draft chapter on boot environments

Signed-off-by: Daniel Maslowski <[email protected]>

Author: orangecms

src/SUMMARY.md

@@ -1,4 +1,5 @@
 [PSI Spec Introduction](intro.md)
 [Mask ROMs and Loaders](mask-roms-loaders.md)
 [Platform Initialization](platform-initialization.md)
+[Boot Environments](boot-environments.md)
 [Platform Security](platform-security.md)

src/boot-environments.md

@@ -0,0 +1,25 @@
+## Boot Environments
+
+A _boot environment_ is the hosting system of a _boot loader_.
+
+Boot processes may be interactive, or automatic, or static, set up in many ways.
+
+The following table classifies various approaches with example implementations.
+
+|             | serial       | network         | graphics               |
+| ----------- | ------------ | --------------- | ---------------------- |
+| Automatic   | xmodem       | TFTP, HTTP, PXE | splash screen          |
+| Interactive | shell, ReGIS | `cpu`, web      | framebuffer, text menu |
+
+A boot environment may be configurable. Configuration may be changed at runtime,
+out of band, or at build time depending on the use case.
+
+The following is a list of examples.
+
+- [U-Boot configuration](https://docs.u-boot.org/en/latest/develop/distro.html)
+- [UEFI NVRAM](https://uefi.org/specs/UEFI/2.10/03_Boot_Manager.html)
+- [SeaBIOS (e.g., coreboot NVRAM)](https://www.seabios.org/Runtime_config)
+- [Boot Loader Specification](https://uapi-group.org/specifications/specs/configuration_files_specification/)
+- [GRUB configuration](https://www.gnu.org/software/grub/manual/grub/html_node/Configuration.html)
+- [syslinux/extlinux configuration files](https://wiki.syslinux.org/wiki/index.php?title=SYSLINUX)
+- [PXE scripting/menu](https://ipxe.org/)