Architectures_embedded [FreeBSD WIKI]

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====== Embedded / Arch ======
http://tinyurl.com/yd5l4mak
https://hackmd.io/CwdgnAxghgrAzAEwLQAYBMKBsTgEYFhJhgCmESUCAHGAEa0wBmtcIjQA#

===== FreeBSD RISC-V Updates =====
{{DevSummit/201708/Architectures_embedded/DevSummit/201708/freebsd_riscv_updates.pdf?linkonly|RISC-V Update Slides}}

  * GENERIC kernel added August 2017
  * Updates for new Privileged Architecture (v1.10)
    * VM changes required to access userspace from supervisor (kernel)
    * Execute only pages not acceasable from kernel.  Unclear if this matters (Brooks: execute-only isn't practical with normal compilers and modern languages)
  * Testing with Compressed Extension (smaller instructions)
    * Compression ratio 1.19 vs 1.25 for micromips
  * Finally migrated to FDT

===== Open issues for arches =====
==== Arm ====
  * Work in progress on GENERIC kernel
  * Discussion is ongoing to add armv7 as a TARGET_ARCH (andrew@ thinks likely)
    * LLD currently supports only armv7 for 32-bit arm
==== Arm64 ====
  * andrew@ working NUMA support for dual package %%ThunderX%%
  * Single package %%ThunderX%% and %%SoftIron%% work
  * Raspberry-pi 3 works
  * 64-bit pi2 not yet working due to firmware
  * Most systems work with a GENERIC kernel
  * %%ThunderX%% in the cluster to build packages
  * %%ThunderX2%% on the way, but completely different hardware so may need considerable work
  * Ed started working on bringing up [[https://www.hardkernel.com/shop/odroid-c2/|ODROID C2]]
  * Would be useful to have a status chart listing what works on what platforms
==== Mips(64) ====
  * external toolchain with clang and lld mostly working
  * hardfloat target arches added by br@, probalby need more testing and package builds
  * Tests largely work, but some racey issues
  * br@ tried micromips builds.  Compilation works, but some work required on exception handlers.
==== PPC ====
  * No users present
==== Sparc64 ====
  * No modern processors supported
  * No modern clang support.  Will need to test external GCC or remove.
  * Unclear if a decent emulator exists.  What is qemu status for sun4u? ([[/MarkLinimon|MarkLinimon]] adds later: running qemu-sparc64 on amd64 merely hangs.)
===== Toolchains =====
  * Switching to builtin clang or external GCC for all architectures
  * Tier 1 likely to require in-tree premissively licensed toolchain
    * Still lacking a KLLDB
  * Need to pick a toolchain file for targets with out of tree toolchains
===== Tuning =====
  * Need to do more if we're going to handle (e.g) MIPS 24k APs and netflix 100+Gbps per host systems
    * Don't want a zillion knobs
    * Perhaps big vs small
      * Maybe in per arch std.FOO files?
      * Consider default file of nooptions, nodevice for tiny systems
      * Warner's minimal kernel project may also help
===== Packaging, release, distribution, usability =====
  * For RPi we would benefit from device tree overlays.
    * What is the status?
    * Need loader support?
  * It would be nice if we had compatible python interfaces to our SPI, I2C, GPIO interfaces
    * Really does need to just work with existing examples
    * Ed reports that basic stuff does work
  * Ed's coop student looking into adding %%FreeBSD%% to noobs ([[https://www.raspberrypi.org/downloads/noobs/]])
    * Current RPi boot process makes it hard to integrate %%FreeBSD%%
    * Requires uboot changes to work well.  In particular, need a way to tell uboot where it was loaded from.
===== Virtualization =====
  * Work in progress on bhyve for arm and arm64, Andy is currently reviewing patches
  * Power9 has extensions, but no easy way to access
  * Most recent MIPS versions support, but no access to hardware currently
===== Emulation =====
  * Tier 1 and probably 2 should have QEMU