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

Comments

• Mike G Posts: 2,702

  2012-01-12 19:50 edited 2012-01-12 19:50

  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 Posts: 18,071

  2012-01-12 23:03 edited 2012-01-12 23:03

  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) Posts: 23,514

  2012-01-13 00:17 edited 2012-01-13 00:17

  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 Posts: 1,326

  2012-01-13 01:02 edited 2012-01-13 01:02

  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 Posts: 1,326

  2012-01-13 01:08 edited 2012-01-13 01:08

  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 Posts: 10,588

  2012-01-13 09:09 edited 2012-01-13 09:09

  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.