Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!henry.jpl.nasa.gov!elroy.jpl.nasa.gov!gryphon!pnet02!lampi From: lampi@pnet02.gryphon.com (Michael Lampi) Newsgroups: comp.sys.apollo Subject: Re: DMA on DN4000 AT-bus Message-ID: <24249@gryphon.COM> Date: 4 Jan 90 19:40:25 GMT Sender: root@gryphon.COM Organization: People-Net [pnet02], Redondo Beach, CA. Lines: 39 >1. Has anyone done a similar thing before? [rest deleted for brevity] Yes, I have written a couple of DN-x0x0 device drivers that do similar things, including one that had to read up to 10 megabytes of data nonstop coming at a data rate of up to a megabyte per second. This was in order to read tape records that were written in the seismic form; i.e., tape blocks that were megabytes in length; where one can not just 'stop the tape and hold it in position' until the Apollo is ready for more. >2. [...deleted] Is it possible to read in a much larger >amount of data (400k) without losing anything ? Yes, depending on your controller, your driver code, and the amount of RAM in your Apollo. You see, the controller or the thing it is attached to must either have a FIFO memory or be able to be re-instructed to transfer more data within .05 milliseconds to achieve the 20,000 data transfers per second rate. The Apollo interrupt mechanism can generally meet this constraint if you don't have anything else occurring on the node with a higher interrupt priority, such as network or disk access. (That's where a FIFO is handy!) The amount of RAM you have comes into play when you realize that the operating system requires about 1 megabyte (round numbers), your application code and stack requires (typically) 1/2 megabyte, etc. I forget what the general rule of thumb is, but it goes something like this: You can wire all the RAM in your system except for about 2 megabytes, which is allocated to the OS. So, in an 8 meg system, you can wire up to a 6 meg buffer. >7. Do I have to upgrade the OS ? I would strongly recommend you upgrade to 9.7.5; however, this should still work on 9.6.1. Michael Lampi MDL Corporation 213/782-7888 fax 213/782-7927 UUCP: {ames!elroy, }!gryphon!pnet02!lampi INET: lampi@pnet02.gryphon.com "My opinions are that of my corporation!"