Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!POSTGRES.BERKELEY.EDU!dillon
From: dillon@POSTGRES.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga.tech
Subject: Re: State of PD system enhancement (was: Two Amigas)
Message-ID: <8909182019.AA06478@postgres.Berkeley.EDU>
Date: 18 Sep 89 20:19:57 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 40

:>	diskperf NET: to my A1000's RAM: drive yields 25 KBytes/sec
:>	(4096 byte buffers).  Raw network throughput is 28 KBytes/sec.
:Is that the theoretical limit on the parallel port?  I'd expect much
:higher throughput.  The serial port can be driven up to 56Kbps or so,
:right?  If (and I realize I'm making a big assumption here, but ...)
:IF it takes about the same amount of effort to send a BYTE down the
:parallel port as a BIT down the serial port, shouldn't the limit be
:around 56Kb/sec?

	I've been talking to Ron Perry, who wrote the basic software
    for a commercial 16 Amiga server using the parallel port.  With
    hardware, he is getting 100KBytes/sec out of it.

	As far as the serial port goes, no, a bit is not the same
    trouble as a byte on the parallel port.  You write bytes to the
    serial port register not bits so the trouble is the same.

	56Kbps = 5.6KBytes/sec (10 bits/byte 8 bits + start + stop)

	The current 28KBytes/sec throughput I'm getting over the
    parallel port is about 35uS/byte.  Most of the time is spent
    hand-shaking between the computers.  With the Amiga you can't
    count cycles like you could on the old C64's and PETs so you
    have to handshake.

:Hmmm.  2:1.  Less of a difference than I'd thought at first.  I'm
:probably just talking through my hat; ignore me... ;-}

	nearer to 5:1.  Theoretically, the maximum transfer rate over
    the parallel port is ~8 to ~10x the maximum transfer rate over a 
    serial port using line loading limits.

	I've heard people running the serial port at 262KBaud 
    (26KBytes/sec).  The only way this can be done that I can think
    of is (1) The machine must have FAST memory so the video doesn't
    interfere, and (2) Interrupts must be disabled during the transfer. 
    That might be good for a hack file transfer but I can't make those
    assumptions for interactive usage.

					-Matt