CM1K Hardware User’s Manual
33
4.3
Timing constraints
When active, the reco_logic becomes the master controller of the neurons, sending them commands to recognize
the vectors received continuously on the digital input bus. To ensure that the recognition sequence is not
interrupted by an external controller, the reco_logic rises the B_BSY signal and the CM1K will discard any
command received while B_BSY is high.
o
B_BSY rises on the negative edge of the system clock as soon as frame valid falls
o
B_BSY falls on the negative edge of the system clock when the CAT_VALID signal.
The only time available to receive and execute an external command is between the fall of the CAT_VAL pulse and
the next rise of F_FV.
If this command is an I2C command, its execution includes the serial decoding/encoding and timing may become
short. Since we can assume that the most relevant registers when the recognition stage is active are the RT_DIST
and RT_CAT, the CM1K I2C controller has been designed to handle them in a special way to waive the timing
constraints mentioned above. They can be read at any time, but this is not true for the other registers such as
CM_LEFT and CM_TOP for example which allow changing the position of the ROI.