meta-sunxi/README.md
Trevor Woerner d32866858f README.md: improve instructions for sunxi versions
If the user wants to build the sunxi version of the kernel they can specify
the PREFERRED_PROVIDER block in their conf/local.conf (i.e. they don't need to
edit the layer explicitly).

Also, now that gcc-5.2 is the default on master, inform the user how they can
continue to build the sunxi version (3.4%) version of the kernel by forcing
the compiler to version 4.9.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
2015-09-21 22:04:36 -04:00

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meta-sunxi
==============
Official sunxi OpenEmbedded layer for Allwinner-based boards.
This layer depends on the additional layer:
meta-openembedded: git://git.openembedded.org/meta-openembedded
Tested with core-image-base.
Maintainers:
* Nicolas Aguirre <aguirre.nicolas@gmail.com>
* Enrico Butera <ebutera@users.sourceforge.net>
* Sergey Lapin <slapin@ossfans.org>
Kernel / U-Boot Version
===========
Most Allwinner devices and hardware are supported in mainline kernel and U-Boot, so this layer builds mainline by default.
There is a custom U-Boot and Kernel version for sunxi devices which includes some special drivers not mainlined.
These versions are rather old (3.4 for kernel and 2014.04 for U-Boot), but may support more functions and devices than current mainline
If you want to switch back to sunxi versions for some reasons (no device tree available, unsupported hardware), either:
- change the file conf/machine/include/sunxi.inc to include the following block
- edit your conf/local.conf to add the following block
PREFERRED_PROVIDER_u-boot="u-boot-sunxi"
PREFERRED_PROVIDER_virtual/bootloader="u-boot-sunxi"
PREFERRED_PROVIDER_virtual/kernel="linux-sunxi"
If you already have built the mainline versions it might be necessary to reset the build directories with:
bitbake -c clean linux
bitbake -c clean u-boot
Also, older kernel versions such as this don't build successfully with any gcc version 5.0 or newer. Since gcc-5.2 is the current
default compiler on master, if you wish to build this kernel with master you'll need to add the following to your conf/local.conf:
GCCVERSION = "4.9%"
Performance
===========
The default machine settings are meant to be the lowest common denominator, maximizing generality.
Significantly better performance (2x-3x) can be achieved with the following settings:
**_Allwinner A20_**
For Allwinner A20 (Cubieboard2/CubieTruck), the following tuning options are recommended:
_Enable hardfloat, thumb2 and neon capabilities_
DEFAULTTUNE = "cortexa7hf-neon-vfpv4"
This tuning profile takes advantage of the Allwinner A20 hardfloat, neon and vfpv4 capabilities.
_Change CPU governor to ondemand, and tune settings_
echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
echo 336000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
echo 912000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
#More aggressive
#echo 1008000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
echo 40 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
echo 200000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate
This code changes the default CPU governor from _fantasy_ to _ondemand_, and tunes its settings, as recommended at http://linux-sunxi.org/Cpufreq
For additional discussion, see https://github.com/linux-sunxi/meta-sunxi/issues/25