How to read a char from FullDuplexSerial without removing it from buffer?

william chan

Hi,

Actually I am using FullDuplexSerial_rr004 which is quite similar.
Does anyone know how to read a char received without removing it from the receive buffer?

Thanks.

Mike G

Sure add a getter to the FullDuplexSerial object.

PUB GetBuffer(index)
  return rx_buffer[index]

I have to ask... why??? There is probably a better way to handle your business logic.

Cluso99

Just add this spin routine to the FDX spin code and call it.

PUB rxtwice : rxbyte
'' Check if byte received (never waits)
'' returns -1 if no byte received, $00..$FF if byte
'' does not clear from buffer
  rxbyte--
  if rx_tail <> rx_head
    rxbyte := rx_buffer[rx_tail]

You will notice it is just the routine Rxbyte with the buffer decrement line removed.

If you just want to know if there is a char in the buffer you can use Rxavail.

Phil Pilgrim (PhiPi)

Mike G wrote:

I have to ask... why???

Contextual lookahead. 'Seems legit to me. It can be simpler than unbuffering, then having to stash it temporarily because you weren't quite ready for it.

-Phil

william chan

So for FullDuplexSerial_rr004,

I just change this line
rx_tail := (rx_tail + 1) & bufmsk

to become

rx_tail := rx_tail & bufmsk

for the lookahead method?
Thanks.

william chan

Now I think I get it,

I should remove this line
rx_tail := (rx_tail + 1) & bufmsk
totally for the lookahead method right?

I feel so stupid, thanks Cluso and Mike.

Duane Degn

William,

I'm not sure if it would be useful in your case or not, but I modifed Tim Moore's four port serial driver to watch for an end of message character.

With a 512 byte rx buffer, I just let the message sit in the rx buffer until it's complete and then process the message. It has really simplified a lot of my projects. I don't have to continually move bytes from one buffer to another as I watch for the final byte of the message.

The modified driver is attached to post #9 of this thread.