Building Qt to make use of the Beagle board’s SGX GPU

Introduction

Texas Instruments has a wiki which documents what is required to bring Qt
up on the Beagle board with full OpenGL ES (1/2) support:

http://www.tiexpressdsp.com/index.php/Building_Qt

and I would like to thank one of their engineers, Varun, for his quick turn
around times in addressing any questions I raised.

This blog entry is intended to serve a similar purpose, but is more verbose regarding
Qt considerations and the initial beagle board bring up. It attempts to serve
as a comprehensive independent source of information on getting Qt built
for the Beagle board with full OpenGL ES 2 support.

These instructions are intended for use with Qt 4.6 (and beyond), so grab
the release candidate or check Qt 4.6 out from the public git repository prior
to proceeding.

You can choose to use either Qt/Embedded or Qt/X11, both can
be successfully integrated with the Beagle board's SGX GPU and the only
point of divergence in these instructions will be at (Qt) configure time
and the client side system (run time) configuration. Both implementations
offer window management, via QWS and X11 respectively, and operate at
around 27fps and 22fps respectively when running our hellogl_es2 example.
(16bit color depth at 1280x720)

I personally deploy Ångström on my Beagle board, it handles a large amount
of the logistics surrounding cross compilation and is generally very
agreeable, and these instructions are therefore going to be bolted to
Ångström for completeness. Feel free to establish an environment capable of
showing the OpenGL ES examples TI provide, then following the Qt level
considerations (Configuring Qt) accordingly.

For those holding a dormant Beagle board who are open to the author's
distribution preferences:

Building the Ångström rootfs

Open Embedded is manifested in a git repository: in this posting we are
working within origin/stable/2009. Please follow the instructions give
here, they are comprehensive and got me completely off the ground.

http://www.angstrom-distribution.org/building-angstrom

These instructions end in you running:

bitbake base-image ; bitbake console-image ; bitbake x11-image

which actually builds an X11 angstrom image for your Beagle board. Please
note, you will need to build the X11-image if you want to build and deploy
the SGX packages (we will do this in the next section) via Ångström as opkg considers
X11 to be a required dependency of libgles-omap3_3.00.00.09. This is due
to one of the encapsulated windowing system libraries being X11 centric:

libpvrPVR2D_X11WSEGL.so

Regardless of the indicated X11 dependency, this package will bestow the required
kernel module on you for general OpenGL ES usage (console or X11). We will be
building our own QWS centric (libpvrPVR2D_X11WSEGL.so equivalent) library
behind the scenes for QWS in the Qt/Embedded instructions given later.

Ångström SGX integration

You now need to integrate the SGX drivers on your Ångström system.

You need to get your paws on:

OMAP35x_Graphics_SDK_setuplinux_3_00_00_09.bin

with the following MD5 checksum:

e15147ad76ddbe7c5aec682f5455b774

Getting this involves following the above link and going through the required registration/request process.
Once you have this file, you drop it in:

$OETREE/openembedded/recipes/powervr-drivers/libgles-omap3

and then run:

bitbake libgles-omap3-3.00.00.09

which generates the following packages:

libgles-omap3_3.00.00.09-r1.1_armv7a.ipk
libgles-omap3-dbg_3.00.00.09-r1.1_armv7a.ipk
libgles-omap3-demos_3.00.00.09-r1.1_armv7a.ipk
libgles-omap3-dev_3.00.00.09-r1.1_armv7a.ipk
libgles-omap3-tests_3.00.00.09-r1.1_armv7a.ipk

Deploy the x11-image to an sd-card, and copy these packages to the sd-card
for deployment on the target. If your beagle board does not have internet
access you will probably also require:

*  devmem2
*  libx11-6 (Only if you insisted on using a console build!)

as opkg will not be able to automatically install the required dependencies
from its repositories and you would hit the following error at deployment:

----------------------------------------------
root@beagleboard:/opt/deploy# opkg install ./libgles-omap3_3.00.00.09-r1.1_armv7 a.ipk
Installing libgles-omap3 (3.00.00.09-r1.1) to root...
libgles-omap3: unsatisfied recommendation for libgles-omap3-tests
Collected errors:
* ERROR: Cannot satisfy the following dependencies for libgles-omap3:
*  devmem2 *  libx11-6 (>= 1.1.5) *
----------------------------------------------

Once you have installed all the above packages, please reboot the board.

Your bootargs in U-Boot should look something like:

console=ttyS0,115200n8=noinitrd ip=dhcp rw root=/dev/mmcblk0p2 omapfb.mode=dvi:1280x720MR-16@60

assuming you want to output via DVI and are running a similar kernel
version (2.6.29-omap1 on my beagle) which accepts the same kernel
arguments indicated in the bootargs variable above.

Please note that we are specifying a 16 bit color depth which is intentional
and discussed in the "color depth considerations" section in the appendix

Please run the powervr demos (under X11) to establish that your drivers are
successfully installed and usable.

Configuring Qt

In order to build Qt now, all that is required for each target is an
appropriate mkspec:

For Qt/X11

You would fork your mkspec off the linux-g++ mkspec, the resulting mkspec's
qmake.conf would resemble:

==================================================================
.............
include(../common/linux.conf)

# modifications to g++.conf
# These release optimization flags are TI supplied
# and a little more aggressive than Qt standard (gentoo types rejoice!)
QMAKE_CFLAGS_RELEASE     = -O3 -march=armv7-a -mtune=cortex-a8 -mfpu=neon -mfloat-abi=softfp
QMAKE_CXXFLAGS_RELEASE     = $$QMAKE_CFLAGS_RELEASE

QMAKE_CC         = $FULLY_QUALIFIED_COMPILER_PREFIX-gcc
QMAKE_CXX         = $FULLY_QUALIFIED_COMPILER_PREFIX-g++
QMAKE_LINK         = $FULLY_QUALIFIED_COMPILER_PREFIX-g++
QMAKE_LINK_SHLIB     = $FULLY_QUALIFIED_COMPILER_PREFIX-g++

# modifications to linux.conf
QMAKE_LIBS_EGL         = -lEGL -lIMGegl -lsrv_um
QMAKE_LIBS_OPENGL_QT     = -lEGL -lGLESv2 -lGLES_CM -lIMGegl -lsrv_um
QMAKE_LIBS_OPENVG     = -lEGL -lGLESv2 -lGLES_CM -lIMGegl -lsrv_um -lOpenVG -lOpenVGU

QMAKE_INCDIR         = $TARGET_STAGING_PATH/usr/include
QMAKE_LIBDIR         = $TARGET_STAGING_PATH/usr/lib

QMAKE_AR         = $FULLY_QUALIFIED_COMPILER_PREFIX-ar cqs
QMAKE_OBJCOPY         = $FULLY_QUALIFIED_COMPILER_PREFIX-objcopy
QMAKE_STRIP         = $FULLY_QUALIFIED_COMPILER_PREFIX-strip

load(qt_config)
==================================================================

and you would configure Qt with:

configure -arch arm -xplatform linux-omap3-g++ -opengl es2 -openvg

all that remains is to adjust /etc/powervr.ini on the target to be:

[default]
WindowSystem=libpvrPVR2D_FLIPWSEGL.so

Now compile an example, eg:

./examples/opengl/hellogl_es2

deploy it and Qt to the target and enjoy.

For Qt/Embedded

Since we don't have the X11 abstraction, we have to interface with the
underlying hardware/interfaces with Qt/Embedded's gfx abstraction layer. We
are going to be making some heavy use of the powervr driver resident under:

$QTSRCTREE/src/plugins/gfxdrivers/powervr

there is a README file in the powervr directory that is definitely
recommend reading, and lends some serious insight into our powervr driver
and Qt/Embedded in general. The same driver is used for MBX/SGX targets and
hence sees a fair amount of usage on a variety of target devices.

You would fork your mkspec off the qws/linux-arm-g++ mkspec, the resulting mkspec's
qmake.conf would resemble:

==================================================================
................
include(../../common/qws.conf)

# modifications to g++.conf
QMAKE_CFLAGS_RELEASE     = -O3 -march=armv7-a -mtune=cortex-a8 -mfpu=neon -mfloat-abi=softfp
QMAKE_CXXFLAGS_RELEASE     = $$QMAKE_CFLAGS_RELEASE

QMAKE_CC         = $FULLY_QUALIFIED_COMPILER_PREFIX-gcc
QMAKE_CXX         = $FULLY_QUALIFIED_COMPILER_PREFIX-g++
QMAKE_LINK         = $FULLY_QUALIFIED_COMPILER_PREFIX-g++
QMAKE_LINK_SHLIB     = $FULLY_QUALIFIED_COMPILER_PREFIX-g++

# modifications to linux.conf
QMAKE_INCDIR         = $TARGET_STAGING_PATH/usr/include
QMAKE_LIBDIR         = $TARGET_STAGING_PATH/usr/lib

QMAKE_LIBS_EGL         = -lEGL -lIMGegl -lsrv_um
QMAKE_LIBS_OPENGL_QT     = -lEGL -lGLESv2 -lGLES_CM -lIMGegl -lsrv_um
QMAKE_LIBS_OPENVG     = -lEGL -lGLESv2 -lGLES_CM -lIMGegl -lsrv_um -lOpenVG -lOpenVGU

QMAKE_AR         = $FULLY_QUALIFIED_COMPILER_PREFIX-ar cqs
QMAKE_OBJCOPY         = $FULLY_QUALIFIED_COMPILER_PREFIX-objcopy
QMAKE_STRIP         = $FULLY_QUALIFIED_COMPILER_PREFIX-strip

#These defines are documented in the powervr README, please read it
DEFINES += QT_QWS_CLIENTBLIT QT_NO_QWS_CURSOR

load(qt_config)
==================================================================

and you would configure Qt with:

/opt/dev/source/qt-beagle-4.6/configure -embedded arm -little-endian -xplatform qws/linux-omap3-g++ -opengl es2 -openvg -plugin-gfx-powervr

all that remains is to adjust /etc/powervr.ini on the target to be:

[default]
WindowSystem=libpvrQWSWSEGL.so

Now compile an example, eg:

./examples/opengl/hellogl_es2

deploy it and Qt to your board, and after shutting down X, run the example with
the following arguments:

./hellogl_es2 -qws -display powervr

-qws - starts the application as the QWS server with exclusive access to the
system hardware which manages all subsequent Qt "client" applications

-display powervr - indicates that Qt should use the powervr driver we
compiled earlier

Summary

I hope that this posting encourages people to go forward and experiment
with a fully accelerated Qt 4.6 on the beagle board. Offloading the
painting work onto the GPU drastically reduces the load on the CPU and
broadens the range of applications which can feasibly be run on this
broadly available (cheap!) embedded hardware. The Beagle board has
really nice hardware, and it would be infinitely useful for us to have external
people using our powervr driver and getting it as broadly used/refined as
possible.

Appendix

Additional Benefits to OpenGL ES acceleration

If you take any Qt Graphics View based example and set a QGLWidget as its
viewport, a large amount of work will be offloaded on the GPU leaving your
CPU free to frolic. To put this in perspective, a modified version of:

./examples/animation/animatedtiles

which continually transitions runs smoothly at 720p on the beagle board
when using software, but consumes 100% CPU time according to top (99.3% to
be fair). It is therefore CPU bound and you are not going to be doing
anything else in the background.

When backed by a QGLWidget, the CPU usage drops to 20% on the exact same
example in the exact same conditions (720p, at 16bit color depth). The
frame rate suffers slightly, but at least this is mandated by the GPU

Minor clipping issue evident in hellogl_es2

The bubbles are evidently clipped on the right hand side, I will hopefully
beat you to reporting this at: http://bugreports.qt.nokia.com/secure/Dashboard.jspa

I have not seen any other artifacts, please file any additional bugs you
may encounter at the above URL.

Are these instructions applicable to OMAP3 targets in general

Yes. There is no theoretical reason these instructions would not suffice
for any OMAP3 based target, although I have not personally verified them
outside of Beagle board usage. Caveat emptor.

No Scratchbox2 usage when cross compiling

The more astute of your would recognize that I bypassed Scratchbox2 when
configuring Qt/X11 this time around. I payed dearly for it, and this X11
build has no fontconfig, dbus or glib support even though the Ångström
subsystem I am building against has support for all of them. If you want a
full fledged X11 build with decent font support and OpenGL ES support,
please either:

1) Invest your time in physically adjusting your MKSPEC (and/or wrestling
pkg-config) to get all desired dependencies detected and built against

-Or-

2) Take the easy road, refer to my previous blog posting "Cross compiling
Qt/X11" and merge the above mkspec changes into the:

./mkspecs/unsupported/linux-scratchbox2-g++

mkspec in your Qt 4.6 source tree.

The same goes for Qt/Embedded which is more self sufficient, but which will
be built without dbus, glib, etc and additional external dependency support
without additional mkspec/environment modification or the use of Scratchbox2
to abstract this away.

Color depth considerations

1) The powervr implementation we are relying on does not support
PVRSRV_PIXEL_FORMAT_RGB888 (24bit color depths), it does however support
PVRSRV_PIXEL_FORMAT_RGB565 and PVRSRV_PIXEL_FORMAT_ARGB8888

2) Ångström is busybox based, and the fbset command you will need to set 32
bit color depths on the console will not work with the default fbset
busybox symlink. You will therefore have to install and use fbset(.real)
in order to get 32bit color depths, which is a simple opkg install away for
the connected Beagle board and a bitbake away for the stranded.

Please note the color depth specified in the boot arguments

console=ttyS0,115200n8=noinitrd ip=dhcp rw root=/dev/mmcblk0p2 omapfb.mode=dvi:1280x720MR-16@60

if you want 32 bit color depth, use:

console=ttyS0,115200n8=noinitrd ip=dhcp rw root=/dev/mmcblk0p2 omapfb.mode=dvi:1280x720MR-24@60

followed by:

/usr/sbin/fbset.real -depth 32 -rgba 8/16,8/8,8/0,8/24

after your Linux kernel drops you in userspace with a kiss on the cheek. A
brave man once tried leaving the color depth at 16 in his boot args, and
jumping all the way to 32bit with fbset so he could change between the more
performant 16 bit color space and the hardware compositing ARGB offering.
Running the dedicated fbset command halved his vertical resolution
regardless of any other parameters he tried to pass fbset and he eventually
ran off to fight another day.

There is a clear performance hit of 7 fps when running hellogl_es2 in
32bit rather than 16bit, taking you down to 20 fps. This hit is even more
pronounced when setting a QGLWidget on the viewport of a QGraphicsView. I
am not sure who is responsible for this, and will be personally
investigating it in the future. Any conjecture/feedback/research performed
by the reader would be greatly appreciated.

*Edited: Introduce rudimentary formatting to make the blog look less Vim forged