X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=blobdiff_plain;f=docs%2FHowToBuildOnARM.rst;h=f2edaef76cd10e5333aca1e3a80b393de5925cfa;hp=793015a4ed40f7d97e161dfe0da8300878b1b235;hb=29e82393abf3d8f578c6719af03b596858761a4f;hpb=7149ef0176240ee5a09b0f6ad6300d1a966a31d1

diff --git a/docs/HowToBuildOnARM.rst b/docs/HowToBuildOnARM.rst
index 793015a4ed4..f2edaef76cd 100644
--- a/docs/HowToBuildOnARM.rst
+++ b/docs/HowToBuildOnARM.rst
@@ -1,34 +1,69 @@
-.. _how_to_build_on_arm:
-
-===================================================================
-How To Build On ARM
-===================================================================
-
-.. sectionauthor:: Wei-Ren Chen (陳韋任) <chenwj@iis.sinica.edu.tw>
-
-Introduction
-============
-
-This document contains information about building/testing LLVM and
-Clang on ARM.
-
-Notes On Building LLVM/Clang on ARM
-=====================================
-Here are some notes on building/testing LLVM/Clang on ARM. Note that
-ARM encompasses a wide variety of CPUs; this advice is primarily based
-on the ARMv6 and ARMv7 architectures and may be inapplicable to older chips.
-
-#. If you are building LLVM/Clang on an ARM board with 1G of memory or less,
-   please use ``gold`` rather then GNU ``ld``.
-   Building LLVM/Clang with ``--enable-optimized``
-   is prefered since it consumes less memory. Otherwise, the building
-   process will very likely fail due to insufficient memory. In any
-   case it is probably a good idea to set up a swap partition.
-
-#. If you want to run ``make
-   check-all`` after building LLVM/Clang, to avoid false alarms (eg, ARCMT
-   failure) please use the following configuration:
-
-   .. code-block:: bash
-
-     $ ../$LLVM_SRC_DIR/configure --with-abi=aapcs
+===================================================================
+How To Build On ARM
+===================================================================
+
+Introduction
+============
+
+This document contains information about building/testing LLVM and
+Clang on an ARM machine.
+
+This document is *NOT* tailored to help you cross-compile LLVM/Clang
+to ARM on another architecture, for example an x86_64 machine. To find
+out more about cross-compiling, please check :doc:`HowToCrossCompileLLVM`.
+
+Notes On Building LLVM/Clang on ARM
+=====================================
+Here are some notes on building/testing LLVM/Clang on ARM. Note that
+ARM encompasses a wide variety of CPUs; this advice is primarily based
+on the ARMv6 and ARMv7 architectures and may be inapplicable to older chips.
+
+#. If you are building LLVM/Clang on an ARM board with 1G of memory or less,
+   please use ``gold`` rather then GNU ``ld``.
+   Building LLVM/Clang with ``--enable-optimized``
+   is preferred since it consumes less memory. Otherwise, the building
+   process will very likely fail due to insufficient memory. In any
+   case it is probably a good idea to set up a swap partition.
+
+#. If you want to run ``make check-all`` after building LLVM/Clang, to avoid
+   false alarms (e.g., ARCMT failure) please use at least the following
+   configuration:
+
+   .. code-block:: bash
+
+     $ ../$LLVM_SRC_DIR/configure --with-abi=aapcs-vfp
+
+#. The most popular Linaro/Ubuntu OS's for ARM boards, e.g., the
+   Pandaboard, have become hard-float platforms. The following set
+   of configuration options appears to be a good choice for this
+   platform:
+
+   .. code-block:: bash
+
+     ./configure --build=armv7l-unknown-linux-gnueabihf \
+     --host=armv7l-unknown-linux-gnueabihf \
+     --target=armv7l-unknown-linux-gnueabihf --with-cpu=cortex-a9 \
+     --with-float=hard --with-abi=aapcs-vfp --with-fpu=neon \
+     --enable-targets=arm --enable-optimized --enable-assertions
+
+#. ARM development boards can be unstable and you may experience that cores
+   are disappearing, caches being flushed on every big.LITTLE switch, and
+   other similar issues.  To help ease the effect of this, set the Linux
+   scheduler to "performance" on **all** cores using this little script:
+
+   .. code-block:: bash
+
+      # The code below requires the package 'cpufrequtils' to be installed.
+      for ((cpu=0; cpu<`grep -c proc /proc/cpuinfo`; cpu++)); do
+          sudo cpufreq-set -c $cpu -g performance
+      done
+
+#. Running the build on SD cards is ok, but they are more prone to failures
+   than good quality USB sticks, and those are more prone to failures than
+   external hard-drives (those are also a lot faster). So, at least, you
+   should consider to buy a fast USB stick.  On systems with a fast eMMC,
+   that's a good option too.
+
+#. Make sure you have a decent power supply (dozens of dollars worth) that can
+   provide *at least* 4 amperes, this is especially important if you use USB
+   devices with your board.