|U-Boot]] is commonly used as a bootloader in embedded software and it is the one used on STM32MP13. | |||
==== Linux ==== | |||
Linux<sup>®</sup> OS is loaded in DDR by U-Boot and executed in the non-secure context. | |||
==== Secure OS / Secure monitor ==== | |||
The Cortex-A7 secure world supports [[OP-TEE overview|OP-TEE]] secure OS. | |||
=== STM32MP15 boot chain === | |||
==== Overview ==== | |||
STM32MP15 boot chain uses [[TF-A overview|Trusted Firmware-A (TF-A)]] as the FSBL in order to fulfill all the requirements for security-sensitive customers, and it uses [[U-Boot overview|U-Boot]] as the SSBL. Note that the authentication is optional with this boot chain, so it can run on any STM32MP15 device [[STM32MP15_microprocessor#Part_number_codification|security]] variant (that is, with or without the Secure boot).<br> | |||
[[ | Refer to the [[Security overview|security overview]] for an introduction of the secure features available on STM32MP15, from the secure boot up to trusted applications execution. | ||
<br> | [[File:Trusted boot chain.png|center|link=|STM32MP15 boot chain]] | ||
[[File: | Note: | ||
* The STM32MP15 coprocessor can be started at the SSBL level by the [[U-Boot overview|U-Boot early boot]] feature or, later, by the [[Linux remoteproc framework overview|Linux remoteproc framework]], depending on the application startup time-targets. | |||
* The | |||
==== ROM code ==== | |||
The [[ | The [[STM32 MPU ROM code overview|ROM code]] starts the processor in secure mode. It supports the FSBL authentication and offers authentication services to the FSBL. | ||
==== First stage bootloader (FSBL) ==== | |||
The FSBL is executed from the [[SYSRAM_internal_memory|SYSRAM]].<br /> | The FSBL is executed from the [[SYSRAM_internal_memory|SYSRAM]].<br /> | ||
Among other things, this | Among other things, this bootloader initializes (part of) the clock tree and the [[DDRCTRL and DDRPHYC internal peripherals|DDR controller]]. Finally, the FSBL loads the second-stage bootloader (SSBL) into the DDR external RAM and jumps to it.<br> | ||
The [[TF-A overview|Trusted Firmware-A (TF-A)]] | The bootloader stage 2, so called TF-A BL2, is the [[TF-A overview|Trusted Firmware-A (TF-A)]] binary used as FSBL on STM32MP15.<br> | ||
==== Second stage bootloader (SSBL) ==== | |||
[[U-Boot overview|U-Boot]] is commonly used as a bootloader in embedded software and it is the one used on STM32MP15. | |||
[[U-Boot overview|U-Boot]] is commonly used as a bootloader in embedded software. | |||
==== Linux ==== | |||
Linux<sup>®</sup> | Linux<sup>®</sup> OS is loaded in DDR by U-Boot and executed in the non-secure context. | ||
==== Secure OS / Secure monitor ==== | |||
The Cortex-A7 secure world can implement a minimal secure monitor (from [[TF-A_overview#BL32|TF-A]] or [[U-Boot overview|U-Boot]]) or a real secure OS, such as [[OP-TEE overview|OP-TEE]]. | The Cortex-A7 secure world can implement a minimal secure monitor (from [[TF-A_overview#BL32|TF-A SP-MIN]] or [[U-Boot overview|U-Boot]]) or a real secure OS, such as [[OP-TEE overview|OP-TEE]]. | ||
==== Coprocessor firmware ==== | |||
The coprocessor [[STM32CubeMP1 architecture|STM32Cube]] firmware can be started at the SSBL level by [[U-Boot overview|U-Boot]] with the remoteproc feature (rproc command) or, later, by [[Linux remoteproc framework overview|Linux remoteproc framework]], depending on the application startup time targets. | The coprocessor [[STM32CubeMP1 architecture|STM32Cube]] firmware can be started at the SSBL level by [[U-Boot overview|U-Boot]] with the remoteproc feature (rproc command) or, later, by [[Linux remoteproc framework overview|Linux remoteproc framework]], depending on the application startup time-targets. | ||
<noinclude> | |||
[[Category:Platform boot|0]] | |||
{{PublicationRequestId |22726 | 2022-03-03| previous : 13223 - 2019-09-11}} | |||
</noinclude> |
Revision as of 17:59, 16 March 2022
1. Generic boot sequence[edit | edit source]
1.1. Linux start-up[edit | edit source]
Starting Linux® on a processor is done in several steps that progressively initialize the platform peripherals and memories. These steps are explained in the following paragraphs and illustrated by the diagram on the right, which also gives typical memory sizes for each stage.

1.1.1. ROM code[edit | edit source]
The ROM code is a piece of software that takes its name from the read only memory (ROM) where it is stored. It fits in a few tens of Kbytes and maps its data in embedded RAM. It is the first code executed by the processor, and it embeds all the logic needed to select the boot device (serial link or flash) from which the first-stage bootloader (FSBL) is loaded to the embedded RAM.
Most products require to trust the application that is running on the device and the ROM code is the first link in the chain of trust that must be established across all started components: this trust is established by authenticating the FSBL before starting it. In turn, the FSBL and each following component authenticates the next one, up to a level defined by the product manufacturer.
1.1.2. First stage bootloader (FSBL)[edit | edit source]
Among other things, the first stage bootloader (FSBL) initializes (part of) the clock tree and the external RAM controller. Finally, the FSBL loads the second-stage bootloader (SSBL) into the external RAM and jumps to it.
The Trusted Firmware-A (TF-A) and U-Boot secondary program loader (U-Boot SPL) are two possible FSBLs.
1.1.3. Second-stage bootloader (SSBL)[edit | edit source]
The second-stage bootloader (SSBL) runs in a wide RAM so it can implement complex features (such as, USB, Ethernet, display), that are very useful to make Linux kernel loading more flexible (from a storage device on USB or on a network), and user-friendly (by showing a splash screen to the user). U-Boot is commonly used as a Linux bootloader in embedded systems.
1.1.4. Linux kernel space[edit | edit source]
The Linux kernel is started in the external memory and it initializes all the peripheral drivers that are needed on the platform.
1.1.5. Linux user space[edit | edit source]
Finally, the Linux kernel hands control to the user space starting the init process that runs all initialization actions described in the root file system (rootfs), including the application framework that exposes the user interface (UI) to the user.
1.2. Other services start-up[edit | edit source]

In addition to Linux startup, the boot chain also installs the secure monitor and may support coprocessor firmware loading.
For instance, for the STM32MP15, the boot chain starts:
- The secure monitor , supported by the Arm® Cortex®-A secure context (TrustZone). Examples of use of a secure monitor are: user authentication, key storage, and tampering management.
- The coprocessor firmware, running on the Arm Cortex-M core. This can be used to offload real-time or low-power services.
The dotted lines in the diagram on the right mean that:
- The coprocessor can be started by the second stage bootloader (SSBL), known as “early boot”, or Linux kernel (by default).
2. STM32MP boot sequence[edit | edit source]
2.1. Diagram frames and legend[edit | edit source]

The hardware execution contexts are shown with vertical frames in the boot diagrams:
- the Arm Cortex-A secure context, in pink
- the Arm Cortex-A non-secure context, in dark blue
- the Arm Cortex-M context, in light blue, for STM32MP15x lines
only
The horizontal frame in:
- the bottom part shows the boot chain
- the top part shows the runtime services, that are installed by the boot chain

The legend on the right illustrates how the information about the various components shown in the frames are involved in the boot process. These are highlighted as follows:
- The box color shows the component source code origin
- The arrows show the loading and calling actions between the components
- The Cube logo is used on the top right corner of components that can be configured via STM32CubeMX
- The lock show the components that can be authenticated during the boot process
2.2. STM32MP13 boot chain[edit | edit source]
2.2.1. Overview[edit | edit source]
STM32MP13 boot chain uses Trusted Firmware-A (TF-A) as the FSBL in order to fulfill all the requirements for security-sensitive customers, and it uses U-Boot as the SSBL. Note that this boot chain can run on any STM32MP13 device security variant (that is, with or without the secure boot).
Refer to the security overview for an introduction of the secure features available on STM32MP13, from the secure boot up to trusted applications execution.

2.2.2. ROM code[edit | edit source]
The ROM code starts the processor in secure mode. It supports the FSBL authentication and decryption.
2.2.3. First stage bootloader (FSBL)[edit | edit source]
The FSBL is executed from the SYSRAM.
Among other things, this bootloader initializes (part of) the clock tree and the DDR controller. Finally, the FSBL loads the second-stage bootloader (SSBL) into the DDR external RAM and jumps to it.
The bootloader stage 2, so called TF-A BL2, is the Trusted Firmware-A (TF-A) binary used as FSBL on STM32MP13.
2.2.4. Second stage bootloader (SSBL)[edit | edit source]
U-Boot is commonly used as a bootloader in embedded software and it is the one used on STM32MP13.
2.2.5. Linux[edit | edit source]
Linux® OS is loaded in DDR by U-Boot and executed in the non-secure context.
2.2.6. Secure OS / Secure monitor[edit | edit source]
The Cortex-A7 secure world supports OP-TEE secure OS.
2.3. STM32MP15 boot chain[edit | edit source]
2.3.1. Overview[edit | edit source]
STM32MP15 boot chain uses Trusted Firmware-A (TF-A) as the FSBL in order to fulfill all the requirements for security-sensitive customers, and it uses U-Boot as the SSBL. Note that the authentication is optional with this boot chain, so it can run on any STM32MP15 device security variant (that is, with or without the Secure boot).
Refer to the security overview for an introduction of the secure features available on STM32MP15, from the secure boot up to trusted applications execution.

Note:
- The STM32MP15 coprocessor can be started at the SSBL level by the U-Boot early boot feature or, later, by the Linux remoteproc framework, depending on the application startup time-targets.
2.3.2. ROM code[edit | edit source]
The ROM code starts the processor in secure mode. It supports the FSBL authentication and offers authentication services to the FSBL.
2.3.3. First stage bootloader (FSBL)[edit | edit source]
The FSBL is executed from the SYSRAM.
Among other things, this bootloader initializes (part of) the clock tree and the DDR controller. Finally, the FSBL loads the second-stage bootloader (SSBL) into the DDR external RAM and jumps to it.
The bootloader stage 2, so called TF-A BL2, is the Trusted Firmware-A (TF-A) binary used as FSBL on STM32MP15.
2.3.4. Second stage bootloader (SSBL)[edit | edit source]
U-Boot is commonly used as a bootloader in embedded software and it is the one used on STM32MP15.
2.3.5. Linux[edit | edit source]
Linux® OS is loaded in DDR by U-Boot and executed in the non-secure context.
2.3.6. Secure OS / Secure monitor[edit | edit source]
The Cortex-A7 secure world can implement a minimal secure monitor (from TF-A SP-MIN or U-Boot) or a real secure OS, such as OP-TEE.
2.3.7. Coprocessor firmware[edit | edit source]
The coprocessor STM32Cube firmware can be started at the SSBL level by U-Boot with the remoteproc feature (rproc command) or, later, by Linux remoteproc framework, depending on the application startup time-targets.