Diff for /wikisrc/ports/evbarm.mdwn between versions 1.57 and 1.65

version 1.57, 2018/11/21 13:27:04 version 1.65, 2018/11/24 16:22:20
Line 29  four main variables: the word size, the  Line 29  four main variables: the word size, the 
 endianness, and whether there is hardware floating point.  By default  endianness, and whether there is hardware floating point.  By default
 the CPU type is "earm", and this implies aarch32 (32-bit), \todo cpu  the CPU type is "earm", and this implies aarch32 (32-bit), \todo cpu
 architecture, little endian (el when explicitly stated), and soft  architecture, little endian (el when explicitly stated), and soft
 (emulated) floating point.  Another example, suitable for Raspberry PI  (Emulated) floating point.  Another example, suitable for Raspberry PI
 2, is earmv7hf, which is aarch32, the v7 instruction set, little  2, is earmv7hf, which is aarch32, the v7 instruction set, little
 endian, and hardware floating point.  endian, and hardware floating point.
   
Line 46  sometimes referred to as a distinct port Line 46  sometimes referred to as a distinct port
 with code in src/sys/arch/aarch64, but it is built as the evbarm port  with code in src/sys/arch/aarch64, but it is built as the evbarm port
 with aarch64 cpu type, and available as the alias evbarm64.  with aarch64 cpu type, and available as the alias evbarm64.
   
   Note that MACHINE_ARCH=aarch64 currently refers to the A64 instruction
   set and the aarch64 architecture, built for the armv8 architecture.
   (Note also that armv8 is the first architecture to support aarch64, so
   this will not be an issue until at least armv9.)
   
   #### ABI types
   
   There are two basic ABIs on ARM.  One, called oabi, assumed a
   particular kind of hardware floating point (FPA).  This results in
   faulting any floating-point instructions for kernel emulation on a
   vast number of CPus, which is very slow.  A newer one, called eabi,
   has two variants.  Both have stricter alignment rules, tending to 8
   byte rather than 4 bytes for 8-byte types (but actually read the specs
   if you care).  The one without "hf" emulates floating point without
   causing traps/emulation, and "hf" uses VFP instructions, which are
   present on modern CPUs. See the
   [TS-7200](https://wiki.embeddedarm.com/wiki/EABI_vs_OABI) and
   [Debian](https://wiki.debian.org/ArmEabiPort) documentation.
   
   Now, EABI is normal, and OABI is crufty.  The only real reason NetBSD
   retains OABI support is binary compatibility with older releases.  The
   "arm" and "armeb" MACHINE_ARCH targets are OABI; the rest of the
   targets, all having "earm" are EABI.
   
   \todo CHECK THIS: The "aarch64" MACHINE_ARCH target is an EABI variant.
   
   ### Relationship of MACHINE_ARCH to official ARM terminology
   
   Note that these are all little endian, and have big endian variants
   with a "eb" suffix.   
   
   [[!table data=<<EOT
   MACHINE_ARCH |bits | ARM architecture version            |ABI
   arm          |32   |?                                    |oabi
   earm         |32   |armv4 (effectively an alias)         |eabi
   earmv4       |32   |armv4 (no thumb, so ok on strongarm) |eabi
   earmv5       |32   |armv5t                               |eabi
   earmv6       |32   |armv6                                |eabi
   earmv7       |32   |armv7                                |eabi
   aarch64      |64   |armv8                                |\todo ? eabi
   EOT]]
   
   \todo Explain why, if we have armv4, and this is confusing, we still have earm as a MACHINE_ARCH.
   
   \todo Explain why aarch64 is a MACHINE_ARCH, when it seems like it
   should be something like armv8hf_64.
   
   \todo Explain if MACHINE_ARCH values correspond to a particular
   argument to some CPU selection command in gcc (and/or clang).
   
 ### Kernels and userland  ### Kernels and userland
   
 The evbarm userland can be used on any system that can run code of the  The evbarm userland can be used on any system that can run code of the

Removed from v.1.57  
changed lines
  Added in v.1.65


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