nRF51-DK printf() causes hang when PC serial port not active / not opened.

[nuket]

Already reported this once in the mbed OS codebase, here's another concrete example of this happening.

The problem is that, with the nRF51-DK hooked up to my computer, if I don't connect to and open the serial port exposed as /dev/ttyACM0, whatever software is running on the DK board will just hang. It seems like the Nordic serial port code locks up because it always expects some hardware flow control of some sort, so that if I don't have minicom running, it doesn't work. Also, if I run minicom then exit from it, the DK board will keep running for a while, then eventually hangs.

The Nordic serial port code simply does not work properly. Where, in the HAL (pun intended), do I fix that?

Here's a video of this happening.

The video shows the code example from my fork here, which is running:

• At the start, the board is hung, because I don't have minicom open.
• I open minicom, the board starts printing "Alive." again.
• I close minicom, the board eventually hangs again.

[nuket]

Here's the .mbed configuration I'm using:

$ cat .mbed
TARGET=NRF51_DK
TOOLCHAIN=GCC_ARM
GCC_ARM_PATH=/home/max/devtools/gcc-arm-none-eabi-5_4-2016q2/bin
ROOT=.

I've tried with GCC 4.9 and 5.4, both exhibit identical behavior.

[nuket]

Related issue, possibly: ARMmbed/mbed-os#2474

[sg-]

Can you confirm is #2535 resolved this issue?

[nuket]

I will take a look.

[nuket]

Confirmed ARMmbed/mbed-os#2535 resolved the issue after adding to mbed_app.json:

"NRF51_DK": {
    "target.uart_hwfc": 0
}