@mfalkvidd I'm using an AVR board for my serial gateway. I modified hwDebugPrint in MyHwAVR.cpp with an extra #ifndef to look for MY_DEBUGDEVICE or copy MY_SERIALDEVICE to it. Then all occurrences of MY_SERIALDEVICE were changed to MY_DEBUGDEVICE.

I added this to my sketch:

#define MY_DEBUGDEVICE Serial  // Redirect debug to Serial

The result was what I wanted. Controller <-> Gateway configuration went over Serial1 (/dev/ttyS0 on my RPi) and debugging output went to Serial (/dev/ttyACM0 on my RPi). This allows me to easily debug without having to take any special steps with my controller.

void hwDebugPrint(const char *fmt, ... )
{
#ifndef MY_DEBUGDEVICE
#define MY_DEBUGDEVICE MY_SERIALDEVICE
#endif
#ifndef MY_DISABLED_SERIAL
	char fmtBuffer[MY_SERIAL_OUTPUT_SIZE];
#ifdef MY_GATEWAY_SERIAL
	// prepend debug message to be handled correctly by controller (C_INTERNAL, I_LOG_MESSAGE)
	snprintf_P(fmtBuffer, sizeof(fmtBuffer), PSTR("0;255;%" PRIu8 ";0;%" PRIu8 ";%" PRIu32 " "),
	           C_INTERNAL, I_LOG_MESSAGE, hwMillis());
	MY_DEBUGDEVICE.print(fmtBuffer);
#else
	// prepend timestamp
	MY_DEBUGDEVICE.print(hwMillis());
	MY_DEBUGDEVICE.print(F(" "));
#endif
	va_list args;
	va_start (args, fmt );
	vsnprintf_P(fmtBuffer, sizeof(fmtBuffer), fmt, args);
#ifdef MY_GATEWAY_SERIAL
	// Truncate message if this is gateway node
	fmtBuffer[sizeof(fmtBuffer) - 2] = '\n';
	fmtBuffer[sizeof(fmtBuffer) - 1] = '\0';
#endif
	va_end (args);
	MY_DEBUGDEVICE.print(fmtBuffer);
	MY_DEBUGDEVICE.flush();
#else
	(void)fmt;
#endif
}

@mfalkvidd I'm quite willing to open a pull request. This will be my first time. Do you want me to create an issue as well? Also what would this be called? Perhaps something like "Alternate Port Debugging"? It's hard to think of something that's 'googlable'.