Date:	Wed, 13 Nov 1996 16:24:22 GMT
From:	kvhk AT ivs4 DOT barco DOT com (Koen Van Herck)
Message-Id:	<9611131624.AA20092@ivs4.>
To:	djgpp AT delorie DOT com
Subject:	movedata() or farnspokel()
Reply-To:	Koen DOT VanHerck AT barco DOT com

I am making some performance measurements of the PCI bus. I have a
test program which writes/reads 1MB of data to a PCI device, and I
time this with uclock(). Currently I have the following code:

  t_start = uclock();
  _farsetsel(memdesc);
  for(adr=start; adr<start+0x00100000;adr+=4)
  {
    _farnspokel(adr, 0xa55a0ff0); 
  }
  t_stop = uclock();

The results are 60 MB/s for writing and 7.5 MB/s for reading. It seems
that the code is efficient enough, because unrolling the loop doesn't
gain anything. Remark the high number for writing: this is because I
write to consecutive addresses which can be combined to bursts on the
PCI bus.

With movedata(), I only get 35 MB/s and 6.7 MB/s. I have noticed that
movedata() uses a repnz movesl instruction. Why is this worse ? 
According to 18.4 of the FAQ, movedata should be better !

If anyone has or wants more information on this, please mail me.

----
Koen Van Herck
Electronic Design Engineer
E-mail: Koen DOT VanHerck AT barco DOT com

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