nRF5x UART Hang

[AGlass0fMilk]

Description

Hi, I'm recently synced my fork of mbed-os and pulled in the updated nRF5x serial API changes. I also noticed the base class in target.json introduced the following concerning UART HWFC:

mbed-os/targets/targets.json

Lines 15 to 19 in 6361e92

	"config": {
	"console-uart-flow-control": {
	"help": "Console hardware flow control. Options: null, RTS, CTS, RTSCTS.",
	"value": null
	}

I had to change my custom target to remove the hardware flow control override (I dealt with this issue in the past, see issue ARMmbed/mbed-os-example-ble#25 ) since this is not part of the base class anymore.

I'm now seeing a hang when trying to print to a UART/serial. It's hanging at the following busy-wait loop for the TXend event:

mbed-os/targets/TARGET_NORDIC/TARGET_NRF5x/serial_api.c

Lines 1476 to 1478 in 6361e92

	/* Busy-wait until the ENDTX event occurs. */
	while (!nrf_uarte_event_check(nordic_nrf5_uart_register[instance], NRF_UARTE_EVENT_ENDTX));

Is there an equivalent fix for this? My custom target does not even have hw flow control pins broken out so that's not an option.

@marcuschangarm

(Sorry for blowing up the issues tab)

[marcuschangarm]

Hey, can you post your custom_target.json, please?
And is this with a simple Hello World test with printf and nothing else?

[AGlass0fMilk]

The only relevant details from my custom target are:
"inherits": ["NRF52_DK"], "macros_remove": ["BOARD_PCA10040"], "macros_add": ["ENABLE_SWO", "I2C_TIMEOUT_VALUE_US=1000", "BOARD_CUSTOM"],

The other characteristics are for internal configuration.

The program I am running looks like this:

#include "mbed_debug.h"
#include "mbed_wait_api.h"

int main(void)
{
	/** Initialization and thread spinoff goes here */

	while(true)
	{
		/** Application code goes here */
	       debug("hello!");
	       wait_ms(1000);
	}
}

[AGlass0fMilk]

I'm testing the same code on a fresh mbed-os program for the actual NRF52_DK board and I'm getting similar results... no serial output.

[AGlass0fMilk]

Update: I added the following to my mbed_app.json and it fixed the hang:
"target.uart_hwfc": 0

mbed-cli was complaining before that I was trying to override a config parameter that didn't exist (since this was removed from the official mbed targets.json file) but it seems that the code still uses it somewhere? Instead of overriding it, I just added it to the configuration.

[AGlass0fMilk]

For some reason that doesn't work for my custom_target... the stdio_uart still has HWFC enabled... is there a way to disable hardware flow control???

[marcuschangarm]

Ah, I see. You probably want to inherit from MCU_NRF52832 directly and not from NRF52_DK. Flow control is disabled by default but the NRF52_DK enables flow control for itself.

[marcuschangarm]

Depending on your chip revision you should add (some of) these macros as well:

https://github.com/ARMmbed/mbed-os/blob/master/targets/TARGET_NORDIC/TARGET_NRF5x/mbed_lib.json#L87-L107

[AGlass0fMilk]

Thank you for the fix @marcuschangarm... I changed over to inheriting from MCU_NRF52832 and added the errata fix macros.