Chapter 8: Bringing Up the Board for the First Time

Having designed, constructed, cleaned, and inspected the printed circuit board, it is now time to apply power – in other words, perform the infamous smoke test. This chapter will lead you through the process of carefully providing first-time power to the board and checking basic circuit-level functionality. If you discover any problems, this chapter contains suggested approaches for fixing them. Once the board has passed these tests, we will continue to work on the FPGA logic, and will test the digital interface to the oscilloscope board.

After completing this chapter, you will have learned how to prepare the circuit for initial power application and how to test circuit components for proper operation. You will also understand how to identify and fix problems with the assembled circuit, and will have also checked out the digital interface to the circuit board.

We will cover the following topics in this chapter: ...

Technical requirements

The files for this chapter are available at https://github.com/PacktPublishing/Architecting-High-Performance-Embedded-Systems.

To perform the checkout procedures on the digital oscilloscope circuit board, you will need a multimeter capable of measuring DC voltages. To examine the clock and data signals, you will need an oscilloscope with a bandwidth of at least 40 MHz.

Preparing for power-up

Chapter 7, Building High-Performance Digital Circuits, took us through the steps of constructing, cleaning, inspecting, and performing basic electrical checks on the digital oscilloscope circuit board. We are now ready to apply power to the board and perform testing to determine whether it is operating correctly.

Before applying power to the board, it is important to keep in mind that you need to exercise care when handling it and while it is operating. The integrated circuits on the board remain susceptible to damage from electrostatic discharge (ESD), and it is easy to cause damage when you're probing parts of the circuit with metallic multimeter or oscilloscope probes. It is best to perform this work in an ESD-controlled environment, such as on the mat you use for soldering, and with a wrist strap in place.

If you must work with the board in a non-ESD-controlled environment, you should carefully handle the board by the edges and avoid touching the...

Checking our circuit's basic functionality

With power flowing to the board, we can start checking the DC behavior of the circuitry. This testing can be performed with a standard multimeter set to cover the range -4.0 to +3.3 V, which is typically the 20 V range.

Attach a clip lead to the multimeter's ground connection. Connect the ground clip to the GND test point on the digital oscilloscope circuit board.

Attach a probe-type lead to the multimeter's DC voltage input. This lead should come to a point, which will allow you to accurately contact small target locations on the PCB.

The following photo shows clip- and probe-type multimeter leads:

Figure 8.1 – Clip- and probe-type multimeter leads

We will be using the KiCad circuit schematic and PCB layout diagram to identify specific circuit points for testing with the multimeter. The schematic allows us to easily locate the features of the circuit we are interested in checking. The...

Adapting the circuit in case of problems

In Chapter 7, Building High-Performance Digital Circuits, we discussed various techniques for repairing problems resulting from improper assembly of the circuit board. The base assumption behind those procedures was that the circuit design was correct, and that any issues that arose were related to the assembly process.

You may reach a point where you identify one or more problems with the design of the circuit itself during testing. Once a design problem has been identified, it might be straightforward to revisit the circuit schematic and make the necessary corrections. The immediate problem, though, is that the PCB you are working with cannot be fixed as easily. Ordering a revised board will cost money and take time. It may be helpful to explore the possibility of modifying the PCB in order to implement immediate design changes.

Depending on the specific problem, it may be possible to make some modifications to the circuit board that...

Summary

This chapter led you through the process of carefully providing first-time power to the board and checking basic circuit-level functionality. After passing those tests, we added some FPGA code to generate the output signals that drive the oscilloscope board. We also discussed some ways we can modify and adapt the circuit if it turns out to not be functioning as intended.

Having completed this chapter, you now know how to prepare the circuit for initial power application and how to test circuit components and subsystems for proper operation. You have learned how to drive FPGA output signals and understand how to modify and adapt the circuit in case of design problems.

The next chapter will expand on the digital oscilloscope execution algorithm, including the remaining FPGA implementation, the firmware running on the MicroBlaze processor, and the software application running on the host computer.