4.3 uda.c - warning

[Richard Stevens]

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