stevens@hsi.UUCP (Richard Stevens) (08/20/86)
The UDA50 driver supplied with 4.3 sets the "burst rate" of the driver to 3 (UDABURST - 1, where UDABURST is #defined to 4 at the top of the driver). Not having any documentation at all on the UDA50, I'm not quite sure what the burst rate is, but I'd guess its the number of transfers on the Unibus before the controller gives up the bus to someone else ?? Anyway, the 4.2 uda.c that we were running (from Bob Brown at RIACS, Revision 2.1, dated 84/03/05) in effect set the burst rate to 0 - it never set it explicitly, but the appropriate bits were defaulted to zero. With the burst rate set at 3, we were getting a lot of bus-grant lates from an Emulex TC11 tape controller driving two Kennedy 9300 tape drives (125 ips). Only when we set UDABURST to 1 (setting the burst rate to 0) did the problems subside. If you have any devices like the TC11 (8 bytes of buffer!!) on a busy Unibus, you should probably lower the burst rate in the driver. Richard Stevens Health Systems International, New Haven, CT ihnp4 ! hsi ! stevens
davest@tektronix.UUCP (Dave Stewart) (08/25/86)
It is fairly standard practice in these parts to put a UDA-50 on its own unibus. DEC recommends putting a UDA-50 only with other DEC hardware on a unibus, but we have found that even this can cause problems. An interesting development of this is that the VAX 8650 we have here at Tek has a unibus that is designed to have only a UDA-50 because there are no slots for anything else! (Actually, even this can be bent since we got DEC to squeeze a DR11-B on this bus because of timing problems with another device). This strikes me as humorous: most peripheral manufacturers design their equipment around CPU features. Here poor DEC has to design their CPU around their peripherals! Anyway, I degress. If you have more than one unibus, the good money is on moving everything off of the bus that has the UDA-50. Then you should not need to worry about the burst rate or other device-bus contention problems. My apologies to DEC if I have oversimplified this or overstated it. -- David C. Stewart uucp: tektronix!davest Unix Systems Support Group csnet: davest@TEKTRONIX Tektronix, Inc. phone: (503) 627-5418