Generally, I reset a timer every time a new byte comes in. When the=20
timer expires, I consider that to be the end of the packet.

That works pretty well for me but in my case, the bytes are fairly=20
close to each other, and the time between packets is much longer than=20
one byte time.  This doesn't work if the packets are really close together.

dwayne


At 10:50 AM 2/2/2014, Andre Abelian wrote:
>Hi All,
>
>I am having hard time to determine the length of  uart RX data. the=20
>data length is unknown it is between (100-125 byte) and it is less=20
>then 128 bytes.
>in my routine RX ISR clears the RX flag and saves the byte came in=20
>and increases the counter. data_available is not used for now
>
>void __attribute__((interrupt, no_auto_psv)) _U2RXInterrupt(void) {
>
>     uint8_t data_size_U2;
>
>         IFS1bits.U2RXIF =3D 0;
>         if (U2STAbits.URXDA =3D=3D 1)
>         {
>             U2_RX[new_counter] =3D U2RXREG;      // save incoming byte
>
>             counter++;     // increment
>             data_available =3D 1;
>             GLED_ON;
>         }
>
>}
>
>
>the counter contains total number of bytes but the question is how=20
>to check when no more data is coming in? to use the counter.
>I was testing with IDEL flag     U2STAbits.RIDLE I can see when uart=20
>RX is active  the flag is set to 0. now the problem is
>even on first receive byte the flag will indicate as busy. so just=20
>using when it is busy is not going to work.
>in my case I do not mind to deal with fixed 128 byte every time I=20
>already know the data is some where between
>100-125 bytes. the only issue is when there is no data coming in the=20
>interrupt will not occur and counting extra is not going to work.
>  the counter in ISR knows exact  length of bytes came in but I do=20
> not know when to check the counter since I do not know the length of data=
..
>i am not sure if I explain clearly. the counter and U2_RX are global=20
>variables.
>
>any idea or suggestion will appreciate.
>
>thanks
>
>Andre


--=20
Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
www.trinity-electronics.com
Custom Electronics Design and Manufacturing

--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.