AHB on-chip Bus Tracer (BT)
The BT supports four tracing modes which record the bus signals
at various levels of abstraction (cycle mode, encoded cycle mode,
transaction mode, and encoded transaction mode) [2]. Fig. 1 shows
the block diagram of the BT. The first stage is the monitor stage,
which monitors the bus activities and triggers the trace capturing
under the selected trace mode. In addition, an FSM is used to identify
the bus transaction. The second stage is the data reducing stage in
which the bus signals are abstracted, encoded and compressed. The
bus address is compressed with a differential scheme, and the bus
control signals are encoded by an encoder based on a table lookup
mechanism. Then these signals are compressed with a dictionary
approach followed by a slicing method. Finally, the trace is packed
and output to the trace memory or the trace port. With these sophisticated mechanism, the BT is able to greatly reduce the trace size,
ranging from 78% to 98% depending on the mode used. The output
trace can be decoded and visualized by a VCD (value change dump)