Documentation: Add coreboot architecture
Describe the coreboot stages, given a short introduction what is done and add a chart for coreboot's vs EDK II bootflow as well as the source for the SVG. TODO: Describe stages in detail in a separate commit. Change-Id: I98cb61b1d0d29ac9d03f5ef3644d51a8e14bad74 Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com> Reviewed-on: https://review.coreboot.org/c/coreboot/+/32123 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net> Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
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# coreboot architecture
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## Overwiew
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![][architecture]
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[architecture]: comparision_coreboot_uefi.svg
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## Stages
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coreboot consists of multiple stages that are compiled as separate binaries and
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are inserted into the CBFS with custom compression. The bootblock usually doesn't
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have compression while the ramstage and payload are compressed with LZMA.
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Each stage loads the next stage a given address (possibly decompressing it).
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Some stages are relocatable and can be placed anywhere in DRAM. Those stages are
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usually cached in CBMEM for faster loading times on ACPI S3 resume.
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Supported stage compressions:
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* none
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* LZ4
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* LZMA
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## bootblock
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The bootblock is the first stage executed after CPU reset. It is written in
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assembly language and its main task is to set up everything for a C-environment:
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Common tasks:
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* Cache-As-RAM for heap and stack
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* Set stack pointer
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* Clear memory for BSS
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* Decompress and load the next stage
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On x86 platforms that includes:
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* Microcode updates
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* Timer init
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* Switching from 16-bit real-mode to 32-bit protected mode
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The bootblock loads the romstage or the verstage if verified boot is enabled.
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### Cache-As-Ram
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The *Cache-As-Ram*, also called Non-Eviction mode, or *CAR* allows to use the
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CPU cache like regular SRAM. This is particullary usefull for high level
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languages like `C`, which need RAM for heap and stack.
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The CAR needs to be activated using vendor specific CPU instructions.
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The following stages run when Cache-As-Ram is active:
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* bootblock
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* romstage
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* verstage
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* postcar
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## verstage
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The verstage is where the root-of-trust starts. It's assumed that
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it cannot be overwritten in-field (together with the public key) and
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it starts at the very beginning of the boot process.
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The verstage installs a hook to verify a file before it's loaded from
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CBFS or a partition before it's accessed.
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The verified boot mechanism allows trusted in-field firmware updates
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combined with a fail-safe recovery mode.
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## romstage
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The romstage initializes the DRAM and prepares everything for device init.
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Common tasks:
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* Early device init
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* DRAM init
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## postcar
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To leave the CAR setup and run code from regular DRAM the postcar-stage tears
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down CAR and loads the ramstage. Compared to other stages it's minimal in size.
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## ramstage
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The ramstage does the main device init:
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* PCI device init
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* On-chip device init
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* TPM init (if not done by verstage)
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* Graphics init (optional)
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* CPU init (like set up SMM)
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After initialization tables are written to inform the payload or operating system
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about the current hardware existance and state. That includes:
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* ACPI tables (x86 specific)
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* SMBIOS tables (x86 specific)
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* coreboot tables
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* devicetree updates (ARM specific)
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It also does hardware and firmware lockdown:
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* Write-protection of boot media
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* Lock security related registers
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* Lock SMM mode (x86 specific)
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## payload
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The payload is the software that is run after coreboot is done. It resides in
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the CBFS and there's no possibility to choose it at runtime.
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For more details have a look at [payloads](../payloads.md).
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN" "http://www.w3.org/TR/2001/PR-SVG-20010719/DTD/svg10.dtd">
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<svg width="55cm" height="28cm" viewBox="62 37 1088 559" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
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<text font-size="22.5778" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="482.342" y="58.1574">
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<tspan x="482.342" y="58.1574">Platform Initialization Firmware Phases</tspan>
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</text>
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<text font-size="16.9333" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="98.4514" y="435.714">
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<tspan x="98.4514" y="435.714">EDK II - stages</tspan>
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</text>
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<text font-size="12.8" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="1073.49" y="499.998">
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<tspan x="1073.49" y="499.998">time</tspan>
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</text>
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<text font-size="16.9333" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="82.8266" y="330.476">
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<tspan x="82.8266" y="330.476">coreboot - stages</tspan>
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</text>
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<g>
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<tspan x="315.718" y="434.72">Security</tspan>
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<tspan x="315.718" y="450.72">(SEC)</tspan>
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</text>
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<tspan x="524.384" y="427.181">Pre-EFI</tspan>
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<tspan x="524.384" y="443.181">Initialization Environment</tspan>
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<tspan x="524.384" y="459.181">(PEI)</tspan>
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<tspan x="802.649" y="427.717">Driver Execution</tspan>
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<tspan x="802.649" y="443.717">Environment</tspan>
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<tspan x="802.649" y="459.717">(DXE)</tspan>
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<g>
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<tspan x="1028.92" y="436.127">Boot Device Selection</tspan>
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<tspan x="1028.92" y="452.127">(BDS)</tspan>
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</text>
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</g>
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<g>
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<rect style="fill: #90c9ff" x="254.747" y="291.309" width="125.314" height="69.1471"/>
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<tspan x="317.404" y="329.782">bootblock</tspan>
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</text>
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</g>
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<g>
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<rect style="fill: #90c9ff" x="476.354" y="290.735" width="89.65" height="69.1471"/>
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<tspan x="521.179" y="329.209">romstage</tspan>
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</text>
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<g>
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<rect style="fill: #90c9ff" x="382.317" y="291.011" width="92.1" height="69.1471"/>
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<text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="428.367" y="321.485">
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<tspan x="428.367" y="321.485">verstage</tspan>
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<tspan x="428.367" y="337.485">(optional)</tspan>
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</text>
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<g>
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<text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="617.11" y="321.464">
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<tspan x="617.11" y="321.464">postcar</tspan>
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<tspan x="617.11" y="337.464">(x86 only)</tspan>
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</text>
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</g>
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<g>
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<tspan x="751.903" y="303.927">ramstage</tspan>
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</text>
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<g>
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<rect style="fill: #90c9ff" x="667.84" y="321.487" width="167.519" height="53"/>
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<text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="751.6" y="343.887">
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<tspan x="751.6" y="343.887">SMM</tspan>
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<tspan x="751.6" y="359.887">(x86 only)</tspan>
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</text>
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<g>
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<text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="1027.83" y="321.624">
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<tspan x="1027.83" y="321.624">payload</tspan>
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</text>
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<tspan x="294.462" y="226.578">Assembly</tspan>
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<tspan x="459.87" y="146.667">Cache-As-RAM</tspan>
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</text>
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</g>
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<g>
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<rect style="fill: #ff8484" x="506.676" y="159.67" width="599.421" height="27"/>
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<rect style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" x="506.676" y="159.67" width="599.421" height="27"/>
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<tspan x="806.387" y="177.07">DRAM</tspan>
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</text>
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</g>
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<text font-size="12.7998" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="387.045" y="241.637">
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<tspan x="387.045" y="241.637"></tspan>
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</text>
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<text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="646.853" y="226.783">
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<tspan x="646.853" y="226.783">C</tspan>
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</text>
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</g>
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<g>
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<text font-size="12.8" style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:700" x="752.5" y="256.312">
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<tspan x="752.5" y="256.312">ADA SPARK (x86 only)</tspan>
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</text>
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</g>
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<tspan x="84.2481" y="233.28">coreboot</tspan>
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<tspan x="84.2481" y="254.446">source languages</tspan>
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</text>
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<tspan x="86.5008" y="153.786">code/heap</tspan>
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<tspan x="86.5008" y="174.953">memory location </tspan>
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</text>
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<tspan x="888.733" y="304.363">BL31</tspan>
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<tspan x="888.733" y="320.363">(ARM only)</tspan>
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</text>
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</g>
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<text font-size="12.7998" style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal" x="209.772" y="508.772">
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<tspan x="209.772" y="508.772">Power on</tspan>
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</text>
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<path style="fill: none; fill-opacity:0; stroke-width: 1; stroke: #000000" d="M 955.029 209.941 C 967.678,210.1 946.349,230.772 955.598,237.021"/>
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</svg>
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After Width: | Height: | Size: 12 KiB |
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@ -1,5 +1,6 @@
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# Getting Started
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* [coreboot architecture](architecture.md)
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* [Build System](build_system.md)
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* [Submodules](submodules.md)
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* [Kconfig](kconfig.md)
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