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Conference 7.286::fddi

Title:	FDDI - The Next Generation

Moderator:	NETCAD::STEFANI

Created:	Thu Apr 27 1989
Last Modified:	Thu Jun 05 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	2259
Total number of notes:	8590

587.0. "DMA for the DECcontrolleur 700 ?" by MFOIS1::DIGNE (Jean-Marc DIGNE 836-5125 Marseille) Wed May 27 1992 12:10

    A question from a customer:
    
    Does the DECcontroller 700 (TURBOchannel) use DMA to transfert data
    from the memory ?
    
    Jean-Marc ---

T.R	Title	User	Personal Name	Date	Lines
587.1	DEFZA has DMA only for receive	KONING::KONING	Paul Koning, A-13683	`Wed May 27 1992 14:00`	5
	No. DEFZA has DMA for received packets, but not for transmitted packets. paul
587.2	20Mb/s or did I miss something ?	ANNECY::ADAM	Fabrice - EIC Annecy/FRANCE	`Thu Jun 04 1992 12:18`	22
	heuh ! no DMA for sending.. I'm right with the following assumptions ? My application has 400kbytes/s to send. Ultrix will copy data from user space to kernel space. This takes 0.5ms for 4Kbytes. The total is then 50ms (5 % CPU). On a DECsystem 5000-200, it takes no less than 1ms to transfer 4Kbytes onto the turbochannel board (due to lentency). Thus, to copy the 400 Kbytes, I need 100ms (10 % CPU). If I saturate the CPU, the maximum could be 2.5 Mbytes/s. (15% CPU for 400Kbytes. I forget the system,protocol overhead). fab.
587.3		KONING::KONING	Paul Koning, A-13683	`Thu Jun 04 1992 17:06`	5
	I think you can do better than 20 Mb/s but probably not drastically better. Among other things it depends on whether you use UDP or TCP. Also, are you using the full (4352) FDDI packet size? paul
587.4		MIPSBX::thomas	The Code Warrior	`Thu Jun 04 1992 19:57`	2
	I've gotten just over 40Mb/sec using DLI on a DS5000/200. TCP and NSP about half that. UDP without checksums can be 35Mb/sec (all these are at 100% CPU)