The second Click Shield article in the series is here, and this time we’ll take a look at the synchronization of multiple Red Pitayas using Red Pitaya Click Shields. When talking about synchronization, we’re referring to clock and trigger synchronization of multiple devices, which means all the devices in the chain share the same clock signal ensuring all the important processes like data acquisition and generation happen at exactly the same moment.
Here's a simple, everyday example of synchronization: Imagine arriving at the bus stop at 06:58 and checking the bus schedule to see when the next bus arrives. The schedule says the first bus arrives at 07:00 and then every 20 minutes. If the bus is synchronized with the schedule, it'll arrive exactly on time at 07:00, but if not then it might arrive five minutes late, or even worse, five minutes early, which means we’ve already missed it and might be late for work. Now let’s imagine three desynchronized buses on the same line, each still arriving in exact intervals of 20 minutes, but one is always three minutes early, the second is always seven minutes late, and the final one is always on time. However, if the buses are fully synchronized with the schedule then they always arrive exactly on time – at 07:00, 07:20, and 07:40. But enough about buses and the worry of being late for work, and let's get back to the Click Shields.
To simplify the situation we’ll assume we want to synchronize three Red Pitaya boards, although the following instructions can easily be upscaled for complex projects.
OK, now that we have everything ready, let’s dive in.
One of the main abilities of a Red Pitaya Click Shield is the synchronization of multiple Red Pitaya units. As U.FL cables are used for clock and trigger synchronization, other external clock devices can also be included in the chain. The connection provides minimal clock signal delay between multiple Red Pitaya units, as there is only a single ZL40213 LVDS clock fanout buffer between two units.
In this article, we present two possible synchronization configurations. The first uses the onboard Click Shield oscillator as the clock source and the primary Red Pitaya unit’s trigger signal as the external trigger source. The second version uses both an external clock source and an external trigger source.
We establish the following connections with U.FL cables between the primary board and secondary board, place the corresponding jumpers, and change the switch positions on each Click Shield as explained below.
Primary board:
Secondary boards:
We establish the following connections with U.FL cables between the primary board and secondary board and place the corresponding jumpers on each Click Shield into the shown positions. Here all boards can be treated as secondary, as no unit is the source of either clock or trigger signals.
Primary and Secondary boards:
The instructions set out above can easily be mixed and matched if we want some other combination of clock and trigger signals. For example, perhaps we have an external clock but want the primary device to transmit its trigger signal to all the other devices.
The final step is to configure the software. Here is a quick illustration of how to arrange the external trigger source for the primary board for the oscillator example given above:
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