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by fjfaase 52 days ago
Really strange the the C JSON parser has to use malloc where the RUST version does not. As if it is not possible to write a JSON parser in C that does use malloc. I presume that the syntax of the commands that the device will accept is known, and than there is no reason why you have to build a DOM of the JSON before you can process it. Apparently, the RUST version can do it. I really begin to question the abilities of two teams if the one team failed to implement a JSON parser solution without using memory allocations.
2 comments
kaspar030 52 days ago
Part of the C protocol implementation is generated, and that generator chose the JSON parser. As it worked and there was plenty of memory left on the MCU, it was kept.

We're mentioning this in the paper: "The heap is entirely attributable to Parson's dynamic allocation of JSON tree nodes; as memory usage minimization was not a key goal, we kept Parson (the JSON parser used by the PNPL code generator by default), noting that there are less memory heavy options that do not require a heap at all."

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dundarious 52 days ago
Wasn't memory one of the key indicators looked at?

> The analysis and measurements on hardware indicate no strong reason to prefer C over Rust for microcontroller firmware on the basis of memory footprint or execution speed.

I admit I have not carefully read the paper, and am collating info from comments here, so I may be fully mistaken. The word "strong" also allows for much interpretation, that I'm not a priori critical of, but am skeptical of.

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megous 52 days ago
Yeah, you can comfortably work with JSON in C directly on top of the string buffer containing it. Your representation for any JSON entity will just be const char pointer. It's possible to implement JSON path on top of this, and all kinds of niceties, and it's not slow.

Megatools is an example of such a code https://xff.cz/megatools/ / https://xff.cz/git/megatools/tree/lib/sjson.c

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