When implementing a real-time system, we find a circular buffer critical whether we are using a DSP processor or a general purpose processor (GPP). However, with a GPP we may have to implement the circular buffer in software. As discussed in the previous section, with each new sample, we have to update the pointer which contains the address of the newest sample. With a circular buffer implemented in software, the programmer needs to take care of updating the buffer pointers after each read and write operation. When the pointer reaches the end of the buffer, the program must wrap the pointer back to the beginning of the buffer.
It’s always good to be cognizant of trace lengths when you’re laying out a parallel bus, though at moderate frequencies it is nothing to stress about. The propagation time for a signal traveling through a trace is maybe 150 picoseconds/inch. So if you have two traces with a length mismatch of one inch, one signal will arrive 150 ps after the other signal. If your signals are transitioning at a frequency whose corresponding period is much greater than 150 ps, this one-inch mismatch won’t cause problems. Even at 100 MHz (which is pretty fast for a parallel bus), the period is 10 ns, i.e., ~67 times larger than the time-of-arrival discrepancy for a one-inch mismatch.
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