18 Aug
2015
18 Aug
'15
6:26 p.m.
On 8/18/2015 11:33 AM, Johnny Billquist wrote:
On 2015-08-18 15:09, Jay Jaeger wrote:
Yes, but from what I could tell from its manual, the RLV11 could ONLY
use BR4 - had no jumpers to do anything else - it was designed in the
days of the LSI bus, the QBus precursor, which only had the one signal.
JRJ
On 8/18/2015 7:46 AM, Paul Koning wrote:
Yes, but this discussion regards an RLV11.
It was possible to use several BR levels on a Qbus as well, but in
practice it was not done.
And I suspect the diagnostics wants to know so that they can set the PSW
correctly on interrupts. Just using the default number should be good
enough in the common case.
Johnny On Aug 17, 2015, at 10:48 PM, Jay Jaeger
<cube1 at charter.net> wrote:
BR level is the bus request level for an Interrupt. BR 4 is typical.
On Unibus machines, more of the BR levels were used. The rule of
thumb was BR4 for slow devices (like terminals and printers), BR5 for
fast devices (disks and tapes), BR6 for real time critical devices
(clock, also DECtape because you had to respond to a ?read block
number? interrupt fast enough to start reading the block before it
passed over the heads). BR7 could in theory be used by devices but I
don?t believe it ever was in practice.
paul