MPC860 IDMA latency question

Roger Williams roger at
Thu Aug 12 17:04:11 EST 1999

[I apologise for asking this here, but Motorola doesn't seem to host a
PPC mailing list like their other MCU lists.]

I'm having trouble getting the throughput estimated by Motorola for
peripheral -> memory IDMA transfers on the MPC860.  In particular,
they seem to claim 10 MBytes/s for single-address (`fly-by') transfers
(level-sensitive DREQ on a 50 MHz part), but as I only get a new SDACK
every 30 clock cycles, I'm lucky to get 1.25 MWords/s, even with
memory set up for zero wait states.

Any ideas of what am I missing here?  (Unfortunately, I can't try the
special single-buffer mode until I receive some rev C devices...)

Roger Williams                         finger me for my PGP public key
Coelacanth Engineering Inc    consulting & turnkey product development
Middleborough, Massachusetts           wireless * datacomm * DSP * ATE
tel +1 508 947-5585 * fax +1 508 861-0278 *

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