  We present a timing analysis of the 2009 outburst of the accreting
millisecond X-ray pulsar Swift J1756.9-2508, and a re-analysis of the 2007
outburst. The source shows a short recurrence time of only ~2 years between
outbursts. Thanks to the approximately 2 year long baseline of data, we can
constrain the magnetic field of the neutron star to be 0.4x10^8 G < B < 9x10^8
G, which is within the range of typical accreting millisecond pulsars. The 2009
timing analysis allows us to put constraints on the accretion torque: the spin
frequency derivative within the outburst has an upper limit of $|\dot{\nu}| <
3x10^-13 Hz/s at the 95% confidence level. A study of pulse profiles and their
evolution during the outburst is analyzed, suggesting a systematic change of
shape that depends on the outburst phase.
