Retarget printf on STM32G070RBxx Cortex M0+

[AVerm.4]

Hi,

I'm trying retarget printf. My uart_write function is working correctly and i'm able to see character on Teraterm.

But when i try to use printf it is not working. i even tried semihosting to execute printf but it fails. i'm attaching the screenshots -

Disassembly of the code stucks at "bkpt 0x00ab" -

any solution for this problem? 

[Andrew Neil · Accepted solution]

Just noticed that you are doing this in C++

The linked articles are both just C, and I have just used C.

Could you try this in a plain C project to see if that makes a difference?

EDIT:

See: https://community.st.com/t5/stm32cubeide-mcus/stm32cubeide-c-redirected-printf-no-longer-works-how-to-use-cout/m-p/285002/highlight/true#M14943 

[AVerm.4]

Tried with the C project as well it's not working.

It printed few lines then threw some garbage. I retried debugging but now nothing displayed on terminal.

Do I need to increase baud rate from 9600 to 115200? Because it's taking time to print.

 

 

[Andrew Neil]

---

@AVerm.4 wrote:

it's taking time to print.

---

What do you mean by that?

Remember that printf is line-buffered - it won't (usually) send its output until it gets a newline...

stderr isn't buffered:

https://community.st.com/t5/stm32cubeide-mcus/can-t-get-printf-to-work-on-cubeide/m-p/701740/highlight/true#M29337

[Andrew Neil]

---

@AVerm.4 wrote:

Sorry missed to mention i have disabled semihosting.

---

and that's stopped the BKPT problem?

[AVerm.4]

@Andrew Neil 

Because I stopped semihosting in this new C project it is not getting stuck at BKPT.

Note - It's not getting stuck at BKPT even in C++ project if not using semihosting.

[AVerm.4]

@Andrew Neil 

"Time to print" i mean to say, it's stuck in buffer before displaying in the terminal. Like it takes couple of minutes to display in terminal when I'm using printf. 

[Andrew Neil]

As noted, that's expected behaviour for stdout (used implicitly by printf)

From the other threads, you should be able to disable the buffering with:

setbuf( stdout, NULL );

https://en.cppreference.com/w/c/io/setbuf 

Or use stderr

Or just send a newline.

[AVerm.4]

For C++ we need to add the extern "C"..

Thanks for the suggestions.!

[Andrew Neil]

@ST AME Support NF @STTwo-32 can the knowledge base article please be updated to note this?

I think the article also needs to explain about the line-buffering - as that is a frequent cause of problems!

[KDJEM.1]

Hello @Andrew Neil ,

Thank you for this proposal. I reported this request internally. 

Your feedback and request are welcome.

Thank you.

Kaouthar