Conclusions and Future Work
future revision of the board must use the CLCC packaged version of the image sensor as this is the only package currently available.
n alternative to the U RT bus is the Blackfin SPORT bus that supports hardware TDM. If the SPORT bus were used then a different USB bridge chip would be required to re- place the FTDI chip. The Blackfin BF547  could be considered for this job as it includes an on board USB peripheral and SPORT bus. Using this approach, the current bandwidth
limit could be increased.
lternatively, the throughput could be increased by sending com-
pressed binary data.
The Soft Hub processes the data from the Black Spot modules.
rudimentary pose es-
timate for single modules under some conditions can be produced. However, the min- imisation algorithm does not converge sufficiently under many conditions. Future work should investigate replacing this algorithm with a bundle adjustment algorithm . This would allow the model of the markers’ 3D locations to be refined while producing pose
and provide software licensed under the GNU General Public Licence (GPL) .
The stationary centroid performance of the Black Spot modules is excellent. The modules were tested while varying three parameters: angle, distance, and marker intensity. The variation in marker intensity had the largest impact on centroid standard deviation but with a shutter period of 300 µs, and maximum intensity values of greater than 80, similar results are produced. With camera-to-beacon distances of between 0.6 m and 3 m there is a slight trend towards greater variation with increasing distance. The centroid standard deviation varies within a module’s FOV with the best performance near the centre of the FOV. Over a period of 2 minutes, the mean standard deviations of a marker near the centre of the FOV were 0.0061 pixels in X and 0.0074 pixels in Y. It is concluded that the centroid calculation exhibits excellent precision.
The implementation of the firmware could be improved. For example, the image capture driver produces erroneous data when the firmware is run from the flash memory. To over- come this, the firmware must be loaded using the debugger. nother issue occurs when the hub uses the flow control line to instruct a Black Spot module to halt transmission. This can cause a buffer overrun in the image sensor driver while the Black Spot is waiting for the hub. The buffer overrun could be avoided by using a Real Time Operating System (RTOS) to allow the image processing routines to run in a different thread from the com-
nother option is to service the driver using a callback from an ISR
that is driven by a timer peripheral. The first method is preferable over the second as it is a more general solution and would make extending the firmware easier.