Serial.flush() and FONA

[peak]

I understand that Serial.flush() is empty for Adafruit FONA. In Print.h:
virtual void flush() { /* Empty implementation for backward compatibility */ }

I need to make sure that all Serial.print() statements are completed before I enter sleep mode for the FONA, otherwise it will be subsequently woken up in Serial.print code (and crashes) instead of in loop().

Is there any code that can accomplish this?

[LIM PHANG MOH]

Are you sure they are empty? flush() could be implemented in Stream class. I could be wrong because I rarely use 32U4.
Try putting some characters into print() and call flush() before sleep. See whether all characters are sent before sleep.

Else it is best to simply put a delay by comparing it to millis(). Just estimate the time by calculating how many bytes you are sending.

[peak]

LIM PHANG MOH,
Again, thanks for your effort. Yes, I did call flush() before sleep and it crashed. Found this code:
u16 flushOutput()
{
u16 count;
while ((count = FifoByteCount()) != 0);
return count; // Returns 0
}
u16 FifoByteCount()
{
return ((((u16)UEBCHX) << 8) | (UEBCLX));
}
It compiles ok but does not wait untill the output buffer is empty.

Regarding delay() : I cannot estimate the number of characters waiting to be output. They come from various libraries with DEBUG_PRINT and the like.
There must surely be a way to interrogate the output queue in the build-in UART in Atmel 32u4.

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