As FFado has made it into the Ubuntu Jaunty archives, it is being built on more archs than just i386 and amd64. Relevant section from the build log:
g++ -o src/bebob/bebob_avdevice.os -c -DDEBUG -Wall -g -DDBUS_HAS_THREADS_INIT_DEFAULT \
-DENABLE_BEBOB -DENABLE_FIREWORKS -DENABLE_MOTU -DENABLE_GENERICAVC -fPIC -I. -Isrc \
-I/usr/include/libxml++-2.6 -I/usr/lib/libxml++-2.6/include -I/usr/include/libxml2 \
-I/usr/include/glibmm-2.4 -I/usr/lib/glibmm-2.4/include -I/usr/include/sigc++-2.0 \
-I/usr/lib/sigc++-2.0/include -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include \
-Iexternal/libconfig src/bebob/bebob_avdevice.cpp
In file included from src/libutil/Thread.h:56,
from src/libstreaming/StreamProcessorManager.h:32,
from src/devicemanager.h:33,
from src/bebob/bebob_avdevice.cpp:26:
src/libutil/Atomic.h: In function 'long int INC_ATOMIC(volatile int32_t*)':
src/libutil/Atomic.h:170: error: 'CAS' was not declared in this scope
src/libutil/Atomic.h: In function 'long int DEC_ATOMIC(volatile int32_t*)':
src/libutil/Atomic.h:179: error: 'CAS' was not declared in this scope
src/libutil/Atomic.h: In function 'long int ADD_ATOMIC(volatile int32_t*, int32_t)':
src/libutil/Atomic.h:188: error: 'CAS' was not declared in this scope
src/libutil/Atomic.h: In function 'long int SUBSTRACT_ATOMIC(volatile int32_t*, int32_t)':
src/libutil/Atomic.h:197: error: 'CAS' was not declared in this scope
src/libutil/Atomic.h: In function 'long int ZERO_ATOMIC(volatile int32_t*)':
src/libutil/Atomic.h:206: error: 'CAS' was not declared in this scope
scons: *** [src/bebob/bebob_avdevice.os] Error 1
scons: building terminated because of errors.
make: *** [debian/stamp-scons-build] Error 2
Full build log: http://launchpadlibrarian.net/22779537/buildlog_ubuntu-jaunty-sparc.libffado_2.0~rc1-0ubuntu1_FAILEDTOBUILD.txt.gz