Looks like John beat me to it ;-)

Steve played with expanding the buffer a long time ago while we were playing 
with the M100-on-the-Internet but never got it working 100% reliably, so we 
ended up handling XON/XOFF in the bridge hard/software instead which could 
respond instantly.

  ----- Original Message ----- 
  From: John R. Hogerhuis 
  To: Model 100 Discussion 
  Sent: Monday, October 17, 2016 5:05 PM
  Subject: Re: [M100] mComm 1.5

  On Mon, Oct 17, 2016 at 1:11 PM, Kurt McCullum <kurt.mccul...@att.net> wrote:

    John, Thanks for info. Is that a TELCOM limit? The reason I ask is because 
when running virtual T with TS-DOS, I notice that the buffer can go to 255. Or 
at least the byte which holds the buffer size.

  In my experience I've found that all 8-bit bytes go to 2^8 - 1 = 255

  Just teasing :-) It could but it should never in practice have a value > 64.
  Have you observed a higher value than 64?

  It's not a limitation of TELCOM per se, it's a limitation of the receive 
interrupt handler logic and the size of the circular queue-on-array reserved 
for receiving bytes. The same receive handler is used for TELCOM and BASIC 
access to the serial port.

  See http://www.club100.org/ftp/m100-hiddenpowers-3.pdf
  Page 186

  It shows a receive buffer of 64 bytes. If it went beyond the bounds, 
unmasked, I would expect it to corrupt other data structures.

  The high-water mark for the buffer is 40 (the point at which the receive 
handler sends XOFF), which probably makes more sense in the context of a 64 
byte buffer than a 255 byte buffer :-)

  -- John.

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