ARM32 in Linux and Open Source Hardware Certification
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ARM32 Page Tables
As I continue to describe in different postings how the ARM32 start-up sequence works, it becomes necessary to explain in-depth the basic kernel concepts around page tables and how it is implemented on ARM32 platforms.
To understand the paging setup, we need to repeat and extend some Linux paging lingo. Some good background is to read Mel Gormans description of the Linux page tables from his book “Understanding the Linux Virtual Memory Manager”. This book was published in 2007 and is based on Mel’s PhD thesis from 2003. Some stuff has happened in the 13 years since then, but the basics still hold. It is necessary to also understand the new layers in the page tables such as the five layers of page tables currently used in the Linux kernel.
First a primer: the ARM32 architecture with a classic MMU has 2 levels of page tables and the more recent LPAE (Large Physical Address Extension) MMU has 3 levels of page tables.
Only some of the ARMv7 architectures have LPAE, and it is only conditionally enabled, i.e. the machines can also use the classic MMU if they want, they have both. It is not enabled by default on the multi_v7 configuration: your machine has to explicitly turn it on during compilation. The layout is so different that the same binary image can never support both classic and LPAE MMU in the same kernel image.
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Announcing the Open Source Hardware Certification API – Open Source Hardware Association
Today we are excited to announce the launch of a read/write API for our Open Source Hardware Certification program. This API will make it easier to apply for certification directly from where you already document your hardware, as well as empower research, visualizations, and explorations of currently certified hardware.
OSHWA’s Open Source Hardware Certification program has long been an easy way for creators and users alike to identify hardware that complies with the community definition of open source hardware. Since its creation in 2016, this free program has certified hardware from over 45 countries on every continent except Antarctica. Whenever you see the certification logo on hardware:
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