bqt at update.uu.se
Tue Aug 18 11:33:19 CDT 2015
On 2015-08-18 15:09, Jay Jaeger wrote:
> On 8/18/2015 7:46 AM, Paul Koning wrote:
>>> 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.
> 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.
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