Logic Analyzer on Chips

The Internet is full of low-speed logic analyzer designs that use a CPU. There are also quite a few FPGA-based designs. Both have advantages and disadvantages. FPGAs are fast and can handle lots of data at once. But CPUs often have more memory and it is simpler to perform I/O back to, say, a host computer. [Mohammad] sidestepped the choice. He built a logic analyzer that resides partly on an FPGA and partly on an ARM processor.

In fact, his rationale was to replace built-in FPGA logic analyzers like Chipscope and SignalTap. These are made to coexist with your FPGA design, but [Mohammad] found they had limitations. They also eat up die space you might want for your own design, so by necessity, they probably don’t have much memory.

The system can capture and display 32-bit signals on a 640×480 VGA monitor in real-time. The system also has a USB mouse interface which is used to zoom and scroll the display. You can see a video of the thing in operation, below.

You can always opt for simulation, but sometimes you really need to run your design on actual silicon. There are subtle failures or even interactions with other hardware that are difficult to model in simulation.

There are several interesting design features to the analyzer, including the use of the Xillybus core to simplify interfacing from FPGA logic to the ARM AXI bus. This simplifies the communications with the ARM processor greatly.

We’ve looked at inexpensive FPGA-based logic analyzers before. You could use these integrated if you have any room left on your device. If you don’t feel the need for speed, you could opt for a CPU-based design.

If you couldn’t tell, this is one of the projects from [Bruce Land’s] students. Thanks [Bruce] for the tip and for what you do creating the next generation of hardware hackers.

Filed under: ARM, FPGA