diff --git a/Documentation/getting_started/architecture.md b/Documentation/getting_started/architecture.md new file mode 100644 index 0000000000..6ef63594cf --- /dev/null +++ b/Documentation/getting_started/architecture.md @@ -0,0 +1,105 @@ +# coreboot architecture + +## Overwiew +![][architecture] + +[architecture]: comparision_coreboot_uefi.svg + +## Stages +coreboot consists of multiple stages that are compiled as separate binaries and +are inserted into the CBFS with custom compression. The bootblock usually doesn't +have compression while the ramstage and payload are compressed with LZMA. + +Each stage loads the next stage a given address (possibly decompressing it). + +Some stages are relocatable and can be placed anywhere in DRAM. Those stages are +usually cached in CBMEM for faster loading times on ACPI S3 resume. + +Supported stage compressions: +* none +* LZ4 +* LZMA + +## bootblock +The bootblock is the first stage executed after CPU reset. It is written in +assembly language and its main task is to set up everything for a C-environment: + +Common tasks: + +* Cache-As-RAM for heap and stack +* Set stack pointer +* Clear memory for BSS +* Decompress and load the next stage + +On x86 platforms that includes: + +* Microcode updates +* Timer init +* Switching from 16-bit real-mode to 32-bit protected mode + +The bootblock loads the romstage or the verstage if verified boot is enabled. + +### Cache-As-Ram +The *Cache-As-Ram*, also called Non-Eviction mode, or *CAR* allows to use the +CPU cache like regular SRAM. This is particullary usefull for high level +languages like `C`, which need RAM for heap and stack. + +The CAR needs to be activated using vendor specific CPU instructions. + +The following stages run when Cache-As-Ram is active: +* bootblock +* romstage +* verstage +* postcar + +## verstage +The verstage is where the root-of-trust starts. It's assumed that +it cannot be overwritten in-field (together with the public key) and +it starts at the very beginning of the boot process. +The verstage installs a hook to verify a file before it's loaded from +CBFS or a partition before it's accessed. + +The verified boot mechanism allows trusted in-field firmware updates +combined with a fail-safe recovery mode. + +## romstage +The romstage initializes the DRAM and prepares everything for device init. + +Common tasks: + +* Early device init +* DRAM init + +## postcar +To leave the CAR setup and run code from regular DRAM the postcar-stage tears +down CAR and loads the ramstage. Compared to other stages it's minimal in size. + +## ramstage + +The ramstage does the main device init: + +* PCI device init +* On-chip device init +* TPM init (if not done by verstage) +* Graphics init (optional) +* CPU init (like set up SMM) + +After initialization tables are written to inform the payload or operating system +about the current hardware existance and state. That includes: + +* ACPI tables (x86 specific) +* SMBIOS tables (x86 specific) +* coreboot tables +* devicetree updates (ARM specific) + +It also does hardware and firmware lockdown: +* Write-protection of boot media +* Lock security related registers +* Lock SMM mode (x86 specific) + +## payload +The payload is the software that is run after coreboot is done. It resides in +the CBFS and there's no possibility to choose it at runtime. + +For more details have a look at [payloads](../payloads.md). + diff --git a/Documentation/getting_started/comparision_coreboot_uefi.dia b/Documentation/getting_started/comparision_coreboot_uefi.dia new file mode 100644 index 0000000000..19c491fa7e Binary files /dev/null and b/Documentation/getting_started/comparision_coreboot_uefi.dia differ diff --git a/Documentation/getting_started/comparision_coreboot_uefi.svg b/Documentation/getting_started/comparision_coreboot_uefi.svg new file mode 100644 index 0000000000..3ea2fa6930 --- /dev/null +++ b/Documentation/getting_started/comparision_coreboot_uefi.svg @@ -0,0 +1,176 @@ + + + + + + + + + + + + + + Platform Initialization Firmware Phases + + + EDK II - stages + + + time + + + coreboot - stages + + + + + + Security + (SEC) + + + + + + + Pre-EFI + Initialization Environment + (PEI) + + + + + + + Driver Execution + Environment + (DXE) + + + + + + + Boot Device Selection + (BDS) + + + + + + + bootblock + + + + + + + romstage + + + + + + + verstage + (optional) + + + + + + + postcar + (x86 only) + + + + + + + ramstage + + + + + + + SMM + (x86 only) + + + + + + + payload + + + + + + + Assembly + + + + + + + Cache-As-RAM + + + + + + + DRAM + + + + + + + + + + + C + + + + + + + ADA SPARK (x86 only) + + + + coreboot + source languages + + + code/heap + memory location + + + + + + + + BL31 + (ARM only) + + + + Power on + + + + + + + diff --git a/Documentation/getting_started/index.md b/Documentation/getting_started/index.md index 8f2a58e1c5..52d873ece2 100644 --- a/Documentation/getting_started/index.md +++ b/Documentation/getting_started/index.md @@ -1,5 +1,6 @@ # Getting Started +* [coreboot architecture](architecture.md) * [Build System](build_system.md) * [Submodules](submodules.md) * [Kconfig](kconfig.md)