[OCaml] Don't build stub libraries twice.

[oota-llvm.git] / docs / HowToBuildOnARM.rst

diff --git a/docs/HowToBuildOnARM.rst b/docs/HowToBuildOnARM.rst
index 4e256395930e49dbb70a88e517fe0f15be1e76a2..f2edaef76cd10e5333aca1e3a80b393de5925cfa 100644 (file)
--- a/docs/HowToBuildOnARM.rst
+++ b/docs/HowToBuildOnARM.rst
@@ -1,5 +1,3 @@
-.. _how_to_build_on_arm:
-
 ===================================================================
 How To Build On ARM
 ===================================================================
@@ -8,7 +6,11 @@ Introduction
 ============
 
 This document contains information about building/testing LLVM and
-Clang on ARM.
+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
 =====================================
@@ -19,27 +21,49 @@ 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
+   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 (eg, ARCMT
-   failure) please use at least the following configuration:
+#. 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, eg, the
+#. 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 --disable-optimized --enable-assertions
+     ./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.