Even a tiny test pad that can connect to it for debugging is enough. There are also analog techniques for testing firmware in the system.
For mixed-signal systems, they involve meeting the analog designer halfway and putting out signals for an oscilloscope. This is a very powerful technique. Again, it can only be used if a pin is available. Another tool can meet the analog designer more than halfway, getting digital firmware to output an analog representation of an internal value.
This is possible because often there is a spare pulse-width modulator PWM or a digital-to-analog converter DAC pin available. To use this technique, the firmware puts an internal signal out on the pin. With a simple low-pass filter, this signal can be turned into a continuous waveform that can be observed on the scope at the same time as the analog signals for the rest of the system. The first step was to verify that the signals were getting through the ADCs cleanly.
The next step was to watch the signal go through the internal filters and come out on the other side. If you have a digital proportional, integral, derivative PID , you can look at the output of each term.
You can look at the error input to the PID. This gives the exact value at this point. These techniques are indispensable in the design of mixed-signal systems and as analog and firmware engineers spend more time together. The general awareness of such techniques will lead to faster and more efficient designs.
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Sometimes it may be worthwhile to complete an initial prototyping with a bigger version of the chip, one with more pins for more instrumentation, and maybe a bigger version of the board with test points and built-in filters for the extra PWM pins. In any case, try to squeeze in little test pads for the serial port, a digital line, and a PWM, or more if you can.
Everyone will be glad you did! Firmware engineering works the other way as well. Even though the analog signals are on the outside, visible to anyone watching, the program only knows about them if they are hooked up to a pin. Otherwise the program will keep trying to run the power supply. If there is a host interface, it may not report the power supply state correctly. Another difference is simultaneity versus sequence. In an analog system, things tend to run simultaneously.
In a firmware system, instructions are executed sequentially. Sometimes, the implications are not always clear to analog designers. First, only a few things can be done that frequently. So for a kHz switching rate, only instruction cycles are available. Lots of them take two or three or four cycles. Then the whole program execution has to fit into those cycles. If you dedicate cycles to the end of the period, you now have only a 2-MHz processor for everything else, which may not be enough.
Second, it is difficult for firmware to do things at an exact time. There is an end of the switching period interrupt, but there is always a four-instruction-cycle overhead for entering the interrupt. So if the interrupt occurs at the end of an instruction, it takes about ns four cycles to start. If the interrupt occurs at the start of that cycle instruction, it takes about a microsecond.
The timing of the interrupt, then, may not be very precise. The ARM-based system has a slower processor with sophisticated peripherals specifically designed to do things at the end of the cycle, relieving the firmware of this duty. A DSP-based system may have a faster processor that can respond quicker, but the same basic issues are still present.
Optimizing the allocation of processor bandwidth is a complex and arcane art practiced mainly by firmware engineers. But if a power-supply control takes too long to sort out a fault, equipment could be damaged. To be sufficiently robust enough against parameter variations, robustness of parameters is introduced in these specifications. The efficacy of the technique is demonstrated for the benchmark voltage controlled and tunnel diode oscillators. Library Services. Unpublished Doctoral thesis, City University London Abstract This thesis presents novel formal verification techniques to verify the important property of inevitability of states in analog and mixed signal AMS circuits.
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Designing Analog Mixed-signal Circuits - Mentor Graphics
Mixed signal integrated circuits. Stratigopoulos, H. Institute of Electrical and Electronics Engineers Inc.. Institute of Electrical and Electronics Engineers Inc. Access to Document
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