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Comment by saidinesh5 | Hacker News Reader

This post did raise an interesting question for me though. With Qt being used on microcontrollers these days, It made me wonder about the overhead of signals and slots on single core/single threaded usecases and how that might affect things like power consumption/CPU usage on those devices. I would love to see if someone did a comparison on that.

As for the crazy contrived example they have provided: "Assume I receive 100,000 trades per second from some crypo exchange and if one trade triggers 100 signals than I have 10.000.000 signals per second that is something comparable with the maximum." - They'd have to process the incoming messages on a separate thread (or process) anyway, so they wont drop packets because of the event loop that also processes user input. Then update the GUI once every event loop tick because that's how frequently the UI gets updated anyway.

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The more slowly you can interact with a "crypo exchange" the better, right?

Hahah touche.

> With Qt being used on microcontrollers these days

Is it really though? It's used in embedded systems. I wouldn't call those that can run Qt UIs microcontrollers.

Well they did show it off a lot recently. STM32F7 and STM23H7s. Not sure how many "real companies" use it though.

https://www.qt.io/microcontrollers-st .

As per my old boss, the difference in prices when it comes to these microcontrollers and "less powerful" linux socs is negligible that it wasn't worth trying to target them. Not sure if/how the economics changed over the last 2-3 years either.

"Qt for MCUs" isn't the full Qt library as I understand it, but an entirely separate development

> Qt Quick Ultralite is designed to serve as a rendering engine for the application's graphical user interface (UI). Its implementation is different from the standard Qt, and it does not depend any Qt libraries such as Qt Core or Qt Gui. Hence Qt Quick Ultralite applications need to use standard C++ containers and classes instead of those from Qt. For example, instead of using QObject or QAbstractItemModel, Qt Quick Ultralite provides a simple C++ API to expose objects and models.

> It does not include the following from the Qt world:

> The Qt C++ APIs. The non-graphical modules such as Qt Core and Qt Network. The Add-on modules such as Qt Multimedia, Qt Bluetooth, and others Qt Addon Modules. The non-MCU embedded platforms such as embedded Linux or the mobile platforms.

Interesting. Yeah I wasn't sure what was going on there, but it seems to use a pure C++ QProperty, Qul::Signal and Qul::Object.

https://doc.qt.io/QtForMCUs-2.1/qtul-integratecppqml.html

Which is kind of interesting ...

These days "microcontroller" refers to a part that has self-contained flash and SRAM, and the MMU/Linux-capable SoCs need external mass storage and DRAM to run. So there's a cost adder on the Linux parts. You might also need a denser PCB to handle DRAM signals (although Jay Carlson might be right on this).

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