How do I configure newlib printf?

RE: How do I configure newlib printf?

Marcel Mulder — Thu, 15 Jan 2015 08:11:51 GMT

I also use (GCC but with QT Creator. I also used the GCC Makefile supplied by Nordic. They both work with app_trace(). Could you share the linker options you use?

RE: How do I configure newlib printf?

Peter — Wed, 14 Jan 2015 23:36:08 GMT

I voted up all the other answers since they provided excellent info.

RE: How do I configure newlib printf?

Peter — Wed, 14 Jan 2015 23:34:12 GMT

Newlib printf doesn't need to be configured (other than making sure the items you want to use are defined as pabigot mentioned.

However, newlib does put some items in the .data section, namely impure_data. In my case, I had totally messed up my sections. .data was not getting initialized, and impure_data was pointing off where it shouldn't. Because of this, printf would crash when it tried to dereference impure_data.

So if your .data section is not being initialized, printf will fail.

RE: How do I configure newlib printf?

cocoa — Wed, 14 Jan 2015 19:50:53 GMT

Right, you will use JLinkRTTClient and not JLinkSWOViewer.

RE: How do I configure newlib printf?

pabigot — Wed, 14 Jan 2015 19:16:28 GMT

Yes. I was unaware of the retarget.c feature since I don't use anything but the CMSIS headers from the Nordic SDK.

I've also run into trouble where two things (e.g. retarget.o and -lnosys) define the same symbol, especially if they both come from libraries, as the order the libraries are read by the linker becomes important. In BSPACM I use weak symbols for the stubs to avoid some of these problems.

RE: How do I configure newlib printf?

Peter — Wed, 14 Jan 2015 19:09:27 GMT

But doesn't the nosys library just provide stubs for functions that are undefined? i.e., since retarget.c defines _read and _write, those versions will be used instead of the stubs in nosys. I can test this by commenting out _write in retarget.c--when I print the symbols with nm, _write comes from somewhere else (nosys I assume) and _read comes from retarget.c. Can't I let nosys define stubs for functions I don't care about like _exit?

RE: How do I configure newlib printf?

Peter — Wed, 14 Jan 2015 18:53:27 GMT

So just to confirm: The SWV console doesn't require SWO, right? Because SWO isn't supported on the NRF51-DK.

RE: How do I configure newlib printf?

Peter — Wed, 14 Jan 2015 18:41:52 GMT

I did add it. _write and _read appear in my .elf (and the debug symbols show that they come from retarget.c. My app crashes before those ever get called though.

RE: How do I configure newlib printf?

cocoa — Wed, 14 Jan 2015 13:34:18 GMT

If you're using Jlink , printf is available trough Eclipse ARM plugin in Semihosting and SWV console.

Automatically added by plugin to linker : --specs=rdimon.specs -Wl,--start-group -lgcc -lc -lc -lm -lrdimon -Wl,--end-group

If you need a realtime printf, use Segger RTT library, is free.

-c

RE: How do I configure newlib printf?

Marcel Mulder — Wed, 14 Jan 2015 10:10:11 GMT

Did you add nrf51-sdk/components/libraries/uart/retarget.c to your project?

RE: How do I configure newlib printf?

pabigot — Wed, 14 Jan 2015 03:14:42 GMT

BSPACM provides some information about its newlib interface. I use printf and related stdio functions on nRF51 hardware with this solution.

In short you need to provide implementations of the system functions newlib expects. (Be aware that the nRF51 SDK, like many other ARM Cortex-M vendor libraries, hides a reference to -lnosys in a GROUP directive in the linker script. You'll need to get rid of that.)