Serial1.read() does not decrement Serial1.available()

General
1

It is my understanding that each call to Serial1.read() should read one byte from the Serial1 port, thereby causing a decrement to the byte count provided by a call to Serial1.available.
I have a piece of code that occasionally (approx 2% of the time) fails to decrement the count following a read operation. Am I doing something wrong, or do I misundertand the correct behaviour of these functions?

2

@fguptill, the count won’t decrement if another byte is received at the same time. Byte reception is asynchronous since it is interrupt driven.

3

Thanks peekay123. Makes sense.
So does it follow then that I must turn off the sender while I read bytes in order to prevent subsequent transmissions from contaminating the present one?

4

@fguptill, the serial circular buffer is 32 bytes long so I suggest that you transfer all available data:

while(Serial1.available()) {
  // read all available Serial1 data and possibly buffer or process it
}
5

That is indeed what I am doing, but perhaps I need a tighter loop - i.e. one with fewer operations in it.

BTW, Serial1.available() returns a maximum of 63 in my project. Are you sure about the 32 bytes?

6

@fguptill, I was thinking of the I2C buffer. You are correct, the Serial1 buffer is 64 bytes in size. :blush:

7

Thx peekay123

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