semihosting print too slow

[bernardofca]

I have written my own printf routine which, at the end, calls:

_swiwrite(STDOUT_FILENO, printfString, length);

This works well but it seems that the call is taking quite a lot of time (STM32F0 with ST-LINK/V2). As a result, I lose characters coming from a UART even if I print a very short string.

Is there some data related to the speed of this operation and any way I could speed it up?

This is an unsolicited comment: I am a licensee of VisualGDB . This is definitely the best piece of software I bought… I painfully moved from the ST “classic” peripheral interface to the CUBE. Support from VisualGDB is excellent.

 

[support]

Hi,

This is an unfortunate limitation of the semihosting mechanism. Handling a semihosting call involves stopping the CPU and reading the registers/memory. Due to the USB latencies, this takes tens of milliseconds, so your app will certainly miss some real-time events. The only reasonable workaround we could suggest is to use another UART port to print the diagnostic messages.

That said, it looks like we should be able to create a non-stop semihosting alternative similar to our live variables feature. We will investigate into this and perhaps add it to VisualGDB 5.2 feature list.

[bernardofca]

Thanks for the answer. At least I know that this is an expected behavior. I have a debug UART on the PCB but I am waiting for the mating connector!

[support]

No problem. You can also use the live variables to somewhat monitor what’s happening with our program without stopping it. E.g. define a set of global counters and watch them while your program is running.

[Author]

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