From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <38D27077.C11A3B28@embeddededge.com> Date: Fri, 17 Mar 2000 12:50:47 -0500 From: Dan Malek MIME-Version: 1.0 To: Alan Mimms CC: Geir Frode Raanes , Richard Hendricks , linuxppc-embedded@lists.linuxppc.org Subject: Re: What is the catch with IDMA on MPC860? References: <20000317.17233800@alanm.penguinpowered.com> Content-Type: text/plain; charset=us-ascii Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: Alan Mimms wrote: > > Regarding the "where does the manual say that the performance stinks" That's an irrelevant question, as no one literally said "the performance stinks", and no one should. If you take a look at the timing diagrams and the CPM performance worksheets, you will find the IDMA is not terribly efficient. This is a system design choice. You can move data significantly faster using PPC core programmed I/O operations. The other system design considerations surround the use of the CPM. If you choose to use the IDMA, it affects other CPM operations. The IDMA could very well statisfy a particular system design. If the feature wasn't there, people would be complaining for that reason. The 860 is a killer communication processor. When you start using some of these other features, it significantly impacts this capability. In the case if IDMA, control signals used for some communication capabilities are lost, and you have to choose configuration options that further erode the communication processing performance. Just be aware of this. -- Dan ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/