read </dev/ttyO4 opens the file and after the command is done it is closed.
The UART throws away characters received while the tty is closed.
What you can do is
for … do
read
done </dev/ttyO4
Am 18.05.2015 um 15:18 schrieb [email protected]:
> I have a problem with ttyO4. It looks like something is emptying the uarts
> buffer.
>
> When is run two bash scripts at the same time I can send characters and
> receive characters at the same time. The two files running parallel look like
> this (simplified):
>
> 1:
> for ((x=0;x<100;x++)); do
> echo -en '\xAA' > /dev/ttyO4
> done
>
> 2:
> for ((x=0;x<100;x++)); do
> read -n 1 -t 1 < /dev/ttyO4
> done
>
> Number 1 is sending and I receive the 0xAA at number 2.
>
> Now I try to combine these two files:
>
> for ((x=0;x<100;x++)); do
> echo -en '\xAA' > /dev/ttyO4
> read -n 1 -t 1 < /dev/ttyO4
> done
>
> This does not work. So I write one byte and I am to late to receive this
> byte. When I use the bash script reading parallel it works again.
>
> The 0xAA received at the RX, where does it go? Why isn't it in the
> Beaglebones (hardware) buffer? Is there some linux process reading these
> bytes before my own read (from the bash file) is ready to read?
>
> --
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